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June 1984

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Document:	Rainbow Color Graphics Option Programmers Reference Guide
Order Number:	AA-AE36A-TV
Revision:
Pages:	241
Original Filename:	http://bitsavers.org/pdf/dec/rainbow/AA-AE36A-TV_Rainbow_Color_Graphics_Option_Programmers_Reference_Guide_Jun84.pdf

OCR Text

AA-AE36A-TV

Color/Graphics Option
Programmer's Reference Guide

digital equipment corporation

First Printing, June 1984
© Digital Equipment Corporation 1984. All Rights Reserved.

The information in this document is subject to change without notice and should
not be construed as a commitment by Digital Equipment Corporation. Digital
Equipment Corporation assumes no responsibility for any errors that may
appear in this document.
The software described in this document is furnished under a license and may
only be used or copied in accordance with the terms of such license.
No responsibility is assumed for the use or reliability of software on equipment
that is not supplied by DIGITAL or its affiliated companies.
CP/M and CP/M-86 are registered trademarks of Digital Research Inc.
CP/M-8O is a trademark of Digital Research Inc.
uPD7220 is a registered trademark of NEC Electronics U.S.A. Inc.
8088 is a registered trademark of Intel Corporation.
The following are trademarks of Digital Equipment Corporation:

~D~DDmD'"
DEC
DECmate
DECsystem-10
DECSYSTEM-20
DECUS
DECwriter
DIBOL

MASSBUS
PDP

P/OS
Professional
Rainbow
RSTS
RSX

UNIBUS
VAX
VMS

VT
Work Processor

The postage-prepaid READER'S COMMENTS form on the last page of this
document requests the user's critical evaluation to assist us in preparing future
documentation.

Printed in U.S.A.

Contents

Preface

vii

The Intended Audience vii
Organization of the Manual vii
Suggestions for the Reader viii

PART I -

Operating Principles

Chapter 1. Overview

1-1

Hardware Components 1-1
Resolution Modes 1-3
Operational Modes 1-3

Chapter 2. Monitor Configurations
Monochrome Monitor Only
Color Monitor Only 2-3
Dual Monitors 2-4

2-2

Chapter 3. Graphics Option Logic
General 3-1
Data Logic 3-2
Address Logic 3-2
Display Logic 3-6
GDC Command Logic

2-1

3-1

3-9

iii

Contents

Chapter 4. Graphics Option Components
I/O Ports 4- 1
Indirect Register 4-2
Write Buffer 4-2
Write Mask Registers 4-4
Pattern Generator 4-5
Foreground/Background Register
ALU/PS Register 4-8
Color Map 4-9
Mode Register 4- 15
Scroll Map 4-16

PART II -

4-6

Programming Guidelines

Chapter 5. Initialization and Control
Test for Option Present 5- 1
Test for Motherboard Version 5-2
Initialize the Graphics Option 5-6
Controlling Graphics Output 5-24
Modifying and Loading the Color Map

5-1

5-25

Chapter 6. Bitmap Write Setup (General)
Loading the ALU/PS Register 6-1
Loading the Foreground/Background Register

Chapter 7. Area Write Operations
Display Data from Memory 7-1
Set a Rectangular Area to a Color

Setting Up the Pattern Generator
Display a Pixel 8-4
Display a Vector 8-5
Display a Circle 8-9

7-4

8-1

Chapter 9. Text Write Operations
Write a Byte-Aligned Character 9- 1
Define and Position the Cursor 9-32
Write a Text String 9-38

9-1

6-1

6-2

7-1

Chapter 8. Vector Write Operations

4-1

Contents

Chapter 10. Read Operations

10-1

The Read Process 10-1
Read the Entire Bitmap 10-1
Pixel Write After a Read Operation

10-5

Chapter 1 1. Scroll Operations

1 1-1

Vertical Scrolling 11-1
Horizontal Scrolling 11-4

Chapter 12. Programming Notes

12-1

Shadow Areas 12-1
Bitmap Refresh 12-1
Software Reset 12-2
Setting Up Clock Interrupts 12-2
Operational Requirements 12-3
Set-Up Mode 12-3
Timing Considerations 12-4

PART III -

Reference Material

Chapter 13. Option Registers, Buffers, and Maps
I/O Ports 13- 1
Indirect Register 13-3
Write Buffer 13-4
Write Mask Registers 13-5
Pattern Register 13-6
Pattern Multiplier 13-7
Foreground/Background Register
ALU/PS Register 13-9
Color Map 13-10
Mode Register 13-11
Scroll Map 13-12

13-1

13-8

Chapter 14. GDC Registers and Buffers

14-1

Status Register 14-1
FIFO Buffer 14-2

Chapter 15. GDC Commands

15- 1

Introduction 15-1
Video Control Commands 15-2
Display Control Commands 15-8
Drawing Control Commands 15- 13
Data Read Commands 15-1 8

Contents

PART IV -

Appendixes

Appendix A. Option Specification Summary

A-1

Physical Specifications A- 1
Environmental Specifications A-1
Power Requirements A-2
Standards and Regulations A-2
Part and Kit Numbers A-3

Appendix B. Rainbow Graphics Option Appendix C. Getting Help

Block Diagram

B-1

C-1

Index 1-1
Figures
Figure 1. Monochrome Monitor Only System 2-2
Figure 2. Color Monitor Only System 2-3
Figure 3. Dual Monitor System 2-4
Figure 4. Rows and Columns in Display Memory 3-3
Figure 5. Relationship of Display Memory to Address Logic 3-4
Figure 6. GDC Screen Control Parameters 3-8
Figure 7. Write Buffer as Accessed by the CPU and the GDC 4-3
Figure 8. Write Mask ReGISters 4-4
Figure 9. Pattern Generator 4-5
Figure 10. Foreground/Background ReGISter 4-7
Figure 11. Bitmap/Color Map Interaction (medium resolution) 4-10
Figure 12. Bitmap/Color Map Interaction (high resolution) 4-11
Figure 13. Sample Color Map with Loading Sequence 4-12
Figure 14. Scroll Map Operation 4-16
Figure 15. Rainbow Graphics Option - Block Diagram B-3

Tables
Table 1. Colors and Monochrome Intensities - Displayed/Available
Table 2. Intensity Values vs Video Drive Voltages 4-14
Table 3. Clock Interrupt Parameters 12-2

1-1

Preface

The Intended Audience
The Rainbow Color/Graphics Option Programmer's Reference Guide is written for the experienced
systems programmer who will be programming applications that display graphics on Rainbow video
monitors. It is further assumed that the system programmer has had both graphics and 8088 programming experience.
The information contained in this document is not unique to any operating system; however, it is
specific to the 8088 hardware and 8088-based software.

Organization of the manual
The Rainbow Color/Graphics Option Programmer's Reference Guide is subdivided into four parts
containing fifteen chapters and three appendixes as follows:
• PART I -

OPERATING PRINCIPLES contains the following four chapters:

- Chapter 1 provides an overview of the Graphics Option including information on the hardware, logical interface to the CPU, general functionality, color and monochrome ranges, and
model dependencies.
- Chapter 2 describes the monitor configurations supported by the Graphics Option.

vii

Preface

- Chapter 3 discusses the logic of data generation, bitmap addressing, and the GDC's handling
of the screen display.
- Chapter 4 describes the software components of the Graphics Option such as the control
registers, maps, and buffer areas accessible under program control.
• PART II -

PROGRAMMING GUIDELINES contains the following eight chapters:

- Chapter 5 discusses programming the Graphics Option for initialization and control
operations.
- Chapter 6 discusses programming the Graphics Option for setting up bitmap write
operations.
- Chapter 7 discusses programming the Graphics Option for area write operations.
- Chapter 8 discusses programming the Graphics Option for vector write operations.
- Chapter 9 discusses programming the Graphics Option for text write operations.
- Chapter 10 discusses programming the Graphics Option for read operations.
- Chapter 11 discusses programming the Graphics Option for scroll operations.
- Chapter 12 contains programming notes and timing considerations.
• PART III -

REFERENCE MATERIAL contains the following three chapters:

- Chapter 13 provides descriptions and contents of the Graphics Option's registers, buffers,
masks, and maps.
- Chapter 14 provides descriptions and contents of the GDC's status register and FIFO buffer.
- Chapter 15 provides a description of each supported GDC command arranged in alphabetic
sequence within functional grouping.
• PART IV -

APPENDIXES contain the following three appendixes:

- Appendix A contains the Graphics Option's Specification Summary.
- Appendix B is a fold-out sheet containing a block diagram of the Graphics Option.
- Appendix C lists DIGITAL's International Help Line phone numbers.

Suggestions for the Reader
For more information about the Graphics Display Controller refer to the following:

•

uPD7220 CDC Design Manual-NEC Electronics U.S.A. Inc.

•

uPD7220 CDC Design SPecification-NEC Electronics U.S.A. Inc.

viii

Preface

For a comprehensive tutorial/reference manual on computer graphics, consider Fundamentals of
Interactive Computer Graphics by J. D. Foley and A. Van Dam published by Addison-Wesley Publishing Company, 1982.

Terminology
ALU/pS

Arithmetic Logical Unit and Plane Select (register)

Bitmap

Video display memory

GDC

Graphics. Display Controller

Motherboard

A term used to refer to the main circuit board where the processors and main
memory are located - hardware options, such as the Graphics Option, plug
into and communicate with the motherboard

Nibble

A term commonly used to refer to a half byte (4 bits)

Pixel

Picture element when referring to video display output

Resolution

A measure of the sharpness of a graphics image - usually given as the
number of addressable picture elements for some unit of length (pixels per
inch)

RGB

Red, green, blue monitor displays

RGO

Rainbow Graphics Option

RMW

Read/Modify/Write, the action taken when accessing the bitmap during a write
or read cycle

VSS

Video Subsystem

the acronym for the primary additive colors used in color

)

Contents

PART I
Chapter 1. Overview

1-1

Hardware Components 1-1
Video Memory (Bitmap) 1-2
Additional Hardware 1-2
Resolution Modes 1-3
Medium Resolution Mode 1-3
High Resolution Mode 1-3
Operational Modes 1-3

Chapter 2. Monitor Configurations
Monochrome Monitor Only
Color Monitor Only 2-3
Dual Monitors 2-4

2-2

Chapter 3. Graphics Option Logic
General 3-1
Data Logic 3-2
Address Logic 3-2
Display Logic 3-6
Bitmap Logic 3-6
Screen Logic 3-7
GDC Command Logic

\
/

3-9

2-1

3-1

Contents

Chapter 4. Graphics Option Components
I/O Ports 4-1
Indirect Register 4-2
Write Buffer 4-2
Write Mask Registers 4-4
Pattern Generator 4-5
Foreground/Background Register
ALU/PS Register 4-8
Color Map 4-9
Loading the Color Map 4-12
Video Drive Voltages 4-13
Mode Register 4- 15
Scroll Map 4-16
Loading the Scroll Map 4-17

4-6

4-1

1
Overview
Hardware Components
The Graphics Option is a user-installable module that adds graphics and color display capabilities to
the Rainbow system. The graphics module is based on a NEC uPD7220 Graphics Display Controller
(GDC) and an 8 X 64K dynamic RAM video memory that is also referred to as the bitmap.
The Graphics Option is supported, with minor differences, on Rainbow systems with either the model
A or model B motherboard. The differences involve the number of colors and monochrome intensities that can be simultaneously displayed and the number of colors and monochrome intensities that
are available to be displayed (see Table 1). Chapter 5 includes a programming example of how you
can determine which model of the motherboard is present in your system.
Table 1. Colors and Monochrome Intensities -

Displayed/Available

MED. RESOLUTION

HIGH RESOLUTION

CONFIG.

MODEL

COLOR

MONO.

COLOR

MONO.

MONOCHROME
MONITOR
ONLY

100-A

N/A

4/4

N/A

4/4

100-8

N/A

16/16

N/A

4/16

100-A

16/1024

N/A

4/1024

N/A

100-8

16/4096

N/A

4/4096

N/A

100-A

16/4096

4/4

4/4096

4/4

100-8

16/4096

16/16

4/4096

4/16

COLOR
MONITOR
ONLY

DUAL
MONITORS

LJ-0212

1-1

Overview

The GDC, in addition to performing the housekeeping chores for the video display, can also:
•

Draw lines at any angle

•

Draw arcs of specified radii and length

• Fill rectangular areas
• Transfer character bit-patterns from font tables in main memory to the bitmap

Video Memory (Bitmap)
The CPUs on the motherboard have no direct access to the bitmap memory. All writes are performed by the external graphics option hardware to bitmap addresses generated by the GDC.
The bitmap is composed of eight 64K dynamic RAMs. This gives the bitmap a total of 8 X 64K of
display memory. In high resolution mode, this memory is configured as two planes, each 8 X 32K.
In medium resolution mode, this memory is configured as four planes, each 8 X 16K. However, as
far as the GDC is concerned, there is only one plane. All plane interaction is transparent to the GDC.
Although the bitmap is made up of 8 X 64K bits, the GDC sees only 16K of word addresses in high
resolution mode (2 planes X 16 bits X 16K words). Similarly, the GDC sees only 8K of word
addresses in medium resolution mode (4 planes X 16 bits X 8K words). Bitmap address zero is
displayed at the upper left corner of the monitor screen.

Additional Hardware
The option module also contains additional hardware that enhances the performance and versatility of
the GDC. This additional hardware includes:
• A 16 X 8-bit Write Buffer used to store byte-aligned or word-aligned characters for high
performance text writing or for fast block data moves from main memory to the bitmap
• An 8-bit Pattern Register and a 4-bit Pattern Multiplier for improved vector writing
performance
• Address offset hardware (256 X 8-bit Scroll Map) for full and split-screen vertical scrolling
• ALU/pS register to handle bitplane selection and the write functions of Replace, Complement,
and Overlay
• A 16 X 16-bit Color Map to provide easy manipulation of pixel color and monochrome
intensities
• Readback hardware for reading a selected bitmap memory plane into main memory

1-2

Overview

Resolution Modes
The Graphics Option operates in either of two resolution modes:
• Medium Resolution Mode
• High Resolution Mode

Medium Resolution Mode
Medium resolution mode displays 384 pixels horizontally by 240 pixels vertically by four bitmap
memory planes deep. This resolution mode allows up to 16 colors to be simultaneously displayed on a
color monitor. Up to sixteen monochrome shades can be displayed simultaneously on a monochrome
monitor.

High Resolution Mode
High resolution mode displays 800 pixels horizontally by 240 pixels vertically by two bitmap memory
planes deep. This mode allows up to four colors to be simultaneously displayed on a color monitor.
Up to four monochrome shades can be simultaneously displayed on a monochrome monitor.

Operational Modes
The Graphics Option supports the following modes of operations:
•

WORD MODE to write 16-bit words to selected planes of the bitmap memory for character and
image generation

•

VECTOR MODE to write pixel data to bitmap addresses provided by the GDC

• SCROLL MODE for full- and split-screen vertical scrolling and full-screen horizontal scrolling
•

READBACK MODE to read 16-bit words from a selected plane of bitmap memory for special
applications, hardcopy generation or diagnostic purposes

1-3

2
Monitor Configurations

In the Rainbow system with the Graphics Option installed, there are three possible monitor configurations: Monochrome only, Color only, and Dual (color and monochrome). In all three configurations,
the selection of the option's monochrome output or the motherboard VTI02 video output is controlled by bit two of the system maintenance port (port OAh). A 0 in bit 2 selects the motherboard
VTI02 video output while a 1 in bit 2 selects the option's monochrome output.

2-1

Monitor Configurations

Monochrome Monitor Only
As shown in Figure 1, the monochrome monitor can display either graphics option data or
motherboard data depending on the setting of bit 2 of port OAh. Writing an 87h to port OAh selects
the Graphics Option data. Writing an 83h to port OAh selects the motherboard VT102 data. The red,
green and blue data areas in the Color Map should be loaded with all F's to reduce any unnecessary
radio frequency emissions.
BLUE INTENSITIES
RED INTENSITIES
GREEN INTENSITIES
MONOCHROME INTENSITIES-----4"
~---... MONOCHROME MONITOR

MOTHERBOARD D A T A - - - - -......

PORT OAh (BIT 2)-------~
LJ-0215

Figure 1. Monochrome Monitor Only System

(

2-2

Monitor Configurations

Color Monitor Only
When the system is configured with only a color monitor, as in Figure 2, the green gun does double
duty. It either displays the green component of the graphics output or it displays the monochrome
output of the motherboard VT102 video subsystem. Because the green gun takes monochrome
intensities, all green intensities must be programmed into the monochrome data area of the Color
Map. The green data area of the Color Map should be loaded with all F's to reduce any unnecessary
radio frequency emissions.
BLUE INTENSITIES

----------------------~~BLUEGUN

RED I NTENSITI ES ------------------------...
~ RED GU N
GREEN INTENSITIES
MONOCHROME INTENSITIES
(GREEN DATA)

) - - - - . GREEN GUN
MOTHERBOARD DATA----------1~

PORT OAh (BIT 2)
LJ-0216

Figure 2. Color Monitor Only System

When motherboard VT102 data is being sent to the green gun, the red and blue output must be
turned off at the Graphics Option itself. If not, the red and blue guns will continue to receive data
from the option and this output will overlay the motherboard VT102 data and will also be out of
synchronization. Bit 7 of the Mode Register is the graphics option output enable bit. If this bit is a 1
red and blue outputs are enabled. If this bit is a 0 red and blue outputs are disabled.
As in the monochrome only configuration, bit 2 of port OAh controls the selection of either the
graphics option data or the motherboard VT102 data. Writing an 87h to port OAh enables the option
data. Writing an 83h to port OAh selects the motherboard VT102 data.

2-3

Monitor Configurations

Dual Monitors
In the configuration shown in Figure 3, both a color monitor and a monochrome monitor are available
to the system. Motherboard VTI02 video data can be displayed on the monochrome system while
color graphics are being displayed on the color monitor. If the need should arise to display graphics
on the monochrome monitor, the monochrome intensity output can be directed to the monochrome
monitor by writing an 87h to port OAh. Writing an 83h to port OAh will restore motherboard
VTI02 video output to the monochrome monitor.
BLUE INTENSITIES - - - - - - - - - - - -•• BLUE GUN
RED INTENSITIES - - - - - - - - - - - - - . . RED GUN
GREEN INTENSITIES-------------.. GREEN GUN
MONOCHROME INTENSITIES --~.~
>---~ MONOCHROME MONITOR

MOTHERBOARD DATA----~.~

PORT OAh (BIT 2 ) - - - - - - - - - J
LJ-0217

Figure 3. Dual Monitor System

When displaying graphics on the monochrome monitor, the only difference other than the the lack of
color is the range of intensities that can be simultaneously displayed on systems with model A
motherboards.
Systems with model A motherboards can display only four monochrome intensities at anyone time.
Even though sixteen entries can be selected when operating in medium resolution mode, only the
two low-order bits of the monochrome output are active. This limits the display to only four unique
intensities at most. On systems with the model B motherboard, all sixteen monochrome intensities
can be displayed.

2-4

3
Graphics Option logic

General
The Graphics Display Controller (GDC) can operate either on one bit at a time or on an entire 16-bit
word at a time. It is, however, limited to one address space and therefore can only write into one
plane at a time. The Graphics Option is designed in such a manner that while the GDC is doing
single pixel operations on just one video plane, the external hardware can be doing 16-bit word
operations on up to four planes of video memory.
Write operations are multi-dimensioned. They have width, depth, length and time.
• Width refers to the number of pixels involved in the write operation.
•

Depth refers to the number of planes involved in the write operation.

• Length refers to the number of read/modify/write cycles the GDC is programmed to perform.
• Time refers to when the write operation occurs in relation to the normal housekeeping operations the GDC has to perform in order to keep the monitor image stable and coherent.

3-1

Graphics Option Logic

Data Logic
The Graphics Option can write in two modes: word mode (16 bits at a time) and vector mode (one
pixel at a time).
In word mode, the data patterns to be written into the bitmap are based on bit patterns loaded into
the Write Buffer, Write Mask, and the Foreground/Background Register, along with the type of
write operation programmed into the ALU/PS Register.
In vector mode, the data patterns to be written to the bitmap are based on bit patterns loaded into
the Pattern Register, the Pattern Multiplier, the Foreground/Background Register, and the type of
write operation programmed into the ALU/PS Register.
In either case, the data will be stored in the bitmap at a location determined by the addressing logic.

Address Logic
The addressing logic of the Graphics Option is responsible for coming up with the plane, the line
within the plane, the word within the line, and even the pixel within the word under some conditions.
The display memory on the Graphics Option is one-dimensional. The GDC scans this linear memory
to generate the two dimensional display on the CRT. The video display is organized similarly to the
fourth quadrant of the Cartesian plane with the origin in the upper left corner. Row addresses (y
coordinates of pixels) start at zero and increase downwards while column addresses (x coordinates of
pixels) start at zero and increase to the right (see Figure 4). Pixel data is stored in display memory
by column within row.

3-2

Graphics Option Logic

COLUMN (X)

ROW(Y!

(0,0)

(1,0)

(2,0)

(N,O)

(0,1)

(1,1)

(2,1)

(N,1 )

(0,2)

(1,2)

(2,2)

(N,2)

(O,M)

(1,M)

(2,M)

(N,M)

• • •

•
•
•
M

LJ-0218

Figure 4. Rows and Columns in Display Memory

The GDC accesses the display memory as a number of 16-bit words where each bit represents a
pixel. The number of words defined as well as the number of words displayed on each line is
dependent on the resolution. The relationship between words and display lines is shown in Figure 5.

3-3

Graphics Option Logic

""----------- WORDS/LINE DEFINED ---------~~I

I...t-------

WORDS/LINE DISPLAYED ------I~~I

LINE 0

Q-l

P-l

LINE 1

P+l

P+2

P+Q-l

2P-l

LINE 2

2P+l

2P+Q-l

3P-l

•

3P+Q-l

4P-l

•

4P+Q-l

5P-l

l,/

l,.;

•

LINE N-l

(M-l )P

MP-l

1N-1 I

NP-l

WHERE:

= WORDS/LINE DEFINED

- 32 IN MEDIUM RESOLUTION.
- 64 IN HIGH RESOLUTION.

= WORDS/LINE DISPLAYED

- 24 IN MEDIUM RESOLUTION
- 50 IN HIGH RESOLUTION

= NO. OF LINES DEFINED

- 256

= NO. OF LINES DISPLAYED

- 240
LJ-0219

Figure 5. Relationship of Display Memory to Address Logic

3-4

Graphics Option Logic

In order to address specific pixels, the GDC requires the word address and the pixel location within
that word. The conversion of pixel coordinates to addresses in display memory is accomplished by
the following formulas:
Given the pixel coordinates (x,y):
Word Address of pixel = (words/line defined * y) + integer(x/16)
Pixel Address within word
= remainder(x/16) * 16

Because the Graphics Option is a multi-plane device, a way is provided to selectively enable and
disable the reading and writing of the individual planes. This function is performed by the ALUjPS
and Mode registers. More than one plane at a time can be enabled for a write operation; however,
only one plane can be enabled for a read operation at anyone time.
The entire address generated by the GDC does not go directly to the bitmap. The low-order six bits
address a word within a line in the bitmap and do go directly to the bitmap. The high-order eight bits
address the line within the plane and these bits are used as address inputs to a Scroll Map. The
Scroll Map acts as a translator such that the bitmap location can be selectively shifted in units of 64
words. In high resolution mode, 64 words equate to one scan line; in medium resolution mode, they
equate to two scan lines. This allows the displayed vertical location of an image to be moved in 64word increments without actually rewriting it to the bitmap. Programs using this feature can provide
full and split screen vertical scrolling. The Scroll Map is used in all bitmap access operations: writing,
reading, and refreshing.
If an application requires addressing individual pixels within a word, the two 8-bit Write Mask
Registers can be used to provide a 16-bit mask that will write-enable selected pixels. Alternately, a
single pixel vector write operation can be used.

There is a difference between the number of words/line defined and the number of words/line
displayed. In medium resolution, each scan line is 32 words long but only 24 words are displayed (24
words * 16 bits/word = 384 pixels). The eight words not displayed are unusable. Defining the length
of the scan line as 24 words would be a more efficient use of memory but it would take longer to
refresh the memory. Because display memory is organized as a 256 by 256 array, it takes 256 bytes
of scan to refresh the entire 64K byte memory. Defining the scan line length as 32 words long
enables the entire memory to be refreshed in four line scan periods. Defining the scan line length as
24 words long would require five line scans plus 16 bytes.
Similarly, in high resolution, each scan line is 64 words long but only 50 words are displayed. With a
64 word scan line length, it takes two line scan periods to refresh the entire 64K byte memory. If
the scan line length were 50 words, it would take two lines plus 56 bytes to refresh the memory.
Another advantage to defining scan line length as 32 or 64 words is that cursor locating can be
accomplished by a series of shift instructions which are considerably faster than multiplying.

3-5

Graphics Option Logic

Display logic
The display logic of the Graphics Option will be discussed as it applies to both the bitmap and the
screen.

Bitmap Logic
Data in the bitmap does not go directly to the monitor. Instead, the bitmap data is used as an
address into a Color Map. The output of this Color Map, which has been preloaded with color and
monochrome intensity values, is the data that is sent to the monitor.
In medium resolution mode there are four planes to the bitmap; each plane providing an address bit
to the Color Map. Four bits can address sixteen unique locations at most. This gives a maximum of
16 addressable Color Map entries. Each Color Map entry is 16 bits wide. Four of the bits are used
to drive the color monitor's red gun, four go to the green gun, four go to the blue gun, and four
drive the output to the monochrome monitor. In systems with the Model 100-A motherboard, only
the two low-order bits of the monochrome output are used. Therefore, although there are 16 possible monochrome selections in the Color Map, the number of unique intensities that can be sent to
the monochrome monitor is four.
In high resolution mode there are two planes to the bitmap; each plane providing an address bit to
the Color Map. Two bits can address four entries in the Color Map at most. Again, each Color Map
entry is sixteen bits wide with 12 bits of information used for color and four used for monochrome
shades. In systems with the Model 100-A motherboard, only the two low-order bits of the monochrome output are used. This limits the number of unique monochrome intensities to four.
Although the Color Map is 16 bits wide, the color intensity values are loaded one byte at a time.
First, the 16 pairs of values representing the red and green intensities are loaded into bits 0 through
7 of the map. Then, the 16 pairs of values representing the blue and monochrome intensities are
loaded into bits 8 through 15 of the map.

3-6

Graphics Option Logic

Screen Logic
The image displayed on the screen is generated by an electron beam performing a series of horizontal line scans from left to right. At the end of each horizontal scan line, a horizontal retrace takes
place at which time the electron beam reverses its horizontal direction. During this horizontal
retrace, the electron beam is also being moved down to the beginning of the next scan line. When
the last line has completed its horizontal retrace, a vertical retrace takes place at which time the
electron beam's vertical movement is reversed and the beam is positioned at the beginning of the
first scan line.
The CDC writes to the bitmap only during the screen's horizontal and vertical retrace periods.
During active screen time, the CDC is taking information out of the bitmap and presenting it to the
video screen hardware. For example, if the CDC is drawing a vector to the bitmap, it will stop
writing during active screen time and resume writing the vector at the next horizontal or vertical
retrace.

In addition to the active screen time and the horizontal and vertical retrace times, there are several
other screen control parameters that precede and follow the active horizontal scans and active lines.
These are the Vertical Front and Back Porches and the Horizontal Front and Back Porches. The
relationship between the screen control parameters is shown in Figure 6. Taking all the parameters
into account, the proportion of active screen time to bitmap writing time is approximately four to
one.

3-7

Graphics Option Logic

GDC VIDEO CONTROL PARAMETERS

VERTICAL {
FRONT
PORCH

~O~---

(3 LINES)

~~O----------------~---

-------------~---~
o DOD
------

~OO---------- - - - - - - - - -<l- - - - - (J"'OO----------

~~-a------~~----------------~----------------------0 -0
- -0- 0- -

------------~------

o 0 0 0
-----------------~----~o-o-----------------------_+--------------------
-----

ACTIVE
DISPLAY

O"Lj-o __ - - - - - - - - - - - - - - -<)-- - - -

(240 LINES)

0 0 .p

----------

____ -4--

0"z:>-6- - - - - - - - ___ -4--

______ ----<r"----~ClO-----~~--------------+_------------------___ ----E2-0-~

-- ---- --- ------~ - --O"O-a -- ----- ----------:----(j~-O---- - - - - - - - - ____ <1---VERTICAL
BACK
PORCH

O"cns------ - - - - -<l- - -

(16 LINES)

---- - -----~--- -------

0 0 0
-o
---

________ ~!l.Q.>J
0" ~ -0 ---:,.....::'----------------+--------------------

________ ---<l-----

HIGH
RESOLUTION

MEDIUM
RESOLUTION

o 0 0

HORIZONTAL FRONT PORCH (WORDS)

o 0 0

HORIZONTAL BACK PORCH (WORDS)

-<l- --

HORIZONTAL RETRACE (WORDS)

HORIZONTAL ACTIVE (WORDS)

HORIZONTAL INACTIVE (VERTICAL FRONT & BACK PORCHES)
VERTICAL RETRACE (LINES)

3
LJ·0220

Figure 6. GDC Screen Control Parameters

3-8

Graphics Option Logic

GDC Command logic
Commands are passed to the GDC command processor from the Rainbow system by writing command bytes to port 57h and parameter bytes to port 56h. Data written to these two ports is stored
in the GDC's FIFO buffer, a 16 x 9-bit area that is used to both read from and write to the GDC.
The FIFO buffer operates in half-duplex mode - passing data in both directions, one direction at a
time. The direction of data flow at anyone time is controlled by GDC commands.
When commands are stored in the FIFO buffer, a flag bit is associated with each data byte depending
on whether the data byte was written to the command address (57h) or the parameter address (56h).
A flag bit of 1 denotes a command byte; a flag bit of 0 denotes a parameter byte. The command
processor tests this flag bit as it interprets the contents of the FIFO buffer.
The receipt of a command byte by the command processor signifies the end of the previous command and any associated parameters. If the command is one that requires a response from the GDC
such as RDAT, the FIFO buffer is automatically placed into read mode and the buffer direction is
reversed. The specified data from the bitmap is loaded into the FIFO buffer and can be accessed by
the system using read operations to port 57h. Any commands or parameters in the FIFO buffer that
follow the read command are lost when the FIFO buffer's direction is reversed.
When the FIFO buffer is in read mode, any command byte written to port 57h will immediately
terminate the read operation and reverse the buffer direction to write mode. Any data that has not
been read by the Rainbow system from the FIFO buffer will be lost.

3-9

(

4
Graphics Option Components

I/O Ports
The CPUs on the Rainbow system's motherboard use a number of 8-bit I/O ports to exchange
information with the various subsystems and options. The I/O ports assigned to the Graphics Option
are ports 50h through 57h. They are used to generate and display graphic images, inquire status,
and read the contents of video memory (bitmap). The function of each of the Graphics Option's I/O
ports is as follows:
Port

Function

50h

Graphics option software reset. Any write to this port also resynchronizes the
read/modify/write memory cycles of the Graphics Option to those of the GDC.

5Ih

Data written to this port is loaded into the area selected by the previous write to port 53h.

52h

Data written to this port is loaded into the Write Buffer.

53h

Data written to this port provides address selection for indirect addressing (see Indirect
Register).

54h

Data written to this port is loaded into the low-order byte of the Write Mask.

55h

Data written to this port is loaded into the high-order byte of the Write Mask.

56h

Data written to this port is loaded into the GDC's FIFO Buffer and flagged as a parameter.
Data read from this port reflects the GDC status.

57h

Data written to this port is loaded into the GDC's FIFO Buffer and flagged as a command.
Data read from this port reflects information extracted from the bitmap.

)
4-1

Graphics Option Components

Indirect Register
The Graphics Option uses indirect addressing to enable it to address more registers and storage
areas on the option module than there are address lines (ports) to accommodate them. Indirect
addressing involves writing to two ports. A write to port 53h loads the Indirect Register with a bit
array in which each bit selects one of eight areas.
The Indirect Register bits and the corresponding areas are as follows:

Bit

Area Selected

Write Buffer (*)

Pattern Multiplier

Pattern Register

Foreground/Background Register

ALU/PS Register

Color Map (*)

Mode Register

Scroll Map (*)

(*)

Also clears the associated index counter

Mter selecting an area by writing to port 53h, you access and load data into most selected areas by
writing to port 51h. For the Write Buffer however, you need both a write of anything to port 51h to
access the buffer and clear the counter and then a write to port 52h to load the data.

Write Buffer
A 16 X 8-bit Write Buffer provides the data for the bitmap when the Graphics Option is in Word
Mode. You can use the buffer to transfer blocks of data from the system's memory to the bitmap.
The data can be full screen images of the bitmap or bit-pattern representations of font characters
that have been stored in motherboard memory. The buffer has an associated index counter that is
cleared when the Write Buffer is selected.
Although the CPU accesses the Write Buffer as sixteen 8-bit bytes, the GDC accesses the buffer as
eight 16-bit words. (See Figure 7.) A 16-bit Write Mask gives the GDC control over individual bits
of a word.

(
4-2

Graphics Option Components

AS THE CPU ACCESSES IT
BYTE

HIGH BYTE

AS THE GDC ACCESSES IT
WORD

LOW BYTE

WORD

0,1

2,3

4,5

6,7

8,9

10,11

12,13

14,15

I------~
I------~

5
6

7
LJ-0221

Figure 7. Write Buffer as Accessed by the CPU and the GDC

The output of the Write Buffer is the inverse of its input. If a word is written into the buffer as
FFB6h, it will be read out of the buffer as 0049h. To have the same data written out to the bitmap
as was received from the CPU requires an added inversion step. You can exclusive or (XOR) the
CPU data with FFh to pre-invert the data before going through the Write Buffer. Alternately, you
can write zeros into the Foreground Register and ones into the Background Register to re-invert the
data after it leaves the Write Buffer and before it is written to the bitmap. Use one method or the
other, not both.
In order to load data into the Write Buffer, you first write an FEh to port 53h and any value to port
51h. This not only selects the Write Buffer but also sets the Write Buffer Index Counter to zero.
The data is then loaded into the buffer by writing it to port 52h in high-byte low-byte order. If more
than 16 bytes are written to the buffer the first 16 bytes will be overwritten.
If you load the buffer with less than 16 bytes (or other than a multiple of 16 bytes for some reason
or other) the GDC will find an index value other than zero in the counter. Starting at a location other
than zero alters the data intended for the bitmap. Therefore, before the GDC is given the command
to write to the bitmap, you must again clear the Write Buffer Index Counter so that the GDC will
start accessing the data at word zero.

4-3

Graphics Option Components

Write Mask Registers
When the Graphics Option is in Word Mode, bitmap operations are carried out in units of 16-bit
words. A 16-bit Write Mask controls the writing of individual bits within a word. A zero in a bit
position of the mask allows writing to the corresponding position of the word. A one in a bit position
of the mask disables writing to the corresponding position of the word.
While the GDC accesses the mask as a 16-bit word, the CPU accesses the mask as two of the
Graphic Option's I/O ports. The high-order Write Mask Register is loaded with a write to port 55h
and corresponds to bits 15 through 8 of the Write Mask. The low-order Write Mask Register is
loaded with a write to port 54h and corresponds to bits 7 through 0 of the Write Mask. (See Figure
8.)
AS ACCESSED BY
THE CPU
PORT 55h

PORT 54h

7-------------------0 7------------------0
WRITE MASK (HIGH)

WRITE MASK (LOW)

15---------------------------------------0
WORD AS ACCESSED BY GDC
LJ-0222

Figure 8. Write Mask Registers

4-4

Graphics Option Components

Pattern Generator
When the Graphics Option is in Vector Mode, the Pattern Generator provides the data to be written
to the bitmap. The Pattern Generator is composed of a Pattern Register and a Pattern Multiplier.
The Pattern Register is an 8-bit recirculating shift register that is first selected by writing FBh to
port 53h and then loaded by writing an 8-bit data pattern to port 5Ih.
The Pattern Multiplier is a 4-bit register that is first selected by writing FDh to port 53h and then
loaded by writing a value of O-Fh to port 5Ih.
NOTE
You must load the Pattern Multiplier before loading the Pattern Register.

Figure 9 shows the logic of the Pattern Generator. Data destined for the bitmap originates from the
low-order bit of the Pattern Register. That same bit continues to be the output until the Pattern
Register is shifted. When the most significant bit of the Pattern Register has completed its output
cycle, the next bit to shift out will be the least significant bit again.
OPTION
CLOCK

3
PATTERN MULTIPLlER----.,...
(LOADED FROM CPU)

MULTIPLIER
SHIFT
CLOCK

---I."

PATTERN REGISTER
(LOADED FROM CPU)

1--

DATA PATTERN

L ___________________ I

SHIFTED BITS RECIRCULATED
DATA BIT OUTPUT
TO WRITE CIRCUITRY
LJ-0223

Figure 9. Pattern Generator

4-5

Graphics Option Components

The shift frequency is the write frequency from the option clock divided by 16 minus the value in
the Pattern Multiplier. For example, if the value in the Pattern Multiplier is 12, the shift frequency
divisor would be 16 minus 12 or four. The shift frequency would be one fourth of the write frequency and therefore each bit in the Pattern Register would be replicated in the output stream four
times. A multiplier of 15 would take 16 - 15 or one write cycle for each Pattern Register bit shifted
out. A multiplier of five would take 16 - 5 or 11 write cycles for each bit in the Pattern Register.

NOTE
Do not change the contents of the Pattern Multiplier or the Pattern Register before the GDC has completed all pending vector mode write operations. If you do, the vector pattern that is in the process of being displayed
will take on the new characteristics of the Pattern Generator.

Foreground/Background Register
The Foreground/Background Register is an eight-bit write-only register. The high-order nibble is the
Foreground Register; the low-order nibble is the Background Register. Each of the four bitmap
planes has a Foreground/Background bit-pair associated with it (see Figure 10). The bit settings in
the Foreground/Background Register, along with the mode specified in the ALU/PS Register, determine the data that is eventually received by the bitmap. For example; if the mode is REPLACE, an
incoming data bit of 0 is replaced by the corresponding bit in the Background Register. If the
incoming data bit is a 1, the bit would be replaced by the corresponding bit in the Foreground
Register.
Each bitmap plane has its own individual Foreground/Background bit pair. Therefore, it is possible
for two enabled planes to use the same incoming data pattern and end up with different bitmap
patterns.

4-6

Graphics Option Components

FOREGROUND
REGISTER

BACKGROUND
REGISTER

01
2

PLANE 0
PLANE 1
PLANE 2
PLANE 3

LJ-0224

Figure 10. Foreground/Background Register

NOTE
Do not change the contents of the Foreground/Background Register before
the GDC has completed all pending write operations. If you do, the information that is in the process of being displayed will take on the new values of
the Foreground/Background Register.

4-7

Graphics Option Components

ALU IPS Register
The ALUjPS Register has two functions.

Bits through 3 of the ALUjPS Register are used to inhibit writes to one or more of the bitmap
planes. If you could not inhibit writes to the bitmap planes, each write operation would affect all
available planes. When a plane select bit is set to 1, writes to that plane will be inhibited. When a
plane select bit is set to 0, writes to that plane will be allowed.

NOTE
During a readback mode operation, all plane select bits should be set to
ones to prevent accidental changes to the bitmap data.
Bits 4 and 5 of the ALU/PS Register define an arithmetic logic unit function. The three logic
functions supported by the option are REPLACE, COMPLEMENT, and OVERLAY. These functions
operate on the incoming data from the Write Buffer or the Pattern Generator as modified by the
Foreground/Background Register as well as the current data in the bitmap and generate the new
data to be placed into the bitmap.
When the logic unit is operating in REPLACE mode, the current data in the bitmap is replaced by
the Foreground/Background data selected as follows:

• An incoming data bit

°selects the Background data.

• An incoming data bit 1 selects the Foreground data.
When the logic unit is operating in COMPLEMENT mode, the current data in the bitmap is modified
as follows:
• An incoming data bit

°results in no change.

• An incoming data bit 1 results in the current data being exclusively or'ed (XOR) with the
appropriate Foreground bit. If the Foreground bit is 0, the current data is unchanged. If the
Foreground bit is 1, the current data is complemented by binary inversion. In effect, the
Foreground Register acts as a plane select register for the complement operation.

4-8

Graphics Option Components

When the logic unit is operating in OVERLAY mode, the current data in the bitmap is modified as
follows:
• An incoming data bit 0 results in no change.
• An incoming data bit 1 results in the current data being replaced by the appropriate Foreground
bit.

NOTE
Do not change the contents of the ALU IPS Register before the GDC has
completed all pending write operations. If you do, the information that is in
the process of being displayed will take on the new characteristics of the
ALU/PS Register.

Color Map
The Color Map is a 16 X 16-bit RAM area where each of the 16 entries is composed of four 4-bit
values representing color intensities. These values represent, from high order to low order, the
monochrome, blue, red, and green outputs to the video monitor. Intensity values are specified in
inverse logic. At one extreme, a value of zero represents maximum intensity (100% output) for a
particular color or monochrome shade. At the other extreme, a value of OFh represents minimum
intensity (zero output).
Bitmap data is not directly displayed on the monitor, each bitmap plane contributes one bit to an
index into the Color Map. The output of the Color Map is the data that is passed to the monitor.
Four bitmap planes (medium resolution) provide four bits to form an index allowing up to 16 intensities of color or monochrome to be simultaneously displayed on the monitor. Two bitmap planes (high
resolution) provide two bits to form an index allowing only four intensities of color or monochrome to
be simultaneously displayed on the monitor.

4-9

Graphics Option Components

In Figure 11, a medium resolution configuration, the bitmap data for the display point x,y is 0110b.
This value, when applied as an index into the Color Map, selects the seventh entry out of a possible
sixteen. Each Color Map entry is sixteen bits wide. Four of the bits are used to drive the color
monitor's red gun, four go to the green gun, four go to the blue gun, and four drive the output to
the monochrome monitor. The twelve bits going to the color monitor support a color palette of 4096
colors; the four bits to the monochrome monitor support 16 shades. (In systems with the Model 100A motherboard, only the two low-order bits of the monochrome output are active. This limits the
monochrome output to four unique intensities.)
BITMAP

COLOR MAP

/
/

PLANE 0
/

•
•
•

BITMAP DATA

PLANE 1

0110b

•6

•
•
•
•

PLANE 2

PLANE 3

•

X,Y
4(*) BITS OF MONOCHROME LEVEL TO MONO. MONITOR
4 BITS OF BLUE LEVEL TO COLOR MONITOR
4 BITS OF RED LEVEL TO COLOR MONITOR

4 BITS OF GREEN LEVEL TO COLOR MONITOR
(*) 2 LOW-ORDER BITS ON MODEL 100-A SYSTEMS
LJ-0225

Figure 11. Bitmap/Color Map Interaction (medium resolution)

4-10

Graphics Option Components

In Figure 12, a high resolution configuration, the bitmap data for point (x,y) is lOb. This value, when
applied as an index into the Color Map, selects the third entry out of a possible four. Again, each
Color Map entry is sixteen bits wide; 12 bits of information are used for color and four are used for
monochrome. (In systems with the Model 100-A motherboard, only the two low-order bits of the
monochrome output are active. This limits the monochrome output to four unique intensities.)
BITMAP
PLANE

COLOR MAP

/
/

BITMAP DATA

a
1

I
I

PLANE 1

,1
I
I
I

(X,Y)

•
•
•
15

4(*) BITS OF MONOCHROME LEVEL TO MONO. MONITOR
4 BITS OF BLUE LEVEL TO COLOR MONITOR
4 BITS OF RED LEVEL TO COLOR MONITOR
4 BITS OF GREEN LEVEL TO COLOR MONITOR

(*) 2 LOW-ORDER BITS ON MODEL 100-A SYSTEMS
LJ-0226

Figure 12. Bitmap/Color Map Interaction (high resolution)

4-11

Graphics Option Components

Loading the Color Map
The Graphics Option accesses the Color Map as sixteen 16-bit words. However, the CPU accesses
the Color Map as 32 eight-bit bytes. The 32 bytes of intensity values are loaded into the Color Map
one entire column of 16 bytes at a time. The red and green values are always loaded first, then the
monochrome and blue values. (See Figure 13.)

2ND 16 BYTES
LOADED BY
THE CPU

1ST 16 BYTES
LOADED BY
THE CPU

4 3

ADDRESS
VALUE

MONO.
DATA

BLUE
DATA

RED
DATA

GREEN
DATA

COLOR
DISPLAYED

MONOCHROME
DISPLAYED

BLACK

RED

•

GREEN

BLUE

MAGENTA

CYAN

YELLOW

•

•
•
•

i.-'

•
•

G
R
A
Y
S
H
A
D
E
S

•

•
•
•

WHITE

Figure 13. Sample Color Map With Loading Sequence

4-12

•

LJ-0227

Graphics Option Components

Writing the value DFh to port S3h selects the Color Map and also clears the Color Map Index
Counter to zero. To load data into the Color Map requires writing to port Slh. Each write to port
Slh will cause whatever is on the motherboard data bus to be loaded into the current Color Map
location. After each write, the Color Map Index Counter is incremented by one. If 33 writes are
made to the Color Map, the first Color Map location will be overwritten.

NOTE
Do not change the contents of the Color Map before the GDC has completed all pending write operations. If you do, the information that is in the
process of being displayed will take on the new Color Map characteristics.

Video Drive Voltages
The output of the Color Map, as shown in Figures 11 and 12, consists of four 4-bit values that
represent the red, green, blue, and monochrome intensities to be displayed on some applicable
monitor. These four intensity values are the input to four digital-to-analog converters. (Refer to the
block diagram in Appendix B.) The output of these converters are the video drive voltages that are
applied to pins 9 through 12 of the J3 Video Output Jack.
The output of the digital-to-analog converters for the red, green, and blue intensities is not dependent on the model of the system motherboard. The digital-to-analog converter for the monochrome
intensities, however, produces different output depending on whether the motherboard is a model A
or a model B. On systems with a model A motherboard, only the two low-order bits of the intensity
value are active. This provides a limited range of only four output voltages for the m()nochrome
signal. On a color monitor only configuration, where the green output is derived from the monochrome portion of the Color Map, the same limited range applies. On systems with a model B
motherboard, all four bits of the intensity value are active. This provides the full range of 16 output
voltages for the red, green, blue, and monochrome signals. The conversion of Color Map intensity
values to video drive voltages for each of these ranges are shown in Table 2.
The perceived intensity of a display is not linearly related to the video drive voltages. A given
difference in drive voltage at the high end of the range is not as noticeable as the same difference
occurring at the low end of the range.

4-13

Graphics Option Components

Table 2. Intensity Values vs Video Drive Voltages

INTENSITY VALUES

VIDEO DRIVE VOLTAGES (NORMALIZED)

HEX

BINARY

LIMITED RANGE

FULL RANGE

0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111

1.09
0.79
0.71
0.09
1.09
0.79
0.71
0.09
1.09
0.79
0.71
0.09
1.09
0.79
0.71
0.09

1.00
0.85
0.79
0.73
0.67
0.61
0.55
0.49
0.43
0.38
0.31
0.26
0.21
0.12
0.07
0.00

1
2
3
4
5
6
7
8
9
A
B
C
D
E
F

LIMITED RANGE: MODEL A -

ALL MONOCHROME OUTPUT
GREEN OUTPUT ON COLOR
MONITOR ONLY SYSTEM

FULL RANGE:

RED/BLUE OUTPUT ON COLOR
MONITOR ONLY SYSTEM
RED/GREEN/BLUE OUTPUT ON
DUAL MONITOR SYSTEM
RED/BLUE/GREEN/MONOCHROME
OUTPUT ON ALL SYSTEMS

MODEL A MODEL B -

LJ-0259

4-14

Graphics Option Components

Mode Register
The Mode Register is an 8-bit multi-purpose register that is loaded by first selecting it with a write
of BFh to port 53h and then writing a data byte to port 51h. The bits in the Mode Register have the
following functions:
• Bit 0 determines the resolution mode:

o = medium resolution mode (384 pixels across)
1 = high resolution mode (800 pixels across)
• Bit 1 determines the write mode:
0= word mode, 16 bits/RMW cycle, data from Write Buffer
1 = vector mode, 1 bit/RMW cycle, data from Pattern Generator
• Bits 3 and 2 select a bitmap plane for readback mode operation:
00 = plane 0
01 = plane 1
10 = plane 2
11 = plane 3
• Bit 4 determines the option's mode of operation:

o = read mode, bits 3 and 2 determine readback plane
1 = write mode, writes to the bitmap allowed but not mandatory
• Bit 5 controls writing to the Scroll Map:

o = writing is enabled (after selection by the Indirect Register)
1 = writing is disabled
• Bit 6 controls the interrupts to the CPU generated by the Graphics Option every time the GDC
issues a vertical sync pulse:

o = interrupts are disabled, any pending interrupts are cleared
1 = interrupts are enabled
• Bit 7 controls the video data output from the option:

o = output is disabled, other option operations still take place
1 = output is enabled

NOTE
Do not change the contents of the Mode Register before the GDC has
completed all pending write operations. If you do, the functions controlled
by the Mode Register will take on the new characteristics and the results
may be indeterminate.

4-15

Graphics Option Components

Scroll Map
The Scroll Map is a 256 X 8-bit recirculating ring buffer that is used to offset scan line addresses in
the bitmap in order to provide full and split-screen vertical scrolling. The entire address as generated
by the GDC does not go directly to the bitmap. Only the low-order six bits of the GDC address go
directly to the bitmap. They represent one of the 64 word addresses that are the equivalent of one
scan line in high resolution mode or two scan lines in medium resolution mode. The eight high-order
bits of the GDC address represent a line address and are used as an index into the 256-byte Scroll
Map. The eight bits at the selected location then become the new eight high-order bits of the
address that the bitmap sees. (See Figure 14.) By manipulating the contents of the Scroll Map, you
can perform quick dynamic relocations of the bitmap data in 64-word blocks.
WORD ADDRESS

GDC ADDRESS
BITS 0-5
(WORD)

•

a
GDC ADDRESS
BITS 6-13
(LINE)

-----255

•
•

•
•
•
•
•
•

XXXXXXXX

•

•
•
•

~ • • • • WORD • • • • • • •

OFFSET
SCAN
LINE

SCROLL MAP

BITMAP
LJ-0228

Figure 14. Scroll Map Operation

4-16

Graphics Option Components

Loading the Scroll Map
Start loading the offset addresses into the Scroll Map at the beginning of a vertical retrace. First set
bit 5 of the Mode Register to zero to enable the Scroll Map for writing. Write a 7Fh to port 53h to
select the Scroll Map and clear the Scroll Map Index Counter to zero. Then do a series of writes to
port 5Ih with the offset values to be stored in the Scroll Map. Loading always begins at location zero
of the Scroll Map. With each write, the Scroll Map Index Counter is automatically incremented until
the write operations terminate. If there are more than 256 writes, the index counter loops back to
Scroll Map location zero. This also means that if line 255 requires a change, lines 0-254 will have to
be rewritten first.
All 256 scroll map entries should be defined even if all 256 addresses are not displayed. This is to
avoid mapping undesirable data onto the screen. After the last write operation, bit 5 of the Mode
Register should be set to one to disable further writing to the Scroll Map.
The time spent to load the Scroll Map should be kept as short as possible. During loading, the GDC's
address lines no longer have a path to the bitmap and therefore memory refresh is not taking place.
Delaying memory refresh can result in lost data.
While it is possible to read out of the Scroll Map, time constraints preclude doing both a read and a
rewrite during the same vertical retrace period. If necessary, a shadow image of the Scroll Map can
be kept in some area in memory. The shadow image can be updated at any time and then transferred into the Scroll Map during a vertical retrace.

4-17

Contents

PART 1/
Chapter 5. Initialization and Control

5-1

Test for Option Present 5-1
Example of Option Test 5-1
Test for Motherboard Version 5-2
Example of Version Test for CP/M System 5-2
Example of Version Test for MS-DOS System 5-3
Example of Version Test for Concurrent CP/M System 5-5
Initialize the Graphics Option 5-6
Reset the GDC 5-6
Initialize the GDC 5-7
Initialize the Graphics Option 5-8
Example of Initializing the Graphics Option 5-9
Controlling Graphics Output 5-24
Example of Enabling a Single Monitor 5-24
Example of Disabling a Single Monitor 5-25
Modifying and Loading the Color Map 5-25
Example of Modifying and Loading Color Data in a Shadow Map

Chapter 6. Bitmap Write Setup (General)

6-1

Loading the ALU/PS Register 6-1
Example of Loading the ALU/PS Register 6-1
Loading the Foreground/Background Register 6-2
Example of Loading the Foreground/Background Register

)

6-2

5-26

Contents

Chapter 7. Area Write Operations

7-1

Display Data from Memory 7-1
Example of Displaying Data from Memory 7-1
Set a Rectangular Area to a Color 7-4
Example of Setting a Rectangular Area to a Color

Chapter 8. Vector Write Operations

7-4

8-1

Setting Up the Pattern Generator 8- 1
Example of Loading the Pattern Register 8-1
Example of Loading the Pattern Multiplier 8-3
Display a Pixel 8-4
Example of Displaying a Single Pixel 8-4
Display a Vector 8-5
Example of Displaying a Vector 8-6
Display a Circle 8-9
Example of Drawing a Circle 8-9

Chapter 9. Text Write Operations

9-1

Write a Byte-Aligned Character 9-1
Example of Writing a Byte-Aligned Character 9-1
Define and Position the Cursor 9-32
Example of Defining and Positioning the Cursor 9-32
Write a Text String 9-38
Example of Writing a Text String 9-38

Chapter 10. Read Operations

10- 1

The Read Process 10-1
Read the Entire Bitmap 10-1
Example of Reading the Entire Bitmap 10-2
Pixel Write After a Read Operation 10-5

Chapter 11. Scroll Operations

1 1-1

Vertical Scrolling 11-1
Example of Vertical Scrolling One Scan Line 11-2
Horizontal Scrolling 11-4
Example of Horizontal Scrolling One Word 11-4

Chapter 12. Programming Notes
Shadow Areas 12-1
Bitmap Refresh 12-1
Software Reset 12-2
Setting Up Clock Interrupts 12-2
Operational Requirements 12-3
Set-Up Mode 12-3
Timing Considerations 12-4

12-1

5
Initialization and Control

The examples in this chapter cover the initialization of the Graphics Display Controller (GDC) and
the Graphics Option, the control of the graphics output, and the management of the option's color
palette.

Test for Option Present
Before starting any application, you should ensure that the Graphics Option has been installed on the
Rainbow system. Attempting to use the Graphics Option when it is not installed can result in a
system reset that can in turn result in the loss of application data. The following code will test for
the option's presence.

Example of Option Test
,.********************************************************************
p r

e d

r e

p t i

n - p r e 5 e n t - t e 5 t

te5t if Graphic5 Option i5 pre5ent.
none.
dl = 1
option pre5ent.
dl = 0
option not pre5ent.
regi5ter u5age: ax,dx

purpo5e:
entry:
exit:

*
*
*
*
*
*
*
*

.********************************************************************
,

5-1

Initialization and Control

cseg

segment byte
public
'codesg'
public option_present_test
assume cs:cseg,ds:nothing,es:nothing,ss:nothing
option_present_test
proc
near
mov
dl,1
;set dl for option present
in
al,8
;input from port 8
test
al,04h
;test bit 2 to see if option present
j z
opt1
;if option is present, exit
xor
dl,dl
;else, set dl for option not present
ret
opt1:
option_present_test
endp
cseg
ends
end

Test for Motherboard Version
When you initially load or subsequently modify the Color Map, it is necessary to know what version
of the motherboard is installed in the Rainbow system. The code to determine this is operating
system dependent. The examples in the following sections are written for CP/M, MS-DOS, and
Concurrent CP/M.

Example of Version Test for CP1M System
,.********************************************************************
*
pro c e d u r e
purpose:
restriction:
entry:
exit:

t e s t _ boa r d _ v e r s i o n

Test motherboard version
This routine will work under cp/m only.
none.
o = 'A' motherboard
flag :=
1 = 'B' motherboard
register usage: ax,bx,cx,dx,di,si,es

*
*

*
*
*

*
*

*
,.********************************************************************

5-2

Initialization and Control

d5eg
db
OOOh
r5
14
;re5erve 14 byte5
c5eg
te5t_board_ver5ion:
pU5h
bp
mov
ax,d5
;clear buffer, JU5t to be 5ure
mov
e5,ax
;point e5:di at it
mov
di,O
mov
cx,14
;14 byte5 to clear
xor
al,al
;clear clearing byte
buffer[dil,al
opt1:
mov
ido the clear
inc
di
loop
opt1
iloop till done
mov
ax,d5
ipoint bp:dx at buffer for
mov
; int 40 call
bp,ax
mov
dx,off5et buffer
di,1ah
mov
;5et opcode for call to get hw #
int
40
mov
5i,0
mov
cx,S
;5et count for P055ible return ASCII
buffer[5il,0
opt2:
cmp
;got 50mething back, have rainbow 'B'
opt3
Jne
inc
5i
; loop till done
loop
opt2
;no ASCII, 5et rainbow 'A' type
mov
flag,O
opt4
jmp
opt3:
mov
;got ASCII, 5et rainbow 'B' type
flag,1
opt4:
pop
bp
ret

flag
buffer

Example of Version Test for MS-DOS System
,.** •• * ••• * •••••••••••• **** ••••••• **** •• ** •• *** •••••••• ******** •••• *.*

•

pro c e d u r e

t e 5 t _ boa r d _ v e r 5 ion

•
•

te5t motherboard ver5ion
•
thi5 routine will work under MS-DOS only
•
-none
•
flag ••
o • 'A' motherboard
•
• 'B' motherboard
•
regi5ter u5age: ax,bx,cx,dx,di,5i
.*.*
••• ********* ••• *.*** ••• *** ••• **********.*************************
,
purpo5e:
re5triction:
entry:
exit:

•

5-3

Initialization and Control

cseg

segment byte
publIc 'codesg'
publIc test_board_version
assume cs:cseg,ds:dseg,es:dseg,ss:nothing

test_board_version
near
proc
;save bp
push
bp
dI,O
;clear buffer to be sure
mov
mov
cx,14
;14 bytes to clear
xor
al,al
;clear clearIng byte
tb1:
mov
byte ptr buffer[dll,al ;do the clear
inc
di
loop
tb1
; loop till done
ax,ds
mov
;point bp:dx at buffer for
mov
bp,ax
; I nt 18h call
mov
dx,offset buffer
mov
di,1ah
;set opcode for call to get hw #
18h
int
lint 40 remapped to 18h under MS-DOS
mov
si,O
mov
cx,8
;set count for possible return ASCII
tb2:
cmp
byte ptr buffer£sil,O
tb3
;got something back, have rainbow 'B'
jne
Inc
si
tb2
loop
flag,O
;no ASCII, set rainbow 'A' type
mov
tb4
jmp
tb3:
mov
flag,1
;got ASCII, set rainbow B type
;recover bp
tb4:
bp
pop
ret
test_board_version
endp
c5eg
end5
dseg
segment byte
public 'data5g'
public flag
0
fhg
db
buffer db
14
dup (?)
ends
d5eg
end

(
5-4

Initialization and Control

Example of Version Test for Concurrent CP1M System
,•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
pro c e d u r e

test motherboard vers10n
th1s rout1ne for Concurrent CP/M only
none
0
'A' motherboard
flag
1
'B' motherboard
reg1ster usage: ax,bx,cx,dx,s1

purpose:
restr1ction:
entry:
ex1t:

,...................................................... -- .......... _
mov
mov
mov
mov
mov
mov
int
mov
mov
mov
mov
cmp
Jne
inc
mov
cmp
je
mov
cmp
je
mov
cmp
je

*
*
*
*

t est _ boa r d _ v e r s 1 0 n

control_b+2,ds
d1,offset b10sd
bx,3
[d1+bxl,ds
dx,offset b10sd
cl,32h
OeOh
flag,O
bx,6
si,offset array_14
al,'O'
[si+bxl,al
found_b
bx
al,'1'
[si+bxl,al
test_board_exit
al,'2'
[si+bxl,al
test_board_exit
al,'3'
[si+bxl,al
test_board_exit

*
*
*

..
*

;setup for function SO call
; function 50
;set flag for rainbow 'A'
;offset to array_14

;'0', could be a rainbow 'A'
;no, must be rainbow 'B'
;next number •.•
;can be e1ther 1 .••

; or 2 •••

lor 3 1f its a rainbow 'A'

5-5

Initialization and Control

found_b:
mov
flag,1
test_board_exit:
ret
dseg
biosd
db
dw
dw
control_b
dw
dw
dw
array_14
rs
flag
db
end

jits a rainbow 'B'

80h

offset control_b
0

4
0

offset array_14
14
0

Initialize the Graphics Option
Initializing the Graphics Option can be separated into the following three major steps:
• Reset the GDC to the desired display environment.
• Initialize the rest of the GDC's operating parameters.
• Initialize the Graphic Option's registers, buffers, and maps.

Reset the GDC
To reset the GDC, give the RESET command with the appropriate parameters followed by commands and parameters to set the initial environment. The RESET command is given by writing a
zero byte to port 57h. The reset command parameters are written to port 56h.
The GDC Reset Command parameters are the following:

Parameter

Value

Meaning

12h

The GDC is in graphics mode
Video display is noninterlaced
No refresh cycles by the GDC
Drawing permitted only during retrace

16h
30h

For medium resolution
For high resolution
The number of active words per line, less two. There are 24 (18h) active
words per line in medium resolution mode and 50 (32h) words per line in
high resolution mode.

5-6

Initialization and Control

Parameter

Value

Meaning

61h
64h

For medium resolution
For high resolution
The low-order five bits are the horizontal sync width in words less one
(medium res. HS=2, high res. HS=5). The high-order three bits are the
low-order three bits of the vertical sync width in lines (VS=3).

04h
08h

For medium resolution
For high resolution
The low-order two bits are the high-order two bits of the vertical sync
width in lines. The high-order six bits are the horizontal front porch
width in words less one (medium res. HFP=2, high res. HFP=3).

02h
03h

For medium resolution
For high resolution
Horizontal back porch width in words less one (medium res. HBP=3, high
res. HBP=4).

03h

Vertical front porch width in lines (VFP=3).

FOh

Number of active lines per video field (single field, 240 line display).

40h

The low-order two bits are the high-order two bits of the number of
active lines per video field. The high-order six bits are the vertical back
porch width in lines (VBP=16).

Initialize the GDC
Now that the CDC has been reset and the video display has been defined, you can issue the rest of
the initialization commands and associated parameters by writing to ports 57h and 56h respectively.
Start the CDC by issuing the START command (6Bh).
ZOOM must be defined; however, since there is no hardware support for the Zoom feature, program
a zoom magnification factor of one by issuing the ZOOM command (46h) with a parameter byte of
00.
Issue the WDAT command (22h) to define the type of Read/Modify/Write operations as word transfers - low byte, then high byte. No parameters are needed at this time because the CDC is not being
asked to do a write operation; it is only being told how to relate to the memory.

5-7

Initialization and Control

Issue the PITCH command (47h) with a parameter byte of 20h for medium resolution or 40h for
high resolution to tell the GDC that each scan line begins 32 words after the previous one for
medium resolution and 64 words after the previous one for high resolution. Note, however, that only
24 or 50 words are displayed on each screen line. The undisplayed words left unscanned are
unusable.
The GDC can simultaneously display up to four windows. The PRAM command defines the window
display starting address in words and its length in lines. The Graphics Option uses only one display
window with a starting address of 0000 and a length of 256 lines. To set this up, issue the PRAM
command (70h) with four parameter bytes of OO,OO,FO,OF.
Another function of the GDC's parameter RAM is to hold soft character fonts and line patterns to be
drawn into the bitmap. The Graphics Option, rather than using the PRAM for this purpose, uses the
external Character RAM and Pattern Generator. For the external hardware to work properly, the
PRAM command bytes 9 and 10 must be loaded with all ones. Issue the PRAM command (78h) with
two parameter bytes of FF ,FF.
Issue the CCHAR command (4Bh) with three parameter bytes of 00,00,00, to define the cursor
characteristics as being a non-displayed point, one line high.
Issue the VSYNC command (6Fh) to make the GDC operate in master sync mode.
Issue the SYNC command (OFh) to start the video refresh action.
The GDC is now initialized.

Initialize the Graphics Option
First you must synchronize the Graphics Option with the GDC's write cycles. Reset the Mode
Register by writing anything to port SOh and then load the Mode Register.
Next, load the Scroll Map. Wait for the start of a vertical retrace, enable Scroll Map addressing,
select the Scroll Map, and load it with data.
Initialize the Color Map with default data kept in a shadow area. The Color Map is a write-only area
and using a shadow area makes the changing of the color palette more convenient.
Set the Pattern Generator to all ones in the Pattern Register and all ones in the Pattern Multiplier.
Set the Foreground/Background Register to all ones in the foreground and all zeros in the
background.
Set the ALU IPS Register to enable all four planes and put the option in REPLACE mode.
Finally, clear the screen by setting the entire bitmap to zeros.

5-8

Initialization and Control

Example of Initializing the Graphics Option
The following example is a routine that will initialize the Graphics Option including the GDC. This
initialization procedure leaves the bitmap cleared to zeros and enabled for writing but with graphics
output turned off. Use the procedure in the next section to turn the graphics output on. Updating of
the bitmap is independent of whether the graphics output is on or off.

,.********************************************************************
p r 0 c e d u r e
purpo5e:

n i t - 0 P t i 0 n

initialize the graphic5 option

dx = 1
medium re50lution
dx = 2
high re50lution
exit:
all 5hadow byte5 initialized
regi5ter u5age: none, all regi5ter5 are 5aved
entry:

*
*
*
*
*
*
*
*
*

,.********************************************************************
c5eg
extrn

5egment byte
public 'code5g'
alup5:near,pattern_regi5ter:near,pattern_mult:near,fgbg:near
public init_option
a55ume c5:c5eg,d5:d5eg,e5:d5eg,55:nothing
init_option
proc
near
pU5h
ax
;5ave the regi5ter5
bx
pU5h
pU5h
cx
pU5h
dx
di
pU5h
pU5h
5i
;make 5ure that 5t05 inC5.
c1d
jFir5t we have to find out what the interrupt vector i5 for the
;graphic5 option.
If th15 15 a Model 100-A, interrupt vector
;22h i5 the graphic5 interrupt.
If thi5 15 a Model 100-B, the
;interrupt vector i5 relocated up to A2.
If EEOO:OF44h and
;04(>0, we have the relocated vector5 of a Model 100-B and need
ito OR the m5b of our vector.
mov
mov
pU5h
mov
mov
mov
te5t
jz
mov

ax,d5
word ptr c5:5egment_5ave,ax
e5
;5ave valid e5
bx,OeeOOh
;te5t if vector5 are relocated
e5,bx
;100-A into vector ba5e addr
ax,88h
e5:byte ptr Of44h,4 ;relocated vector5?
gO
;jump if ye5
;100-B into vector ba5e addr
I!Ix,288h

\,
)

5-9

Initialization and Control

gO:

mov
pop
cmp
jz
jmp

word ptr g_int_vec,ax
es
dx,1
;medium resolution?
mid_res
;jump if yes
hi_res
;else is high resolution

mov
out
mov
call
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
mov
mov
mov
mov
jmp

al,OO
;medium resolution reset command
57h,al
gbmod,030h
;mode = med res, text, no readback
mode
;turn off graphics output
al,12h
;p1. refresh, draw enabled during
056h,al
;retrace
al,16h
;p2. 24 words/line minus 2
056h,al
;384/16 pixels/word=24 words/line
al ,61 h
;p3. 3 bits vs/5 bits hs width - 1
056h,al
;vs=3, hs=2
al,04
;p4. 6 bits hfp-1, 2 bits vs high
056h,al
;byte, 2 words hfp, no vs high byte
al,02
;p5. hbp-1, 3 words hbp
056h,al
al,03
;p6. vertical front porch, 3 lines
056h,al
al,OfOh
;p7. active lines displayed
056h,al
al,40h
;p8. 6 bits vbp/2 bits lines/field
056h,al
;high byte, vbp=16 lines
al,047h
;pitch command, med res, straight up
057h,al
al,32
;med res memory width for vert. pitch
056h,al
word ptr nmritl,3fffh
word ptr xmax,383
;384 pixels across in med res
byte ptr num_planes,4
;4 planes in med res
byte ptr shifts_per_Iine,5 ;rotates for 32 wds/line
byte ptr words_per_line,32 ;words in a line
common_init

mid_res:

5-10

(

Initialization and Control

hi_res: mov
out
mov
call
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
mov
mov
mov
mov
common_init:
mov
mov
mov
mov
out
mov
out
mov
out
mov
out

al,OO
;high resolution reset command
57h,al
gbmod,031h
;mode = high res, text, no readback
mode
;disable graphics output
al,12h
;p1. refresh, draw enabled during
056h,al
;retrace
al,30h
;p2. 50 words/line - 2
056h,al
al,64h
;p3. hsync w-1=4(low 5 bits), vsync
056h,al
;w=3(upper three bits)
al,08
;p4. hor fp w-1=2(upper 2 bits),
056h,al
;vsync high byte = 0
al,03
; p5. hbp-1. 3 words hbp
056h,al
al,03
;p6. vertical front porch, 3 lines
056h,al
al,OfOh
;p7. active lines displayed
056h,al
al,40h
;p8. 6 bits vbp/2 bits lines per field
056h,al
;high byte. vbp=16 lines
al,047h
;pitch command, high res, straight up
057h,al
al,64
;high res pitch is 64 words/line
056h,al
word ptr nmritl,7fffh
word ptr xmax,799
;800 pixels across
byte ptr num_planes,2
;2 planes in high res
byte ptr shifts_per_line,6 ;shifts for 64 wds/line
byte ptr words_per_line,64 ;number of words/line
al,OO
startl,al
starth,al
al,06bh
057h,al
al,046h
057h,al
al,O
056h,al
al,22h
57h,al

;setup start window display for memory
;location 00
;start command
;start the video signals going
;zoom command
;magnification assumed to be 0
;setup R/M/W memory cycles for
;figure drawing

5-11

Initialization and Control

jlnitialize PRAM command. Start window at the address in startl,
jstarth. Set the window length for 256 lines. Fill PRAM parameters
j8 and 9 with all ones so GOC can do graphics draw commands without
jaltering the data we want drawn.
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
out
mov
out
xor
mov
out
mov
out
mov
out
mov
out
out
mov
out
mov
or
out
mov

al,070h
jissue the pram command, setup
057h,al
jGOC display
al,startl
jp1. display window starting address
056h,al
j low byte
al,starth
jp2. display window starting address
056h,al
jhigh byte
al,Offh
jp3. make window 256 lines
056h,al
al,Ofh
jp4. high nibble display line on
056h,al
iright, the rest = 0
al,078h
jissue pram command pointing to p8
057h,al
al,Offh
i f i l l pram with ones pattern
056h,al
056h,al
al,04bh
jissue the cchar command
057h,al
al,al
iinitialize cchar parameter bytes
cchp1,al
jgraphics cursor is one line, not
056h,al
jdisplayed, non-blinking
cchp2,al
056h,al
cchp3,al
056h,al
al,06fh
jvsync command
057h,al
050h,al
jreset the graphics board
al,Obfh
53h,al
al,byte ptr gbmod
jenable, then disable interrupts
al,40h
jto flush the interrupt hardware
51h,al
j latches
cx,4920
jwait for a vert sync to happen

5-12

Initialization and Control

loop
mov
out
mov
out
call
call
mov
ca 11
mov
call
mov
call
mov
call
mov
mov
mov
rep
mov
mov
mov
mov
mov
mov
mov
mov
out
mov
out
call
mov
mov
out
pop
pop
pop
pop
pop
pop
ret
iniLoption

g1 :

g1
al,Obfh
53h,al
al,byte ptr gbmod
51h,al
assert_colormap
inscrl
b 1,1
pattern_mult
bl,Offh
pattern_register
bl,OfOh
fgbg
bl,O
alups
di,offset p1
al,Offh
cx,16
stosb
al,O
gbmskl ,al
gbmskh,al
al,Offh
gdcml,al
gdcmh,al
word ptr curlO,O
ax,word ptr gbmskl
54h,al
al,ah
55h,al
setram
word ptr ymax,239
al,Odh
57h,al
si
di
dx
cx
bx
ax

;disable the interrupts

;load colormap
;initialize scroll map
;set pattern multiplier to 16-bl
;see example "pattern_mult"
;set pattern data of all bits set
;see example "pattern_register"
;enable all foreground registers
;see example "fgbg"
;enable planes 0-3, REPLACE logic
;see example "alups"
;fill the p table with ff's.

;enable all gb mask writes.

;set GDC mask bits

;set cursor to top screen left
;fetch ahd issue the graphics
;option text mask

;then set ram to p1 thru p16 data

;enable the display
;recover the registers

endp

5-13

Initialization and Control

,• • • • • • • • • • • • • • • • • • • • • F • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

•

,••
sub r 0 u t i n e s
g rap h i c s
•
,••
•
,•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
gsubs
publ1c
publ1c

proc near
setram,assert_colormap,gdc_not_busy,imode,color_int,scrol_int
cxy2cp,mode

,•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••

•

sub r

uti n e

a s s e r t _ c o l o r map

colormap is located at clmpda which is defined in
procedure "change_colormap"

•
•
•
•

•
clmpda • colormap to be loaded
entry:
exit:
none
register usage: ax,bx

•
•

•

,•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
assert_colormap:
cld
call

;make sure nothing's happening

;The graphics interrupt vector "giv" is going to be either 22h or
;A2h depending on whether this is a Model 100-A or a Model 100-8
;with relocated vectors. Read the old vector, save it, then
;overwrite it with the new vector.
push
xor
mov
mov
cli
mov
mov
mov
mov
mov
mov
mov
st!
pop
mov
or
call

5-14

es
aX,ax
es,ax
bx,word ptr g_int_vec

;fetch address of "giv"
;temp. disable interrupts
;read the old offset

ax,es:[bxl
word ptr old_int_off,ax
ax,es:[bx+21
;read the old segment
word ptr old_int_seg,ax
word ptr es:[bxl,offset color_int ;load new offset
ax,cs
es:[bx+21,ax
;load new int segment
;re-enable interrupts
es
byte ptr int_done,O
;clear interrupt flag
byte ptr gbmod,40h
;enable graphics interrupt
mode

Initialization and Control

!!IC 1 :

te!!t
jz
pu!!h
xor
mov
mov
cli
mov
mov
mov
mov
st!
pop
cld
ret
color_int:
push
push
push
push
push
mov
mov
mov
cld
and
call
mov
mov
out
mov
c i 1:
lodsb
out
loop
mov
pop
pop
pop
pop
pop
iret

byte ptr int_done,Offh
!!Ic1

;h!!l!! interrupt routine run?
;re!!tore interrupt vector!!

!!IX ,!!IX
e!!,!!Ix
bx,word ptr g_int_vec

;fetch gr!!lphic!! vector off!!et

!!Ix,word ptr old_int_off ;re!!tore old interrupt vector
e!!dbxl,ax
ax,word ptr old_int_!!eg
e!!: [bx+2l ,ax

;m!!lke lods inc !!i

cx
ax
ax,word ptr cs:segment_!!ave ;can't depend on e!! or d!!
ds,ax
;reload segment registers
eS,ax
byte ptr gbmod,Obfh
;dlsable graphics interrupts'
mode
si,offset clmpda
;fetch color source
al,Odfh
;get the color map's attention
053h,al
cx,32
;32 color map entries
;fetch current color map data
051h,al
;load color map
ci1
;loop until all color map data loaded
byte ptr int_done,Offh ;set "interrupt done" flag
ax
cx
sl
ds
es

5-15

Initialization and Control

,.********************************************************************
sub r

u t

n e

Y2 c P

*
*
*

CXY2CP takes the xinit and yinit numbers, converts them to
an absolute memory location and puts that location into
curlO,1,2.
yinit is multiplied by the number of words per
line.
The lower 4 bits of xinit are shifted to the left
four places and put into curl2. xinit is shifted right four
places to get rid of pixel information and then added to
yinit times words per line.
This result becomes curIO,
curl1.

*
*

*
*
*
*
*

*
xinit
x pixel location
yinit
y pixel location
exit:
curIO,1,2
register usage: ax,bx,cx,dx
entry:

*
*
*

,-********************************************************************
cxy2cp: mov
mov
shl
mov
mov
mov
shl
mov
mov
shr
add
mov
ret

ax,yinit
;compute yinit times words/line
ax,cl
;ax has yinit times words/line
bx,xinit
;calculate the pixel address
dx,bx
;save a copy of xinit
cl,4
;shift xinit 4 places to the left
bl,cl
;bl has pixel within word address
curl2,bl
;pixel within word address
cl,4
;shift xinit 4 places to right
dx,cl
;to get xinit words
ax,dx
word ptr curlO,ax
;word address

,-********************************************************************
*
g d c _ n o t _ bus Y
sub r 0 u t
n e
*
*
gdc_not_busy will put a harmless command into the GDC and
wait for the command to be read out of the command FIFO.
This means that the GDC is not busy doing a write or read
operation.

*
*

*
entry:
none
exit:
none
register usage: ax

*
*
*

-********************************************************************
,

5-16

Initialization and Control

gdc_not_busy:
push
in
test
j z
mov
gnbO:
in
test
j z
loop
gnb2:
mov
out
in
test
j z
mov
gnb3:
in
test
jnz
loop
gnb4:
mov
out
mov
gnb5:
in
test
jnz
loop
gnbS:
pop
ret

cx
al,05Sh
al,2
gnb2
cx,BOOOh
al,05Sh
al,2
gnb2
gnbO
al,Odh
057h,al
al,05Sh
al,2
gnb4
cx,BOOOh
al,05Sh
al,2
gnb4
gnb3
ax,40dh
057h,al
cx,BOOOh
al,05Sh
ah,al
gnbS
gnb5
cx

juse cx as a time-out loop counter
jflrst check if the FIFO is full
jjump if not
jwait for FIFO not full or reasonable
jtime, whichever happens first
jhas a slot opened up yet?
j jump if yes
jtf loop count exceeded, go on anyway
jissue a screen-on command to GDC
jdid that last command fill it?
j jump if not
jread status register
jtest FIFO full bit
j jump if FIFO not full
jloop until FIFO not full or give up
jissue another screen-on,
jwait for FIFO empty
jread the GDC status
jFIFO empty bit set?
jjump if not.

,.********************************************************************
sub r

uti n e

i mod e

issue Mode command with the parameters from register gbmod
entry:
gbmod
exit:
none
register usage: ax

*
*
*
*
*

*
*
*

,.********************************************************************
imode:

call
mov
out
mov
out
ret

gdc_not_busy
al,Obfh
53h,al
al,gbmod
51h,al

jaddress the mode register through
jthe indirect register
jload the mode register

5-17

Initialization and Control

mode:

mov
out
mov
out
ret

IIl,Obfh
53h,al
al,gbmod
51h,al

;address the mode register through
;the indirect register
; load the mode register

,•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
sub r

uti n e

ins c r 1

initialize the scroll map
entry:
none
exit:
none
register usage: ax,bx,cx,dx,di,si

•
•
•
•
•
•
•
•

,•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
inscrl: cld
mov
xor
mov
inscO: stosb
inc
loop

cx,256
;initialize all 256 locations of the
al,al
;shadow area to desired values
di,offset scrltb
III

inscO

;The graphiCS interrupt vector is going to be either 22h or A2h
;depending on whether this is a Model 100-A or a Model 100-8 with
;relocated vectors. Read the old vector, save it, and overwrite it
;with the new vector. Before we call the interrupt, we need to
;make sure that the GDC is not writing something out to the bitmap.
ascrol: call
push
xor
mov
mov
cli
mov
mov
mov
mov
mov
mov
mov
sti
pop
mov
or
call

5-18

;check if GDC id busy
aX,ax
es,ax
bx,word ptr g_int_vec
;temporarily disable interrupts
ax,es:[bxl
;read the old offset
word ptr old_int_off,ax
ax,es:[bx+21
;read the old segment
word ptr old_int_seg,ax
word ptr es:[bxl,offset scrol_int ;load new offset
ax,cs
es:[bx+21,ax
;load new interrupt segment
ire-enable interrupts
es
byte ptr int_done,O
;clear interrupt flag
byte ptr gbmod,40h
;enable graphiCS interrupt
mode

Initialization and Control

in1 :

te!!t
jz
pu!!h
xor
mov
mov
cli
mov
mov
mov
mov
st!
pop
ret

byte ptr int_done,Offh ;ha!! interrupt routine run?
a!!1
;re!!tore the interrupt vector!!
aX,ax
e!!,ax
bx,word ptr g_int_vec ;fetch graphiC!! vector off!!et
ax,word ptr old_int_off ;re!!tore old interrupt vector
e!!:[bxl,ax
ax,word ptr old_int_!!eg
e!!:[bx+21,ax

;Scrollmap loading during interrupt routine.
;Fetch the current mode byte and enable scroll map addre!!!!ing.
!!crol_int:
push
pu!!h
pu!!h
push
push
pu!!h
cld
mov
mov
mov
and
mov
mov
and
call
mov
out
mov
xor
mov
mov
te!!t
jnz
!!hr

es
d!!
!!i
dx
cx
ax
ax,word ptr cs:segment_!!ave ;can't depend on ds
d!!,ax
;reload it
e!!,ax
byte ptr gbmod,Obfh
;disable graphic!! interrupts
al,gbmod
;prepare to acce!!!! !!croll map
gtemp1,al
;first !!ave current gbmod
gbmod,Odfh
;enable writing to scroll map
mode
;do it
al,07fh
;!!elect !!croll map and re!!et !!croll
53h,al
;map address counter
dl,51h
;output port de!!tination
dh,dh
si,offset scrltb ;first line's high byte address-O
cx,16
;256 line!! to write to
;high re!!olution?
byte ptr gbmod,1
ins1
;jump if yes
cx,1
;only 128 lines if medium resolution

5-19

Initialization and Control

in51:

5-20

lod5w
out
mov
out
lod5w
out
mov
out
lod5w
out
mov
out
lod5w
out
mov
out
lod5w
out
mov
out
lod5w
out
mov
out
lod5w
out
mov
out
lod5w
out
mov
out
loop
mov
mov
call
mov
pop
pop
pop
pop
pop
pop
iret

dx,al
al,ah
dx,al
dx,al
al,ah
dx,al
dx,al
al,ah
dx,al
dx,al
al,ah
dx,al
dx,al
al,ah
dx,al
dx,al
al,ah
dx,al
dx,al
al,ah
dx,al

;fetch two 5crollmap location5
;a55ert the even byte
;a55ert the odd byte
;fetch two 5crollmap location5
;a55ert the even byte
ja55ert the odd byte
;fetch two 5crollmap location5
;a55ert the even byte
;a55ert the odd byte
;fetch two 5crollmap location5
;a55ert the even byte
;a55ert the odd byte
;fetch two 5crollmap location5
;a55ert the even byte
;a55ert the odd byte
;fetch two 5crollmap location5
;a55ert the even byte
;a55ert the odd byte
;fetch two 5crollmap location5
;a55ert the even byte
;a55ert the odd byte
;fetch two 5crollmap location5
;a55ert the even byte

dx,al
aI, ah
dx,al
;a55ert the odd byte
in51
al,gtemp1
;re5tore previou5 mode regi5ter
gbmod,al
mode
byte ptr int_done,Offh ;5et interrupt-done flag
ax
cx
dx
5i

d5
e5
;return from interrupt

Initialization and Control

,.********************************************************************
sub r

uti n e

s e t ram

set video ram to a value stored in the p table
entry:
16 byte p1 table
exit:
none
register usage: ax,bx,cx,dx,di,si

*
*
*
*
*
*
*
*

,.********************************************************************
setram: mov
call
mov
out
out
mov
mov
setr1:
lodsb
out
loop
mov
out
out
mov
out
mov
out
mov
out
mov
out
mov
out
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
out
ret

byte ptr twdir,2 ;set write direction to the right
gdc_not_bu5y
;make sure that the GOC isn't busy
al,Ofeh
;select the write buffer
053h,al
;reset the write buffer counter
051h,al
si,offset p1
;initialize si to start of data
;load 16 chars into write buffer
cx,10h
;fetch byte to go to write buffer
52h,al
setr1
al,Ofeh
;select the write buffer
053h,al
051h,al
;reset the write buffer counter
al,049h
;issue GOC cursor location command
57h,al
al,byte ptr curIO ;fetch word location low byte
56h,al
;load parameter
al,byte ptr cur11 ;fetch word location high byte
;load parameter
56h,al
al,4ah
;set the GOC mask to all F's
57h,al
al,Offh
56h,al
56h,al
;i5sue figs command
al,04ch
57h,al
al,byte ptr twdir ;direction to write.
56h,al
al,nmritl
;number of GOC writes, low byte
56h,al
;number of GOC writes, high byte
al,nmrith
56h,al
;wdat command
al,22h
57h,al
;p1 and p2 are dummy parameters
al,Offh
;the GOC requires them for internal
56h,al
;purposes - no effect on the outside
56h,al

5-21

Initialization and Control

segment_save
dw
o
;ds save area for interrupts
gsubs
endp
cseg
ends
dseg
segment byte
public 'datasg'
extrn
clmpda:byte
public xmax,ymax,alu,d,d1,d2,dc
public curIO,curI1,curI2,dir,fg,gbmskl,gbmskh,gbmod,gdcml,gdcmh
publiC nmredl,nmredh,nmritl,nmrith,p1,prdata,prmult,scrltb,startl
public gtemp3,gtemp4,starth,gtemp,gtemp1,gtemp2,twdir,xinit,xfinal
public yinit,yfinal,ascrol,num_planes,shifts_per_line
public words_per_line,g_int_vec
;variables to be remembered about the graphics board states
alu
cchp1
cchp2
cchp3
curIO
curl1
curl2
dc
d
d2
d1
dir
fg
gbmskl
gbmskh
gbmod
gdcml
gdcmh

5-22

db
db
db
db
db
db
db
dw
dw
dw
dw
db
db
db
db
db
db
db

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

;current ALU state
;cursor/character
size definition
parameter bytes
;cursor
- low byte
location
- middle byte
storage
- high bits & dot address
;figs command dc parameter
;figs command d parameter
;figs command d2 parameter
;figs command d1 parameter
;figs direction.
;current foreground register
;graphics board mask register - low byte
- high byte
;graphics board mode register
;GDC mask register bits - low byte
- high byte

Initialization and Control

g_int_vec
gtemp
dw
gtemp1 db
gtemp2 db
gtemp3 db
gtemp4 db
int_done
nmredl db
nmredh db
nmritl db
nmrith db
num_plane5
old_int_5eg
old_inLoff
p1
db
prdata db
prmult db
5crltb db
5i_temp dw
5tartl db
5tarth db
twdir
db
5hift5_per_Iine
word5_per_line
xinit
dw
yinit
dw
xfinal dw
yfinal dw
xmax
dw
ymax
dw
d5eg
end

dw
0
;graphic5 option'5 interrupt vector
0
;temporary 5torage
0
;temporary 5torage
0
;temporary 5torage
0
;temporary 5torage
0
;temporary 5torage
db
o ;interrupt-done 5tate
0
;number of read operation5 - low byte
0
- high byte
;number of GDC write5 - low byte
0
0
- high byte
db
o ;number of plane5 in current re50lution
dw
o ;old interrupt 5egment
o ;old interrupt off5et
dw
16 dup (?) ;5hadow write buffer & GDC parameter5
0
;pattern regi5ter data
0
;pattern regi5ter multiplier factor
100h dup (?) ;5croll map 5hadow area
0
0
;regi5ter for 5tart addre55 of di5play
0
0
;direction for text mode write operation
db
0 ;5hift factor for one line of word5
db
0 ;word5/5can line for current re50lution
0
;x initial p05ition
0
;y initial p05itlon
0
;x final p05ition
0
;y flnal p05ition
0
0
end5

5-23

Initialization and Control

Controlling Graphics Output
There will be occasions when you will want to control the graphics output to the monitors. The
procedure varies according to the monitor configuration. The following two examples illustrate how
graphics output can be turned on and off in a single monitor system. The same procedures can be
used to turn graphics output on and off in a dual monitor system. However, in a dual monitor
configuration, you may want to display graphics output only on the color monitor and continue to
display VTI02 VSS text output on the monochrome monitor. This can be accomplished by loading an
83h into OAh instead of an 87h.

Example of Enabling a Single Monitor
,.********************************************************************
*
pro c e d u r e

9 rap h i c s _

*
purpose:

enable graphics output on single
color monitor

gbmod contalns mode register shadow byte
entry:
exit:
none
register usage: ax

*
*
*
*
*

,.********************************************************************
dseg
extrn
dseg
cseg
extrn

segment byte
public 'datasg'
;defined in procedure 'init_option'
gbmod:byte
ends
segment byte
public 'codesg'
imode:near
;defined in procedure 'init_option'
public graphics_on
assume cs:cseg,ds:dseg,es:dseg,ss:nothing

graphics_on
mov
out
or
call
ret
graphics_on
cseg
ends
end

5-24

proc
near
al,87h
Oah,al
;enable graphics on monochrome line
byte ptr gbmod,OBOh ;enable graphics output in gbmod
imode
;assert new mode register
endp

Initialization and Control

Example of Disabling a Single Monitor
.********************************************************************
,

pro c e d u r e
purpose:

9 rap h i c s _

f f

disable graphics output to single
(color> monitor

entry:
gbmod contains mode register shadow byte
exit:
none
register usage: ax

*
*
*
*
*
*
*

*
,.********************************************************************
dseg
extrn
dseg
cseg
extrn

segment byte
public 'datasg'
gbmod:byte
;defined in procedure 'init_option'
ends
segment byte
public 'codesg'
imode:near
;defined in procedure 'init_option'
public graphics_off
assume cs:cseg,ds:dseg,es:dseg,ss:nothing

graphics_off
and
call
mov
out
ret
graphics_off
cseg
ends
end

proc
near
byte ptr gbmod,07fh ;disable graphics output in gbmod
imode
;assert new mode register
al,83h
Oah,al
;turn off graphics on monochrome line
endp

Modifying and Loading the Color Map
For an application to modify the Color Map, it must first select the Color Map by way of the Indirect
Register (write DFh to port 53h). This will also clear the Color Map Index Counter to zero so
loading always starts at the beginning of the map.
Loading the Color Map is done during vertical retrace so there will be no interference with the
normal refreshing of the bitmap. To ensure that there is sufficient time to load the Color Map, you
must catch the beginning of a vertical retrace. First, check for vertical retrace going inactive (bit 5
of the GDC Status Register = 0). Then, look for the vertical retrace to start again (bit 5 of the GDC
Status Register = 1).

5-25

Initialization and Control

To modify only an entry or two, the use of a shadow color map is suggested. Changes can first be
made anywhere in the shadow map and then the entire shadow map can be loaded into the Color
Map. The next section is an example of modifying a shadow color map and then loading the data
from the shadow map into the Color Map.

Example of Modifying and Loading Color Data in a
Shadow Map
.**************************.******.**********************************
,

*
pro c e d u r e
purpose:
entry:

c han g e __ c

l o r map

change a color in the colormap
ax • new color (0 • highest intensity>
(F • lowest intensity>
al • high nibble • red data
low nibble
green data
ah
high nibble
gray data
low nibble
blue data
bx
palette entry number

exit:
register usage:

·
·
·

none
ax,bx,si

*
*
*
*
*
*
*
*
*
*
*

*
*

,.********************************************************************
cSII!g

segment
extrn
publiC
assume

byte
publiC 'codesg'
assert_colormap:near ;defined in 'init_option'
change_colormap
cs:cseg,ds:dseg,es:dseg,ss:nothing

change_colormap proc
near
mov
si,offset clmpda ;colormap shadow
mov
[si+bxl,al
;store the red and green data
add
bx,16
;increment to gray and blue data
mov
[si+bxl,ah
;store the gray and blue data
call
assert_colormap
;defined in 'init_option'
chenge_colormap endp
ends
segment byte
public 'datasg'
clmpda

5-26

Initialization and Control

;Colormap5:

;--------;Information in the Color Map i5 5tored a5 16 byte5 of red and
;green data followed by 16 byte5 of monochrome and blue data.
;For each color entry, a 0 5pecifie5 full inten5ity and Ofh
;5pecifie5 zero inten5ity.
;A 5ample 5et of color map entrie5 for a Model 100-8 5y5tem with
;a monochrome monitor in medium re50lution (16 5hade5> would look
;a5 follow5 in the 5hadow area labelled CLMPDA:
no red or green data
; clmpda

db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh

monochrome data, no blue data
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

Offh
OOfh
01fh
02fh
03fh
04fh
OSfh
06fh
07fh
08fh
09fh
Oafh
Obfh
Ocfh
Odfh
Oefh

;black
;white

;light monochrome

;medium monochrome

;dark monochrome

5-27

Initialization and Control

jOn a Model 100-A 5Y5tem, only the lower two bit5 of the monochrome
jnibble are 5ignificant. Thi5 allow5 only four monochrome 5hade5
ja5 opp05ed to 16 5hade5 on the Model 100-8 5y5tem in medium
jre50lution mode.
The following 5ample 5et of data applie5 to both
jthe Model 100-A monochrome-only 5y5tem in either medium or high
jre50lution mode, a5 well a5 the Model 100-8 monochrome-only 5y5tem
jin high re50lution mode.

jno red or green data
j clmpda

db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh

jmonochrome data, no blue data
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

5-28

Offh
OOfh
OSfh
Oafh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh

jblack
jwhite
jlight monochrome
jdark monochrome
jblack
jblack
jblack
jblack
jblack
jblack
jblack
jblack
jblack
jblack
jblack
jblack

Initialization and Control

;In a dual monitor configuration, with a Model 100-8 system in
;medium resolution mode, all four components of each color entry
;are present: red, green, blue and monochrome. A sample set of
;color data would be as follows:
;red and green data
;clmpda

db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

Offh
OOOh
OfOh
OOfh
OOOh
OOfh
Offh
OfOh
Oaah
Of8h
08fh
088h
08fh
Offh
Of8h
077h

;black
;white
;cyan
;magenta
;yellow
;red
;blue
;green
;dk gray
;dk cyan
;dk magenta
;dk yellow
;dk red
;dk blue
;dk green
;gray

;monochrome and blue data
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

Offh
OOOh
010h
020h
03fh
04fh
050h
06fh
07ah
Of8h
098h
Oafh
Obfh
Oc8h
Odfh
Oe7h

;black
;white

; light mono.

;med. mono.

;dark mono.

black
white
cyan
magenta
yellow
red
blue
green
dk gray
dk cyan
dk magenta
dk yellow
dk red
dk blue
dk green
gray

5-29

Initialization and Control

iOn a Model 100-A dual monitor configuration, in medium re501ution
;mode, all 16 color entrie5 are di5playable.
However, only two
;bit5 of monochrome data are available allowing for only 4
;monochrome 5hade5.
iOn a Model 100-A dual monitor configuration, in high re501ution
;mode, there are four di5playable color5 and again, four monochrome
;5hade5.
iOn a Model 100-B dual monitor configuration, in high re501ution
;mode, there al50 are four di5playable color5 and four monochrome
;5hade5.
;In a color monitor only 5Y5tem, the green data mU5t be mapped
ito the monochrome output.
For a Model 100-B 5ingle color monitor
;5Y5tem, in medium re501ution mode, a 5ample color map would be a5
;5hown below:
HOTE
The following 5ample color map will be
a55embled with thi5 example.
If thi5
i5 not appropriate, 5ub5titute one of
the other 5ample5 or generate one that
i5 cU5tom tailored to the application.

ired data, green data mapped to mono.
clmpda

5-30

db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

·Offh
OOfh
Offh
OOfh
OOfh
OOfh
Offh
Offh
Oafh
Offh
OBfh
OBfh
OBfh
Offh
Offh
07fh

;black
;white
;cyan
;magenta
;yellow
ired
;blue
;green
;dk gray
;dk cyan
;dk magenta
;dk yellow
;dk red
;dk blue
; dk green
;gray

Initialization and Control

;green dati!l, blue data
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

Offh
OOOh
OOOh
OfOh
OOfh
Offh
OfOh
OOfh
Oaah
OBBh
OfBh
OBfh
Offh
OfBh
OBfh
077h

;black
;white
;cyan
;magenta
;yellow
;red
;blue
;green
;dk gray
;dk cyan
;dk magenta
;dk yellow
;dk red
;dk blue
;dk green
;gray

;For a Model 100-A 5ingle color monitor 5Y5tem, in either high or
;medium re50lution mode, only the lower two bit5 of the monochrome
;output are 5ignificant.
Therefore, you can only di5play four
;inten5itie5 of green 5ince the green data mU5t be output through
;the monochrome line. The 5ame applie5 to a Model 100-B 5ingle
;color monitor 5y5tem in high re50lution mode.

d5eg

end5
end

5-31

6
Bitmap Write Setup (General)

Loading the ALU IPS Register
The ALU/PS Register data determines which bitmap planes will be written to during a
Read/Modify/Write (RMW) cycle and also sets the operation of the logic unit to one of three write
modes.
Bits 0 through 3 enable or disable the appropriate planes and bits 4 and 5 set the writing mode to
REPLACE, COMPLEMENT, or OVERLAY. Bits 6 and 7 are not used. Bit definitions for the
ALU/pS Register are in Part III of this manual.
Write an EFh to port 53h to select the ALU/pS Register and write the data to port 5Ih.

Example of Loading the ALUjPS Register
,.********************************************************************
*
pro c e d u r e

a I ups

*
*

purpose:

set the ALU/PS register

*
entry:
bl = value to set ALU/PS register to
exit:
update ALU/PS shadow byte
register usage: ax,

*
*

,.********************************************************************

6-1

Bitmap Write Setup

dseg
extrn
dseg
cseg

segment byte
public 'datasg'
alu:byte
ends
segment byte
publiC 'codesg'
extrn
gdc_not_busy:near
public alups
assume cs:cseg,ds:dseg,es:dseg,ss:nothing

alups

proc
call
mov
out
mov
mov
out
ret
endp
ends
end

alups
cseg

near
gdc_noLbusy
al,Oefh
53h,al
byte ptr alu,bl
al,bl
51h,al

;defined in procedure 'init_option'
;select ALU/PS register
;update shadow byte (alu)
;move new ALU/PS value to al
;load new value into ALU/PS register

loading the Foreground/Background Register
The data byte in the Foreground/Background Register determines whether bits are set or cleared in
each of the bitmap planes during a bitmap write (RMW) operation. Bit definitions for the Foreground/Background Register are in Part III of this manual.
Write an F7h to port 53h to select the Foreground/Background Register and write the data byte to
port 51h.

Example of Loading the Foreground/Background Register
,.********************************************************************

•

pro c e d u r e

9 b 9

•
•

purpose:

set the foreground I background register

entry:
bl = value to set fgbg register to
exit:
update fgbg shadow byte
register usage: ax

•
•
•
•

•

.********************************************************************

•

6-2

Bitmap Write Setup

dseg
extrn
dseg
cseg

segment
fg:byte
ends
segment
extrn
public
assume

byte

fgbg

proc
call
mov
out
mov
mov
out
ret
endp
ends
end

near
gdc_not_busy
al,Of7h
53h,al
byte ptr fg,bl
al,bl
51h,al

fgbg
cseg

public

'datasg'

byte
public 'codesg'
gdc_not_busy:near
fgbg
cs:cseg,ds:dseg,es:dseg,ss:nothing

;defined in 'init_option'
;select the foreground/background
register
;update shadow byte with new value
;load new value into fgbg register

6-3

7
Area Write Operations

This chapter contains examples that illustrate displaying 64K bytes of memory, and clearing a rectangular area of the screen to a given color.

Display Data from Memory
In the following example, video data in a 64K byte area of memory is loaded into the bitmap in order
to display it on the monitor. The last byte of the memory area specifies the resolution to be used. A
value of zero means use medium resolution mode. A value other than zero means use high resolution
mode. In medium resolution mode, the 64K bytes are written to four planes in the bitmap; in high
resolution mode, the 64K bytes are written to two planes.

Example of Displaying Data from Memory
,.********************************************************************

*
pro c e d u r e
purpose:

restore a graphics screen save in a 64k
segment of main memory by the procedure
ritvid.

*
*

*
*
*

,.********************************************************************

7-1

Area Write Operations

dseg
segment byte
publiC 'datasg'
extrn
gbmod:byte,gtemp:word,num_planes:byte,curlO:byte,gtemp1:byte
dseg ends
vldseg segment byte
public 'vseg'
extrn
vlddata:byte
vidseg ends
cseg
segment byte
public 'codesg'
extrn
init_option:near,fgbg:near,gdc_not_busy:near,alups:near
extrn
imode:near
public ri tvid
assume cs:cseg,ds:dseg,es:dseg,ss:nothing
ritvid

proc

near

;The video data is in vidseg. The last byte in vidseg is the
;resolution flag.
If flag is-O the option is in medium resolution
;mode; otherwise it is in high resolution mode.
Initialize the
;option to that resolution.

r t 1:
rt2:

mov
mov
call
mov
mov
mov
mov
test
lnz
mov
Jmp
mov
mov
mov
call

aX,es
word ptr cs:segment_save,ax
;save es
gdc_noLbusy
;wait till GDC is free
ax,vidseg
;set es to point to video buffer
eS,ax
si,Offffh
;fetch the resolution flag from
al,es:[sil
the last byte of vidbuf
al,Offh
; is it high resolution?
rt1
; jump i f yes.
dx,1
rt2
dx,2
ax,word ptr cs:segment_save
eS,ax
;restore old es
init_option
;assert the new resolution.

;init-option leaves us in text mode with fg-fO and alups-O.

rt3:

7-2

and
or
call
mov
call
test
jnz
mov
jmp
mov

byte ptr gbmod,Ofdh
byte ptr gbmod,010h
imode
;make sure we're in text mode
bl,Ofh
;put 1's into bg and O's into fg
;because write buffer inverts data
fgbg
byte ptr gbmod,1
;high resolution?
rt3
; jump if yes.
word ptr gtemp,1024 ;8 wrd-writes/plane (med res)
rt4
word ptr gtemp,2048 ;8 wrd-writes/plane (high res)

Area Write Operations

rt4:

mov
mov
mov
mov
xor

dl,O
jstart at beginning of vidbuf.
ax,vidseg
jset es to point to video buffer
es,ax
jfetch number of planes
cl,byte ptr num_planes
ch,ch
to be written

jEnable a plane to be written.
rt5:

mov
mov
sub
mov
mov
rol
and
call

jsave plane writing counter
word ptr gtemp1,cx
bl,byte ptr num_planes jselect plane to write enable
jthis is plane to write enable
bl,cl
cl,bl
bl,Ofeh
jput a 0 in that plane's select position
bl,cl
bl,Ofh
j keep in REPLACE mode
jassert the new ALU/PS
alups

jFill that plane with data, 8 words at a time, from vidseg.

rt6:

rt7:

mov
mov
push
call
mov
out
out
mov
mov
inc
out
loop
mov
out
mov
out
mov
out
mov
out
mov
out
out
xor
out
out
mov
out
mov

word ptr curl0,O
cx,word ptr gtemp
cx
gdc_not_busy
al,Ofeh
53h,al
51h,al
ex,16
al,es:[di1
di
52h,al
rt7
al,49h
57h,al
ax,word ptr curIO
56h,al
aI, ah
56h,al
al,04ah
57h,al
al,Offh
56h,al
56h,al
al,al
54h,al
55h,al
al,4ch
57h,al
al,2

jstart write at top left
jnumber of 8 word writes
to fill plane
jwait until GDC has finished
previous write

jfetch 16 bytes
jfill ptable with data
to be written

jassert the position to
start the write

jinit the mask to Offffh

jnow start the write
jdirection is down

7-3

Area Write Operations
\

out
mov
out
xor
out
mov
out
mov
out
out
add
pop
loop
mov
loop
mov
mov
ret
ritvld endp
segment_save
cseg
ends
end

56h,al
;do B writes
al,7
56h,al
al,al
56h,al
;start the write
al,22h
57h,al
al,Offh
56h,al
56h,al
;next location to be written
word ptr curlO,OB
cx
;loop to complete this plane
rt6
cx,word ptr gtemp1
;keep looping until all
planes are wrltten
rt5
ax,word ptr cs:segment_save
es,ax

Set a Rectangular Area to a Color
The example that follows illustrates how to set a rectangular area of the screen to some specified
color. Input data consists of the coordinates of the upper left and lower right corners of the area (in
pixels) plus the color specification (a 4-bit index value). The special case of setting the entire screen
to a specified color is included in the example as a subroutine that calls the general routine.

Example of Setting a Rectangular Area to a Color
,.********************************************************************
*
set _ a I I _ s c r e e n
pro c e d u r e
*
purpose:

set entire screen to a user defined color

entry:
exit:
register usage:

di is the color to clear the screen to
fgbg and alups shadow bytes updated
ax,bx,cx,dx,si,di

*
*

,.********************************************************************
cseg
extrn

7-4

segment byte
publiC 'codesg'
fgbg:near,gdc_not_busy:near,imode:near,alups:near
public set_all_screen,5et_rectangle
assume cs:cseg,ds:dseg,es:nothing,ss:nothing

Area Write Operations

mov
mov
mov
mov
mov
mov
jmp
set_alI_screen

near
word ptr xstart,O
word ptr ystart,O
ax,word ptr xmax
word ptr xstop,ax
ax,word ptr ymax
word ptr ystop,ax
set_rectangle
endp

istart at the top left corner

ifetch the bottom right corner
icoordinat.es.

.********************************************************************
,

*
set _ r e c tan g I e

pro c e d u r e
purpose:

set a user defined screen rectangle to a
user defined color

entry:

xstart has the start x in pixels
ystart has the start y in scan lines
xstop has the stop x in pixels
ystop has the stop y in scan lines
di is the color to clear the screen to

exit:
register usage:

*
*

*
*
*
*
*

*
*

ax,bx,cx,dx,di,si,xstart is altered
*
,.********************************************************************
set_rectangle

proc

near

iNo validity checks are being made on start and stop coordinates.
xstart must be
ystart must be

xstop
ystop

iAssert the new screen color to both nibbles of the the foregroundl
Put the option into REPLACE mode with all
ibackground register.
iplanes enabled and in write-enabled word mode.
mov
mov
mov
shl
or
call
xor
call
and
or
call

idi has the colori only low nibble valid
bx,di
bh,bl
icombine color number into both fg and bg
cl,4
ishift the color up to the high nibble
bh,cl
icombine high nibble with old low nibble
bl,bh
iassert new vaiue to fgbg register
fgbg
bl,bl
iset up REPLACE mode, all planes
iassert new value to ALU/PS register
alups
jset up text mode
byte ptr gbmod,Ofdh
jset up write enable mode
byte ptr gbmod,10h
jassert new value to mode register
imode

7-5

Area Write Operations

;Do the rectangle write.
;Do the write one column at a time. Since the GDC i5 a word device,
;we have to take into account that we might have our write window
;5tart on a pixel that i5n't on a word boundary. The graphic5
;option5 write ma5k mU5t be 5et accordingly. Do a write buffer
;write to all of the rectangle a5 defined by 5tart,5top. Calculate
;the fir5t curiO. Calculate the number of 5can5 per column to be
;written.
mov
mov
5hr
mov
mov
5hl
add
mov
mov
5ub
mov

ax,word ptr x5tart ;turn pixel addre55 into
cl,4
word addre55
ax,cl
dx,word ptr y5tart ;turn 5can start to word5/1ine*y
cl,byte ptr shifts_per_line ;number of shifts
dx,cl
dx,ax
;combine x and y word addre55es
word ptr curlO,dx
;fir5t curiO.
ax,word ptr y5tOp
;5ubtract start from 5tOp.
ax,word ptr ystart
word ptr nmrltl,ax

;Program the text mask.
;There are four P05sible write condition5a b c d -

partially write disabled to left
completely write enabled
partially di5abled to the right
partially di5abled to both left and right

;The portion to be write disabled to the left will be the current
;xstart pixel information. A5 we write a column, we update the
;current x5tart location. Only the flr5t x5tart will have a left
;hand portion write di5abled. Only the last will have a right
;hand portion disabled.
If the first is also the last, a portion
;of both side5 will be di5abled.

c151:

7-6

mov
mov
and
5hr

bx,Offffh
;calculate the current write ma~k
cx,word ptr x5tart
;eliminate all but pixel information
cx,Ofh
bx,cl
;shift in a
for each left pixel
to be disabled

Area Write Operations

;Write buffer write is done by columns.
Take the current xstart
;and use it as the column to be written to.
When the word address
;of xstart is greater than the word address of xstop, we are
;finished.
There is a case where the current word address of
;xstop is equal to the current word address xstart.
In that
;case we have to be concerned about write disabling the bits to
;the right.
When xstop becomes less than xstart then we are done.
mov
and
mov
and
cmp
jb
je
jmp

ax,word ptr xstart
ax,OfffOh
cx,word ptr xstop
cx,OfffOh
ax,cx
cls3
cls2
exit

;test if word xstop is equal
to word xstart

;below?
;jump if yes
;jump if equal
do last write
;all done - exit

;We need to set up the right hand write disable.
This is also the
;last write.
bx has the left hand write enable mask in it.
;Preserve and combine with the right hand mask which will be
;(f-stop pixel address> bits on the right.
cls2:

mov
and
inc
mov
shr
xor
and

cx,word ptr xstop
cx,Ofh
cx
ax,Offffh
ax,cl
ax,Offffh
bx,ax

;strip pixel info out of xstop
;make endpoint inclusive of write
;shift the disable mask
;wherever there is a one, we
;want to enable writes
;combine right and left masks

;bx currently has the mask bytes in it.
Where we have a one, we
;want to make a zero so that particular bit will be write enabled.
cls3:

xor

bx,Offffh

;Assert the new write mask,
;before we change the mask.
cls4:

call
mov
out
mov
out

gdc_not_busy
al,bh
55h,al
al,bl
54h,al

;invert to get zeros for ones
Make sure that the GDC is not busy

;check that the GDC isn't busy
;assert the upper write mask
;assert the lower write mask

;Position the GDC at the top of the column to be written.
This
;address was calculated earlier and the word need only be fetched
;and applied.
The number of scans to be written has already been
;calculated.

7-7

Area Write Operations

mov
out
mov
out
mov
out

al,49h
57h,al
ax,word ptr curIO
56h,al
al,dh
56h,al

ja55ert the GDC cur50r addre55
ja55ert word addre55 low byte
ja55ert word addre55 hiSh byte

jStart the write operation. Textma5k, alup5, sbmod and fSbS are
jalready 5et up. GDC i5 p05itioned.
mov
out
xor
out
mov
out
mov
out
mov
out
mov
out
out

al,4ch
ja55ert fiS5 to GDC
57h,al
al,al
jdirection 15 down
56h,al
ax,word ptr nmritl
ja55ert number of write
56h,al
al,ah
operation5 to perform
56h,al
ja55ert wdat
al,22h
57h,al
al,Offh
56h,al
56h,al

jUpdate the 5tartins x coordinate for the 5tart of the next
jcolumn write. Strip off the pixel information and then add 16
jpixe15 to it to set the next word addre55.
word ptr x5tart,OfffOh
and
j5tr1p off pixel info
word ptr x5tart,16
jaddre55 the next word
add
word ptr curIO
inc
jcheck for another column to clear
c151
jmp
exit:
ret
5et_rectansle
endp
end5
c5eS
public 'data5S'
5esment byte
d5eS
extrn
curlO:word,sbmod:byte,xmax:word,ymax:word
5hift5_per_line:byte
extrn
publiC x5tart,x5top,Y5tart,Y5top
x5tart dw
dw
x5tOP
y5tart dw
dw
y5tOp
nmritl dw
end5
d5eS
end

°
°
°
°
°

7-8

8
Vector Write Operations

The examples in this chapter illustrate some basic vector write operations. They cover setting up the
Pattern Generator and drawing a single pixel, a line, and a circle.

Setting Up the Pattern Generator
When operating in Vector Mode, all incoming data originates from the Pattern Generator. The
Pattern Generator is composed of a Pattern Register and a Pattern Multiplier. The Pattern Register
supplies the bit pattern to be written. The Pattern Multiplier determines how many times each bit is
sent to the bitmap write circuitry before being recirculated.

NOTE
The Pattern Multiplier must be loaded before loading the Pattern Register.

Example of Loading the Pattern Register
The Pattern Register is an 8-bit register that is loaded with a bit pattern. This bit pattern, modified
by a repeat factor stored in the Pattern Multiplier, is the data sent to the bitmap write circuitry
when the option is in Vector Mode.

8-1

Vector Write Operations

,.********************************************************************
*
pro c e d u r e
pat t ern _ reg i 5 t e r
*
*
purpo5e:
5et the pattern regi5ter
*
*
entry:
bl = pattern data
*
exit:
update pattern regi5ter 5hadow byte
*
regi5ter u5age: ax
*
caution:
you mU5t 5et the pattern multiplier before *
5etting the pattern regi5ter
*
,.********************************************************************
;The pattern regi5ter contain5 a 16-bit pixel pattern that i5 written
;to the bitmap when the Graphic5 Option i5 in Vector Mode.
;Sample regi5ter value5 and corre5ponding pattern5 are:
regi5ter value

pattern output

Offh
Oaah
OfOh
Ocdh

11111111
10101010
11110000
11001101

;The above a55ume5 that the Pattern Multiplier ha5 been 5et to
;multiply the pattern by 1.
If the Pattern Multiplier had been 5et
;to multiply the pattern by 3, the above example5, when output to
;the bitmap would look a5 follow5:

d5eg
extrn
d5eg
c5eg

8-2

regi5ter value

pattern output

Offh
Oaah
OfOh
Ocdh

111111111111111111111111
111000111000111000111000
111111111111000000000000
111111000000111111000111

5egment byte
public
prdata:byte
end5
5egment byte
publiC Icode5g '
extrn
gdc_not_bu5y:near
publiC pattern_regi5ter
a55ume c5:c5eg,d5:d5eg,e5:d5eg,55:nothing

Vector Write Operations

near
pattern_register
proc
call
gdc_not_busy
;defined in 'init_option'
;select the pattern register
mov
al,Ofbh
out
53h,al
mov
byte ptr prdata,bl ;update shadow byte
mov
al,bl
51h,al
;load the pattern register
out
ret
pattern_register
endp
ends
cseg
end

Example of loading the Pattern Multiplier
The Graphics Option expects to find a value in the Pattern Multiplier such that sixteen minus that
value is the number of times each bit in the Pattern Register is repeated. In the following example,
you supply the actual repeat factor and the coding converts it to the correct value for the Graphics
Option .
,. ********************************************************************
*
pat t ern _ m u I t
pro c e d u r e
*
*
set the pattern multiplier
purpose:
*
*
bl = value to multiply pattern by (1 - 16) *
entry:
exit:
updated pattern multiplier shadow byte
register usage: ax,bx
caution:
you must set the pattern multiplier before
setting the pattern register

*
*
*
*

*
,.********************************************************************
dseg
extrn
dseg
cseg

segment byte
public 'datasg'
prmult:byte
ends
segment byte
public 'codesg'
extrn
gdc_not_busy:near
;defined in 'init_option'
public pattern_mult
assume cs:cseg,ds:dseg,es:dseg,ss:nothing

8-3

Vector Write Operations

pattern_mult
call
mov
dec
not

mov
out
mov
out
ret
pattern_mult
ends
cseg
end

proc
near
gdc_not_busy
;defined in 'init_option'
byte ptr prmult,bl ;update multiplier shadow byte
bl
;make bl zero relative
bl
;invert it - remember that pattern
;register is multiplied by 16 minus
;the multiplier value
al,Ofdh
;select the pattern multiplier
53h,al
al,bl
;load the pattern multiplier
51h,al
endp

Display a Pixel
The following example displays a single pixel at a location specified by a given set of x and y
coordinates. Coordinate position 0,0 is in the upper left corner of the screen. The x and y values are
in pixels and are positive and zero-based. Valid values are:
x = 0 - 799 for high resolution
o - 383 for medium resolution
y = 0 - 239 for high or medium resolution

Also, in the following example, it is assumed that the Mode, ALU IPS, and Foreground/Background
registers have already been set up for a vector write operation.

Example of Displaying a Single Pixel
,.********************************************************************
pro c e d u r e

x e

*
*

*
purpose:

draw a pixel

entry:

xinit
x location
yinit
y location
valid x values
0-799 high resolution
0-383 medium resolution
0-239 med. or high res.
valid y values

*
*
*
*

*
*
*

,.********************************************************************

8-4

Vector Write Operations

jDo a vector draw of one pixel at coordinates in xinit,yinit.
Assume
jthat the Graphics Option is already set up in terms of Mode Register,
jForeground/Background Register, and ALU/PS Register.
dseg
extrn
extrn
dseg
cseg

segment byte
public
'datasg'
gbmod:byte,curlO:byte,curll:byte,cur12:byte,xinit:word
yinit:word
ends
segment byte
publiC
'codesg'
extrn
cxy2cp:near,gdc_not_busy:near
public pixel
assume cs:cseg,ds:dseg,es:dseg,ss:nothing

pixel

proc
call
call
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
mov
out
ret
endp
ends
end

pixel
cseg

near
gdc_not_busy
jconvert x,y to a cursor position
cxy2cp
al,49h
jsend out the cursor command byte
57h,al
ax,word ptr curIO jassert cursor location low byte
56h,al
al,ah
jassert cursor location high byte
56h,al
al,byte ptr curl2 jassert cursor pixel location
56h,al
al,4ch
jassert the figs command
57h,al
al,02h
jline direction - to the right
56h,al
al,6ch
;tell GDC to draw pixel when ready
57h,al

Display a Vector
The example in this section will draw a line between two points specified by x and y coordinates
given in pixels. The valid ranges for these coordinates are the same as specified for the previous
example. Again it is assumed that the Mode, ALUjPS, and Foreground/Background registers have
already been set up for a vector write operation. In addition, the Pattern Generator has been set up
for the type of line to be drawn between the two points.

8-5

Vector Write Operations

Example of Displaying a Vector
,.********************************************************************
*
pro c e d u r e

v e c tor

*
purpose:

draw a vector

*
*

entry:

xinit = starting x location
yinit = starting y location
xfinal= ending x location
yfinal- ending y location
valid x values
o - 799 high resolution
o - 383 medium resolution
valid y values
o - 239 high or med. res.

*
*
*

exit:
register usage: ax

*
*
*
*

*
*

,.********************************************************************
dseg
extrn
extrn
extrn
dseg
cseg
extrn

vector

segment byte
public 'datasg'
curlO:byte,cur11:byte,cur12:byte,dc:word,d:word,d2:word
d1:word,dir:byte,xinit:word,yinit:word,xf1nal:word
yfinal:word,gbmod:byte,p1:byte
ends
segment byte
publiC 'codesg'
gdc_not_busy:near,cxy2cp:near
public vector
assume cs:cseg,ds:dseg,es:dseg,ss:nothing
near
proc

;Draw a vector.
;Assume the start and stop coordinates to be 1n xinit, yinit,
;xfinal, and yf1nal. The Foreground/Background, ALU/PS, Mode,
;and Pattern Registers as well as the GDC PRAM bytes and all other
;1ncidental requirements such as "gdc_not_busy" have been taken
;care of already. This routine positions the cursor, computes the
;draw direction, dc, d, d2, d1 and then 1mplements the actual figs
;and figd commands.
call
call
mov
out
mov
out
mov
out

8-6

gdc_not_busy
cxy2cp ;convert starting x,y to a cursor position
al,49h
;set cursor location from curlO,1,2
57h,al
;issue the GDC cursor location command
al,curlO
;fetch word - low address
56h,al
al,cur11
;fetch word - middle address
56h,al

Vector Write Operations

mov
out
mov
cmp
jnz
mov
cmp
jnz
mov
out
mov
out
mov
out
ret
v1:
mov
sub
jns
quad12: ne9
mov
sub
js
quad 1: cmp
jbe
oct2:
mov
jmp
mov
oct3:
jmp
quad2:
ne9
cmp
jae
oct4:
mov
jmp
octS:
mov
jmp
quad34: mov
sub
jns
quad3: ne9
cmp
jbe
oct6:
mov
jmp
oct7:
mov
jmp

al,cur12
;dot address (top 4 bit~)/hi9h address
S6h,al
ax,word ptr xinit ;start and stop points the same?
ax,word ptr xfinal ;jump if not
v1
ax,word ptr yinit
;mi9ht be - check the y's
ax,word ptr yfinal
v1
;jump if not
al,04ch ;write sin91e pixel - current vector write
OS7h,al ;can't handle a one pixel write
al,2
OS6h,al
ai, 06ch
OS7h,al
bx,yfinal
jcompute delta y
bx,yinit
jdelta y ne9ative now?
jjump if not (must be quad 3 or 4)
quad34
bx
jdelta y is ne9ative, make absolute
ax,xfinal
jcompute delta x
aX,xinit
jdelta x ne9ative?
quad2
jjump if yes
ax,bx
joctant 2?
oct3
jjump if not
p1,02
jdirection of write
vxind jabs(deltax»abs(deltay), independent axis-x-axis
p1,03
jdirection of write
vyind jabs(deltax)-<abs(deltay), independent axis-y-axis
ax
jdelta x is ne9ative, make absolute
ax,bx
joctant 4?
octS
jjump if not
p1,04
jdirection of write
vyind jabs(deltax)=<abs(deltay), independent axis-y-axis
p1,OS
jdirection of write
vxind jabs(deltax»abs(deltay), independent axis-x-axis
ax,xfinal
jcompute delta x
ax,xinit
quad4
jjump if delta x is positive
ax
jmake delta x absolute instead of ne9ative
ax,bx
joctant 6?
oct7
jjump if not
p1,06
jdirection of write
vxind jabs(deltax»abs(deltay), independent axis=x-axis
p1,07
jdirection of write
vyind jabs(deltax)<-abs(deltay), independent axis-y-axis

8-7

Vector Write Operations

guad4:
octO:
oct1:
vyind:
vxind:

vdo:

vdo 1 :

vector
cseg

8-8

cmp
jae
mov
jmp
mov
jmp
xchg
and
mov
push
shl
sub
and
mov
pop
push
sub
shl
and
mov
pop
shl
dec
and
mov
mov
out
mov
or
out
mov
mov
lodsb
out
loop
mov
out
ret
endp
ends
end

ax,bx
;octant O?
oct1
;jump if not
p1,0
;direction of write
vyind ;abs(deltax)<abs(deltay), independent axis=y-axis
p1,01
;direction of write
vxind ;abs(deltax)=>(deltay), independent axis=x-axis
ax,bx
;put independent axis in ax, dependent in bx
ax,03fffh
;limit to 14 bits
dc,ax
;dc=abs(delta x)
;save abs(delta y)
bx
bx,1
bx,ax
bx,03fffh
;limit to 14 bits
;d=2*abs(delta y)-abs(delta x)
d,bx
;restore (abs(delta y)
bx
;save abs(delta y)
bx
bx,ax
bx, 1
bx,03fffh
;limit to 14 bits
;d2=2*(abs(delta y)-abs(delta x»
d2,bx
bx
bx,1
bx
bx,03fffh
;limit to 14 bits
;d1=2*abs(delta y)-1
d1,bx
al,04ch
;issue the figs command
57h,al
al,08
;construct p1 of figs command
al,p1
56h,al
;issue a parameter byte
si,offset dc
cx,08
;issue the 8 bytes of dc,d,d2,d1
;fetch byte
56h,al
;issue to the GDC
vdo1
;loop until all 8 done
al,06ch
;start the drawing process in motion
57h,al
;by issuing figd

Vector Write Operations

Display a Circle
The example in this section will display a circle, given the radius and the coordinates of the center in
pixels. The code is valid only if the option is in medium resolution mode. If this code is executed in
high resolution mode, the aspect ratio would cause the output to be generated as an ellipse. As in
the previous examples, the option is assumed to have been set up for a vector write operation with
the appropriate type of line programmed into the Pattern Generator.

Example of Drawing a Circle
,.********************************************************************
*
pro c e d u r e

c i

r c 1 e

*
purpose:

draw a circle in medium resolution mode

*
*

entry:

xinit = circle center x coordinate (0-799)
yinit = circle center y coordinate (0-239)
radius = radius of the circle in pixels

*
*

caution:

This routine will only work in medium
resolution mode.
Due to the aspect ratio
of high resolution mode, circles appear
as ellipses.

*
*
*
*

,.********************************************************************
;Draw an circle.
;This routine positions the cursor, computes the draw direction, dc,
;d, d2, d1 and implements the actual figs and figd commands.
;The Mode Register has been set up for graphics operations, the write
;mode and planes select is set up in the ALU/PS Register, the
;Foreground/Background Register is loaded with the desired foreground
;and background colors and the Pattern Multiplier/Pattern Register is
;loaded.
In graphics mode, all incoming data comes from the Pattern
;Register.
We have to make sure that the GDC's PRAM 8 and 9 are all
;ones 50 that it will try to write all ones to the bitmap.
The
;external hardware intervene and put the pattern register's data
;into the bitmap.

8-9

Vector Write Operations

extrn
extrn
dseg
dc
d
d2
d1
dm
xad
yad
radius
dseg
cseg

circle

8-10

gbmod:byte,curIO:byte,curI1:byte,curI2:byte,xinit:word
yinit:word,dir:byte,shifts_per_line:byte
segment byte
public 'datasg'
public radius,xad,yad
dw
o
dw
o
dw
o
dw
o
dw
o
o
dw
dw
o
dw
o
ends
segment byte
public 'codesg'
gdc_not_busy:near
extrn
public circle
assume cs:cseg,ds:dseg,es:dseg,ss:nothing
proc
call
mov
out
mov
out
out

near
gdc_not_busy
al,78h
57h,al
al,Offh
56h,al
56h,al

mov
mov
mov
mov
inc
mul
mov
dec
mov
shl
mov

word ptr d1,-1
word ptr dm,O
bx,word ptr radius
ax,Ob505h
bx
bx
word ptr dc,dx
bx
word ptr d,bx
bx,1
word ptr d2,bx

;set
;set
;get
;get

mov
mov
mov
sub
mov
call
mov
call
call
mov
call

aX,word ptr xinit
word ptr xad,ax
ax,word ptr yinit
ax,word ptr radius
word ptr yad,ax
acvt
byte ptr dir,01h
avdo
acvt
byte ptr dir,06h
avdo

;get center x
;save it
;get center y
;subtract radius
;save it
;position cursor
;arc 1
;draw it
;position cursor
;arc 6
;draw it

;set pram bytes 8 and 9

figs d1 parameter
figs d2 parameter
radius
1/1.41

;set figs dc parameter
;~et

figs d parameter

;set figs d2 parameter

Vector Write Operations

mov
mov
mov
add
mov
call
mov
call
call
mov
call

ax,word ptr xinit
word ptr xad,ax
ax,word ptr yinit
ax,word ptr radius
word ptr yad,ax
acvt
byte ptr dir,02h
avdo
acvt
byte ptr dir,OSh
avdo

;get center x
;save i t
;get center y
;add in radiu5
;save it
;position cursor
;arc 2
;draw it
;po5ition cursor
;arc 5
;draw it

mov
sub
mov
mov
mov
call
mov
call
call
mov
call

ax,word ptr xinit
ax,word ptr radius
word ptr xad,ax
ax,word ptr yinit
word ptr yad,ax
acvt
byte ptr dir,03h
avdo
acvt
byte ptr dir,OOh
avdo

;get center x
;subtract radius
;5ave it
;get center y
;5ave it
;position cursor
;arc 3
;draw it
;po5ition cursor
;arc
;draw it

mov
add
mov
mov
mov
call
mov
call
call
mov
call
ret

ax,word ptr xinit
ax,word ptr radius
word ptr xad,ax
ax,word ptr yinit
word ptr yad, ax
acvt
byte ptr dir,07h
avdo
acvt
byte ptr dir,04h
avdo

;get center x
;add in the radiu5
jsave it
jget center y
jsave it
jposition cursor
jarc 7
jdraw it
jposition cursor
jarc 4
jdraw i t

jConvert the starting x,y coordinate pair into a cursor p05ition
jword value.

8-11

Vector Write Operations

acvt:

avdo:

avdo 1 :

circle
cseg

8-12

mov
xor
mov
shl
mov
mov
mov
div
add
mov
mov
mov
shl
mov
mov
out
mov
out
mov
out
mov
out
ret
call
mov
out
mov
or
out
mov
mov
mov
out
inc
loop
mov
out
ret
endp
ends
end

cl,byte ptr shifts_per_Iine ;set up for 32/16-bit
dx,dx
;math - clear upper 16 bit
ax,word ptr yad
ax,cl
bx,ax
;save lines * word/line
ax,word ptr xad ;compute number of words on last line
cx,16
;16 bits/word
cx
;ax has number of extra words to add in
ax,bx
;dx has the <16 dot address left over
curlO,al
;this is the new cursor memory address
curl1,ah
cl,04
;dot address is high nibble of byte
dl,cl
curl2,dl
a I, 49h
;set cursor location to curI0,1,2
57h,al
;issue the GDC cursor location command
al,curlO
;fetch word - low address
56h,al
al,curl1
;fetch word - middle address
56h,al
al,curl2
;dot address (top 4 bits)/high address
56h,al
gdc_not_busy
al,4ch
57h,al
al,020h
al,byte ptr dir
56h,al
si,offset dc
cx, 10
al,[sil
56h,al
si
avd01
al,6ch
57h,al

;issue the figs command
;construct p1 of figs command
;issue a parameter byte
;issue the 10 bytes of dc,d,d2,d1
;fetch byte
;issue to the GDC
;point to next in list
;loop until all 10 done
;start drawing process in motion
;by issuing figd

9
Text Write Operations

In this chapter the examples illustrate coding for writing byte-aligned 8 X 10 characters, determining type and position of the cursor, and writing bit-aligned vector (stroked) characters.

Write a Byte-Aligned Character
This example uses a character matrix that is eight pixels wide and ten scan lines high. The characters are written in high resolution mode and are aligned on byte boundaries. The inputs are the
column and row numbers that locate the character, the code for the character, and the color
attribute.

Example of Writing a Byte-Aligned Character
,.********************************************************************
*
pro c e d u r e

9 t ext

purpose:

write 8 pixels wide x 10 scan lines
graphics text in high resolution

entry:

ax
bx
dl
dh

*
*

*
*
*

is
is
is
is

the
the
the
the

column location of the character
row location of the character
character
fgbg

*
*

,.********************************************************************
dseg

segment byte

publiC

'datasg'

9-1

Text Write Operations

extrn

curlO:byte,cur12:byte,gbmod:byte,fg:byte

;This table has the addresses of the individual text font characters.
;Particular textab addresses are found by taking the offset of the
;textab, adding in the ASCII offset of the character to be printed
;and loading the resulting word. This word is the address of the
;start of the character's text font.
gbmskl
gbmskh
textab

9-2

db
db
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw

til

0
0
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
280
290
300
310
320
330
340
350
360
370

Text Write Operations

dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw

380
390
400
410
420
430
440
450
460
470
480
490
500
510
520
530
540
550
560
570
580
590
600
610
620
630
640
650
660
670
680
690
700
710
720
730
740
750
760
770
780
790
800
810
820
830
840
850

9-3

Text Write Operations
,

dIN
dIN
dIN
dIN
dIN
dIN
dIN
dIN
dIN

860
870
BBO
B90
900
910
920
930
940

jtext font
5pace

db
db
db
db
db
db
db
db
db
db

11111111b
Offh
Offh
Offh
Offh
Offh
Offh
Offh
Offh
11111111b

exclam

db
db
db
db
db
db
db
db
db
db

11111111b
11100111b
11100111b
11100111b
11100111b
11100111b
11111111b
11100111b
11111111b
11111111b

guote

db
db
db
db
db
db
db
db
db
db

11111111b
Od7h
Od7h
Od7h
Offh
Offh
Offh
Offh
Offh
11111111b

9-4

Text Write Operations

num

db
db
db
db
db
db
db
db
db
db

llllllllb
11010111b
11010111b
0000000lb
11010111b
0000000lb
11010111b
11010111b
llllll11b
lll11111b

dollar

db
db
db
db
db
db
db
db
db
db

ll111111b
11101111b
10000001b
01101111b
10000011b
11101101b
000000llb
11101111b
llllllllb
llllllllb

percent db
db
db
db
db
db
db
db
db
db

llllllllb
00111101b
00111011b
11110111b
11101111b
11011111b
10111001b
01111001b
lllll111b
l1111111b

amp

l1111111b
10000111b
01111011b
10110111b
11001111b
10110101b
01111011b
10000100b
lllll111b
lllll111b

db
db
db
db
db
db
db
db
db
db

9-5

Text Write Operations

apos

lefpar

ritpar

aster

9-6

11111111b

11100111b

11101111b

11011111b

11111111b

11110011b

11100111b

11001111b

11100111b

11110011b

11111111b

11001111b

11100111b

11110011b

11100111b

11001111b

11111111b

10111011b

11010111b

0OOOOOO1b

11010111b

10111011b

11111111b

Text Write Operations

plus

comma

minus

period

11111111b

db
db

11111111b
11101111b

11101111b

0OOOOOO1b

11101111b

11111111b

11100111b

11001111b

11111111b

0OOOOOO1b

11111111b

11100111b

11111111b

9-7

Text Write Operations

slash

db
db
db
db
db
db
db
db
db
db

11111111b
11111101b
11111001b
11110011b
11100111b
11001111b
10011111b
00111111b
11111111b
11111111b

zero

db
db
db
db
db
db
db
db
db
db

11111111b
11000101b
10010001b
10010001b
10001001b
10001':101b
10011001b
10100011b
11111111b
11111111b

one

db
db
db
db
db
db
db
db
db
db

11111111b
11100111b
11000111b
11100111b
11100111b
11100111b
11100111b
10000001b
11111111b
11111111b

two

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
11111001b
11100011b
11001111b
10011111b
10000001b
11111111b
11111111b

9-8

Text Write Operations

three

db
db
db
db
db
db
db
db
db
db

11111111b
10000001b
11110011b
11100111b
11000011b
11111001b
10011001b
11000011b
11111111b
11111111b

four

db
db
db
db
db
db
db
db
db
db

11111111b
11110001b
11100001b
11001001b
10011001b
10000001b
11111001b
11111001b
11111111b
11111111b

five

db
db
db
db
db
db
db
db
db
db

11111111b
10000001b
10011111b
10000011b
11111001b
11111001b
10011001b
11000011b
11111111b
11111111b

six

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
10011111b
10000011b
10001001b
10011001b
11000011b
11111111b
11111111b

9-9

Text Write Operations

5even

db
db
db
db
db
db
db
db
db
db

11111111b
10000001b
11111001b
11110011b
11100111b
11001111b
10011111b
10011111b
11111111b
11111111b

eight

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
10011001b
11000011b
10011001b
10011001b
11000011b
11111111b
11111111b

nine

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
10010001b
11000001b
11111 001 b
10011001b
11000011b
11111111b
11111111b

colon

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
11100111b
11100111b
11111111b
11100111b
11100111b
11111111b
11111111b

9-10

Text Write Operations

5colon

le55t

egual

greatr

11111111b

11100111b

11111111b

11100111b

11001111b

11111111b

11111001b

11110011b

11001111b

10011111b

11001111b

11110011b

11111001b

11111111b

10000001b

11111111b

10000001b

11111111b

10011111b

11001111b

11110011b

11111001b

11110011b

11001111b

10011111b

11111111b

9-11

Text Write Operations

9 ues

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
11111001b
11110011b
11100111b
11111111b
11100111b
11111111b
11111111b

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
10011001b
10010001b
10010011b
10011111b
11000001b
11111111b
11111111b

capa

db
db
db
db
db
db
db
db
db
db

11111111b
11100111b
11000011b
10011001b
10011001b
10000001b
10011001b
10011001b
11111111b
11111111b

capb

db
db
db
db
db
db
db
db
db
db

11111111b
10000011b
10011001b
10011001b
10000011b
10011001b
10011001b
10000011b
11111111b
11111111b

9-12

Text Write Operations

cape

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
10011111b
10011111b
10011111b
10011001b
11000011b
11111111b
11111111b

capd

db
db
db
db
db
db
db
db
db
db

11111111b
10000011b
10011001b
10011001b
10011001b
10011001b
10011001b
10000011b
11111111b
11111111b

cape

db
db
db
db
db
db
db
db
db
db

11111111b
10000001b
10011111b
10011111b
10000011b
10011111b
10011111b
10000001b
11111111b
11111111b

capf

db
db
db
db
db
db
db
db
db
db

11111111b
10000001b
10011101b
10011111b
10000111b
10011111b
10011111b
10011111b
11111111b
11111111b

9-13

Text Write Operations

cap9

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
10011001b
10011111b
10010001b
10011001b
11000011b
11111111b
11111111b

caph

db
db
db
db
db
db
db
db
db
db

11111111b
10011001b
10011001b
10011001b
10000001b
10011001b
10011001b
10011001b
11111111b
11111111b

capi

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
11100111b
11100111b
11100111b
11100111b
11100111b
11000011b
11111111b
11111111b

capj

db
db
db
db
db
db
db
db
db
db

11111111b
11100001b
11110011b
11110011b
11110011b
11110011b
10010011b
11000111b
11111111b
11111111b

9-14

Text Write Operations

capk

db
db
db
db
db
db
db
db
db
db

11111111b
10011001b
10010011b
10000111b
10001111b
10000111b
10010011b
10011001b
11111111b
11111111b

capl

db
db
db
db
db
db
db
db
db
db

11111111b
10000111b
11001111b
11001111b
11001111b
11001111b
11001101b
10000001b
11111111b
11111111b

capm

db
db
db
db
db
db
db
db
db
db

11111111b
00111001b
0OO10001b
00101001b
00101001b
00111001b
00111001b
00111001b
11111111b
11111111b

capn

db
db
db
db
db
db
db
db
db
db

11111111b
10011001b
10001001b
10001001b
10000001b
10010001b
10010001b
10011001b
11111111b
11111111b

9-15

Text Write Operations

db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
10011001b
10011001b
10011001b
10011001b
11000011b
11111111b
11111111b
11111111b
10000011b
10011001b
10011001b
10000011b
10011111b
10011111b
10011111b
11111111b
11111111b

capq

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
10011001b
10011001b
10010001b
10011001b
11000001b
11111100b
11111111b

capr

db
db
db
db
db
db
db
db
db
db

11111111b
10000011b
10011001b
10011001b
10000011b
10000111b
10010011b
10011001b
11111111b
11111111b

capo

capp

9-16

Text Write Operations

caps

db
db
db
db
db
db
db
db
db
db

11111111b
11000011b
10011001b
10011111b
11000111b
11110001b
10011001b
11000011b
11111111b
11111111b

capt

db
db
db
db
db
db
db
db
db
db

11111111b
10000001b
11100111b
11100111b
11100111b
11100111b
11100111b
11100111b
11111111b
11111111b

capu

db
db
db
db
db
db
db
db
db
db

11111111b
10011001b
10011001b
10011001b
10011001b
10011001b
10011001b
11000011b
11111111b
11111111b

capv

db
db
db
db
db
db
db
db
db
db

11111111b
10011001b
10011001b
10011001b
10011001b
10011001b
11000011b
11100111b
11111111b
11111111b

9-17

Text Write Operations

cap'"

db
db
db
db
db
db
db
db
db
db

11111111b
00111001b
00111001b
00111001b
00111001b
00101001b
0OOOOOO1b
00111001b
11111111b
11111111b

capx

db
db
db
db
db
db
db
db
db
db

11111111b
10011001b
10011001b
11000011b
11100111b
11000011b
10011001b
10011001b
11111111b
11111111b

eapy

db
db
db
db
db
db
db
db
db
db

11111111b
10011001b
10011001b
11000011b
11100111b
11100111b
11100111b
11000011b
11111111b
11111111b

capz

db
db
db
db
db
db
db
db
db
db

11111111b
10000001b
11111001b
11110011b
11100111b
11001111b
10011101b
10000001b
11111111b
11111111b

9-18

Text Write Operations

Ibrak

db
db
db
db
db
db
db
db
db
db

11111111b
10000011b
10011111b
10011111b
10011111b
10011111b
10011111b
10000011b
11111111b
11111111b

bslash

db
db
db
db
db
db
db
db
db
db

11111111b
10111111b
10011111b
11001111b
11100111b
11110011b
11111001b
11111101b
11111111b
11111111b

rbrak

db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

11111111b
10000011b
11110011b
11110011b
11110011b
11110011b
11110011b
10000011b
11111111b
11111111b
11111111b
11101111b
11010111b
10111011b
11111111b
11111111b
11111111b
11111111b
11111111b
11111111b

caret

9-19

Text Write Operations

underl

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
11111111b
11111111b
11111111b
11111111b
11111111b
11111111b
OOOOOOOOb

lsguot

db
db
db
db
db
db
db
db
db
db

11111111b
11100111b
11100111b
11110111b
11111111b
11111111b
11111111b
11111111b
11111111b
11111111b

lita

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
10000011b
11111001b
11000001b
10011001b
11000001b
11111111b
11111111b

litb

db
db
db
db
db
db
db
db
db
db

11111111b
10011111b
10011111b
10000011b
10011001b
10011001b
10011001b
10000011b
11111111b
11111111b

9-20

Text Write Operations

lite

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
11000011b
10011001b
10011111b
10011001b
11000011b
11111111b
11111111b

litd

db
db
db
db
db
db
db
db
db
db

11111111b
11111001b
11111001b
11000001b
10010001b
10011001b
10010001b
11000001b
11111111b
11111111b

lite

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
11000011b
10011001b
10000011b
10011111b
11000011b
11111111b
11111111b

litf

db
db
db
db
db
db
db
db
db
db

11111111b
11100011b
11001001b
11001111b
10000011b
11001111b
11001111b
11001111b
11111111b
11111111b

9-21

Text Write Operations

1 itg

lith

lit i

litj

9-22

11111111b

11111001b

11000001b

10010011b

11000011b

11110011b

10010011b

11000111b

11111111b

10011111b

10000011b

10001001b

10011001b

11111111b

11100111b

11111111b

11000111b

11100111b

10000001b

11111111b

11110011b

11111111b

11110011b

10010011b

11000111b

Text Write Operations

1it k

1 i tl

litm

litn

11111111b

10011111b

10010011b

10000111b

10010011b

10011001b

11111111b

11000111b

11100111b

11000011b

11111111b

10010011b

00101001b

00111001b

11111111b

10100011b

10001001b

10011001b

11111111b

9-23

Text Write Operations

lito

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
11000011b
10011001b
10011001b
10011001b
11000011b
11111111b
11111111b

litp

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
10100011b
10001001b
10011001b
10001001b
10000011b
10011111b
10011111b

litq

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
11000101b
10010001b
10011001b
10010001b
11000001b
11111001b
11111001b

litr

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
10100011b
10011001b
10011111b
10011111b
10011111b
11111111b
11111111b

9-24

Text Write Operations

lit5

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
11000001b
10011111b
11000011b
11111001b
10000011b
11111111b
11111111b

1it t

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11001111b
10000011b
11001111b
11001111b
11001001b
11100011b
11111111b
11111111b

I i tu

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
10011001b
10011001b
10011001b
10011001b
11000011b
11111111b
11111111b

litv

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
10011001b
10011001b
10011001b
11011011b
11100111b
11111111b
11111111b

9-25

Text Write Operations

litw

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
00111001b
00111001b
00101001b
10101011b
10010011b
11111111b
11111111b

1 itx

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
10011001b
11000011b
11100111b
11000011b
10011001b
11111111b
11111111b

lity

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
10011001b
10011001b
10011001b
11100001b
11111001b
10011001b
11000011b

litz

db
db
db
db
db
db
db
db
db
db

11111111b
11111111b
11111111b
10000001b
11110011b
11100111b
11001111b
10000001b
11111111b
11111111b

9-26

Text Write Operations

lsbrak

db
db

db
db
db
db
db
db
db
vert!

db
db
db
db
db
db
db
db
db
db

rsbrak

db
db
db
db
db
db
db
db
db
tilde

db
db

db
dseg
cseg
extrn
gtext

lllll111b
11110001b
11100111b
11001111b
10011111b
11001111b
11001111b
11100011b
l1111111b
l1111111b
lll11111b
11100111b
11100111b
11100111b
11100111b
11100111b
11100111b
11100111b
11100111b
llllll11b
l1111111b
10001111b
11100111b
11110011b
11111001b
11110011b
11100111b
10001111b
ll111111b
ll111111b
l1111111b
10011111b
01100101b
11110011b
l1111111b
llll1111b
l1111111b
ll111111b
l1111111b
ll111111b

ends
segment byte
public
'codesg'
public gtext
mode:near.gdc_not_busy:near
assume
cs:cseg.ds:dseg.es:dseg.ss:nothing
proc
near

9-27

Text Write Operations
\

;We are going to assume that the character is byte-aligned. Anything
;else will be ignored with the char being written out to the integer
;of the byte address.
;Special conditions: if dl=Offh - don't print anything.
;1)Make sure that the Graphics Option doesn't have any pending
;operations to be completed.
;2)Turn the x,y coordinates passed in ax,bx into a cursor word
;address to be saved and then asserted to the GDC.
;3)If the current foreground/background colors are not those
;desired, assert the desired colors to the Foreground/Background
;Register.
;4)Determine in which half of the word the character is to be
;written to and then enable that portion of the write.
;S)Check to see if the character we are being requested to print is
;legal. Anything under 20h is considered to be unprintable and so we
;just exit. We also consider Offh to be unprintable since the Rainbow
;uses this code as a delete marker.
;6)Turn the character's code into a word offset. Use this offset to
;find an address in a table. This table is a table of near addresses
;that define the starting address of the ten bytes that is the
;particular character's font. Fetch the first two bytes and assert to
;the screen. We have to assert write buffer counter reset because we
;are only using two of the words in the write buffer, not all 8.
;Each byte is loaded into both the left and right byte of a write
;buffer word. The GDC is programmed to perform the two-scan-line
;write and we wait for the write to finish. The next 8 scan lines
;of the character font are loaded into both the left and right bytes
;of the write buffer and these eight lines are then written to the
;screen.
push
call
pop

;Ax
the column number of the character. Bx is the row number.
;In high resolution, each bx is = 640 words
;Cursor position = (ax/2)+10*(bx*scan line width in words)
mov
shr
mov
shl
mov
mov
shl
add

9-28

di,ax
ax,1
cx,6
bx,cl
si,bx
cl,3
bx,cl
bx,si

;save the x so that we can check it later
;turn column position into a word address
;high resolution is 64 words per line
;bx*scan line length
;save a copy of scan times count
;to get bx*10 first multiply bx by 8
;then
;add in the 2*bx*scan line length

Text Write Operations

add
add
mov

bx,!ii
;thi!i give!i 10*bx*!ican line length
bx,ax
;combine x and y into a word addre!i!i
word ptr curlO,bx ;po!iition to write the word at

;A55ert the color5 attribute!i of the character to fgbg. Dh ha!i the
;foreground and background attribute!i in it.
cmp

JZ
mov
out
mov
mov
out

dh, byte ptr fg
cont
al,Of7h
53h,al
byte ptr fg,dh
al,dh
51h,al

; i!i the fgbg color the one we want?
; jump i f ye!i

;A5!iert the graphiC!i board'!i text ma!ik. The GDC doe!i 16-bit write!i
;in text mode but our character!i are only 8 bit!i wide. We mU!it enable
;half of the write and di5able the other half. If the x wa!i odd then
;enable the right half. If the x wa!i even then enable the left half.
cont:

odd:
com:

te!it
jnz
mov
jmp
mov
call

di,1
; i!i thi!i a fir!it byte?
odd
; jump i f not
word ptr gbm5k I, OOffh
com
word ptr gbm!ik I, OffOOh
!itgbm
;a!i!iert the graphic!i board ma5k

;Only the character!i below 127h are defined - the other!i are legal
;but not in the font table. After checking for a legal character
;fetch the addre55 entry (character number - 20h) in the table.
;Thi!i i5 the addre!i!i of the fir!it byte of the character'!i font.

contO:

cont1:

cmp
ja
Jmp
cmp
jnz
jmp
!iub
xor
mov
!ihl
mov

dl,1fh
contO
exit
dl,Offh
cont1
exit
dl,20h
dh,dh
bx,dx
bx,1
!ii,textab[bx]

;unprintable character?
; jump i f not
;don't print illegal character
; i!i thi!i a delete marker?
; jump i f not
;exit i f ye!i
;table !itart5 with a !ipace
; at 0
index off bx
;acce!i!i table
;byte to word addre!i!i off5et

;Textab ha5 the relative off5et!i of each character in it. All we have
;to do i!i add the !itart of the font table to the relative off5et of
;the particular character.

9-29

Text Write Operations

add

5i,off5et 5pace ;combine table off5et with
;character off5et

;Tran5fer the font from the font table into the write buffer.
;Write the fir5t two 5can5, then do the la5t 8.
c1d
mov
out
out
lod5w
out
out
mov
out
out
mov
out
out

al,Ofeh
53h,al
51h,al
52h,al
52h,al
al,ah
52h,al
52h,al
al,Ofeh
53h,al
51h,al

;make 5ure lod5b inC5 5i.
;re5et the write buffer counter

;fetch both byte5.
;put the byte into both 1 and 2
;write buffer byte5
;put the byte into both 1 and 2
;write buffer byte5
;re5et the write buffer counter

;Check to 5ee if already in text mode.

textm:

9-30

te5t
jz
and
call
mov
out
mov
out
mov
out
mov
out
mov
out
out
mov
out
xor
out
mov
out
xor
out

byte ptr gbmod,2
textm
; jump i f in text mode el5e
byte ptr gbmod,Ofdh
;a55ert text mode
mode
al,49h
;a55ert the cur50r command
57h,al
ax,word ptr curIO
56h,al
al,ah
56h,al
al,4ah
;a55ert the ma5k command
57h,al
al,Offh
56h,al
56h,al
al,4ch
;a55ert the fig5 command
57h,al
al,al
;a55ert the down direction to write
56h,al
al,1
;do it 2 write cycle5
56h,al
al,al
56h,al

Text Write Operations

mov
out
mov
out
out

al,22h
57h,al
al,Offh
56h,al
56h,al

;assert the wdat command

;Wait for the first two scans to be written.

here 1 :

mov
out
in
test
jz

ax,422h
57h,al
al,56h
ah,al
here1

;make sure the GDC isn't drawing
;write a wdat to the GDC
;read the status register
;did the wdat get executed?
; jump if not

;si is still pointing to the next scan line to be fetched. Get the
;next two scan lines and then tell the GDC to write them. No new
;cursor, GDC mask, graphics mask or mode commands need be issued.

ldcr:

exit:
stgbm:

gtext
cseg

mov
lodsb
out
out
loop
mov
out
xor
out
mov
out
mov
out
mov
out
mov
out
out
ret
mov
out
mov
out
ret
endp
ends
end

cx,8
52h,al
52h,al
ldcr
al,4ch
57h,al
aI, al
56h,al
ax,7
56h,al
al,ah
56h,al
a I, 22h
57h,al
al,Offh
56h,al
56h,al

;eight scan lines
;fetch the byte
;put the byte into both 1 and 2
;write buffer bytes
;assert the figs command
;assert the down direction to write
;do 8 write cycles

;assert the wdat command

ax,word ptr gbmskl
54h,al
aI, ah
55h,al

9-31

Text Write Operations

Define and Position the Cursor
There are two routines in the following example. One sets the cursor type to no cursor, block,
underscore, or block and underscore. It then sets up the current cursor location and calls the second
routine. The second routine accepts new coordinates for the cursor and moves the cursor to the new
location.

Example of Defining and Positioning the Cursor
,.********************************************************************
*
pro c e d u r e
9 set t y P
*
purpose:
entry:

assert new cursor type
dl bits determine cursor style
(if no bits set, no cursor is displayed>
block
bit
bit 1
undefined
undefined
bit 2
bit 3
underscore

*
*

*
*
*
*

*
*

;********************************************************************

dseg
extrn
block

segment byte
public
'datasg'
curlO:byte,cur12:byte,gbmod:byte
db
0,0,0,0,0,0,0,0,0,0

cdis
lastcl

db
dw
dw
db
dw

ocurs
newcl
ncurs
unders
userd
dseg

dw
db
db
db

°
°
0

°
°°
°Offh,Offh,Offh,Offh,Offh,Offh,Offh,Offh,O,Offh
0,0,0,0,0,0,0,0,0,0

ends

;Implements the new cursor type to be displayed. The current
;cursor type and location must become the old type and location.
;The new type becomes whatever is in dl.
This routine will fetch
;the previous cursor type out of NCURS and put it into OCURS and
;then put the new cursor type into NCURS.
The previous cursor
;coordinates are fetched and put into ax and bx.
A branch to
;GSETPOS then erases the old cursor and displays the new cursor.
;Cursor type bits are not exclusive of each other.
A cursor can
;be both an underscore and a block.

9-32

Text Write Operations

dl= 0
1

cseg
extrn

turns the cursor display off
displays the insert cursor (full block)
displays the overwrite cursor (underscore)
displays a simultaneous underscore and block cursor
public
'codesg'
segment byte
mode:near
assume cs:cseg,ds:dseg,es:dseg,ss:nothing
publiC gsettyp

gsettyp
mov
mov
mov
mov
mov
jmp
gsettyp endp

near
proc
al,byte ptr ncurs
byte ptr ocurs,al
byte ptr ncurs,dl
ax,word ptr newcl
bx,word ptr newcl+2
pos

;current cursor becomes
old cursor type
; pic k up new cursor type
; pick up current x and y
cursor coordinates
;branch to assert new cursor
type in old location

,-********************************************************************
*
pro c e d u r e
9 set p 0 s
*
*
assert new cursor position
purpose:
*
ax
x location
entry:
*
bx
y location
*
*

,.********************************************************************

gsetpos proc

publiC
near

gsetpos

;Display the cursor.
Cursor type was defined by GSETTYP.
The
;cursor type is stored in NCURS.
Fetch the type and address of the
;previous cursor and put it into OCURS and also into lastcl and
;lastcl+2.
If a cursor is currently being displayed, erase it.
If
;there is a new cursor to display, write it (or them) to the screen.
;A cursor may be a block or an underscore or both.
;The x and y coordinates of the cursor are converted into an address
;that the GDC can use.
Either the left or the right half of the text
;mask is enabled, depending on whether the x is even or odd. The
;write operation itself takes places in complement mode so that no
;information on the screen is lost or obscured but only inverted in
;value.
In order to ensure that all planes are inverted, a OfOh is
;loaded into the Foreground/Background Register and all planes are
;write enabled.
The cursor is written to the screen in two separate
;writes because the write buffer is eight, not ten, words long.

9-33

Text Write Operations

;Move current cursor type and location to previous type and location.

pos:

mov
mov
cld
mov
mov
mov
mov
mov
mov

cl,byte ptr ncurs
byte ptr ocurs,cl

;move current cursor type
into old cursor type

cx,word ptr newcl
word ptr lastcl,cx
cx,word ptr newcl+2
word ptr lastcl+2,cx
word ptr newcl,ax
word ptr newcl+2,bx

;move current cursor
location into old cursor
location
;save new cursor coordinates
;in new cursor location

;Before doing anything to the graphics option we need to make sure
;that the option isn't already in use.
Assert a harmless command
;into the FIFO and wait for the GDC to execute it.
call
;Set up the graphics option.
Put the Graphics Option in complement
;and text modes with all planes enabled.
Assert fgbg and text mask.
;Calculate the write address and store in curIO,1.
mov
out
mov
out

ax,10efh
53h,al
al,ah
51h,al

;address the ALU/PS
register
;set complement mode with
all planes enabled

;Assert text mode with read disabled.
mov
and
or
cmp
jz
mov
call
gsposO: mov
out
mov
out

al,byte ptr gbmod
al,Ofdh
al,10h
al,byte ptr gbmod
gsposO
byte ptr gbmod,al
mode
al,Of7h
53h,al
al,OfOh
51h,al

;get mode shadow byte
;set text mode
;set write enabled mode
;is mode already asserted
this way? If yes, jump
;update the mode register
;set Foreground/Background
register to invert data

;Is a cursor currently being displayed?
If cdis<>O, then yes. Any
;current cursor will have to be erased before we display a new one.
g!!lp01 :

test
jz

9-34

byte ptr cdis,1
gspos2

;if no old cursor to erase,
just display old one

Text Write Operations

;This part will erase the old cursor.
mov
mov
mov
call
call
test
jz
mov
call
gspos 1 : test
jz
call
mov
call

byte ptr cdis,O
dh,byte ptr lastcl
dl,byte ptr lastcl+2
asmask
dx2curl
byte ptr ocurs,8
gspos1
si,offset unders
discurs
byte ptr ocurs,1
gspos2
not_busy
;wait
si,offset block
discurs

;set no cursor on screen
;fetch x and y, put into dx,
and call dx2curl
;assert the mask registers
;turn dx into GDC address
;underline?
; jump i f not
;erase the underline
;do the write
;block?
; jump i f not
till done erasing underline
;erase the block
;do the write

;Write the new cursor out to the screen.
gspos2: cmp
jz
mov
mov
call
call
call
test
jz
mov
call
gspos3: test
jz
call
mov
call
gspos4: or
gspos5: call
ret

byte ptr ncurs,O
gspos5
dh,byte ptr newcl
dl,byte ptr newcl+2
not_busy
asmask
dx2curl
byte ptr ncurs,8
gspos3
si,offset unders
discurs
byte ptr ncurs,1
gspos4
not_busy
si,offset block
discurs
byte ptr cdis,1
not_busy

;write a new cursor?
;jump if not
;fetch coordinates of
new cursor
;wait for erase to finish
;assert the mask registers
;underscore cursor?
;jump i f not
;set up for underline cursor
;do the write
;block cursor?
;jump if not
;wait for any write to finish
;set up for block cursor
;do the write.
;set cursor displayed flag

;Enable one byte of the text mask.
asmask: mov
test
jz
mov
ritc4:
out
mov
out
ret

ax,OOffh
dh,1
ritc4
aX,OffOOh
55h,al
aI, ah
54h,al

;set up the text mask
;write to the right byte?
; jump if yes
;issue low byte of mask
;issue high byte of mask

9-35

Text Write Operations

jOisplay the cursor.
jAssume that the option is already set up in text mode, complement
jwrite and that the appropriate text mask is already set. The
jaddress of the cursor pattern is loaded into the si.
discurs:
mov
out
out
lodsb
out
out
lodsb
out
out
mov
out
out
mov
out
mov
out
mov
out
mov
out
mov
out
out
mov
out
xor
out
mov
out
xor
out
mov
out
mov
out
out
call
mov

9-36

al,Ofeh
53h,al
51h,al

jselect the write buffer and clear
the write buffer counter

52h,al
52h,al

jfeed the same byte to both halves
of the word to be written

52h,al
jfeed the same byte to both halves
52h,al
of the word to be written
jselect the write buffer and clear
al,Ofeh
53h,al
the write buffer counter
51h,al
jassert the position to write
al,49h
57h,al
ax,word ptr curIO
56h,al
al,ah
56h,al
jissue the GOC mask command to
al,4ah
57h,al
set all GOC mask bits
al,Offh
56h,al
56h,al
al,4ch
jprogram a write of ten scans
57h,al
first do two scans, then eight
al,al
56h,al
al,1
56h,al
al,al
56h,al
jstart the write
al,22h
57h,al
al,Offh
56h,al
56h,al
not_busy
jwait for first two lines to finish
cx,8
jthen write the next 8 scans

Text Write Operations

ritc6:

lodsb
out
out
loop
mov
out
xor
out
mov
out
xor
out
mov
out
mov
out
out
ret

;fetch the cursor shape
;feed the same byte to both halves
of the word

52h,al
52h,al
ritc6
al,4ch
57h,al
al,al
56h,al
al,7
56h,al
al,al
56h,al
al,22h
57h,al
al,Offh
56h,al
56h,al

;program a write of eight scans

;start the write

;Turn dh and dl into a word address (dl is the line and dh
;is the column).
Store the result in word ptr curIO.
Start with
;turning dl (line) into a word address.
Word address

dl * number of words/line * 10

;Turn dh (column) into a word address.
Word address = dh/2
;Combine the two.
;the GDC.

This gives the curIO address to be asserted to

dx2curl:

ritc5:

mov
mov
test
jz
inc
xor
shl
mov
mov
shl
shl
add
shr

aI, dh
;store the column count
;medium resolution = 32 words/line
c 1,5
;is it high resolution?
byte ptr gbmod,1
ritc5
;jump if not
cl
;high resolution = 64 words/line
dh,dh
dx,cl
bx,dx
;multiply dx by ten
c 1,3
bx, 1
dx,cl
dx,bx
;this is the row address
al,1
;this is the column number

9-37

Text Write Operations

xor
add
mov
ret

ah,ah
dx,ax
word ptr curlO,dx

;thi5 i5 the combined row and
;column addre55

;Thi5 i5 a qUicker ver5ion of GDC_NOT_BUSY.
We don't wa5te time on
;50me of the normal check5 and thing5 that GDC_NOT_BUSY doe5 due to
;the need to move a5 quickly a5 p055ible on the cur50r era5e/write
;routine5. Thi5 routine doe5 the 5ame 50rt of thing5. A harmle55
;command i5 i55ued to the GDC. If the GDC i5 in the proce55 of
;performing 50me other command, the WDAT we jU5t i55ued
;will 5tay in the GDC'5 command FIFO until 5uch time a5 the GDC can
;get to it. If the FIFO empty bit i5 5et, the GDC executed the
;WDAT command and mU5t be fini5hed with any previou5 operation5
;programmed into it.
not_bu5y:
mov
out
bU5y:
in
te5t
jz
ret
g5etp05 endp
c5eg
end5
end

aX,422h
57h,al
a I, 56h
ah,al
bU5y

;a55ert a WDAT
;wait for FIFO empty bit

Write a Text String
The example in this section writes a string of ASCII text starting at a specified location and using a
specified scale factor. It uses the vector write routine from Chapter 8 to form each character.

Example of Writing a Text String
;********************************************************************

*
pro c e d u r e

v e c tor _ t ext

*
*
entry:

cx = 5tring length
text = pointer to externally defined array of
ASCII character5
5cale
character scale
xinit
5tarting x location
yinit
5tarting y location

*
*

*
,.********************************************************************

9-38

Text Write Operations

c5eg

5egment
extrn
extrn
publiC
a55ume

byte
public 'code5g'
imode:near,pattern_mult:near,pattern_regi5ter:near
vector:near
vector_text
c5:c5eg,d5:d5eg,e5:d5eg,55:nothing

vector_text
proc
near
or
byte ptr gbmod,082h
;en5ure we're in graphic5 mode
call
imode
mov
al,4ah
out
57h,al
mov
al,Offh
out
56h,al
;enable GDC ma5k data write
56h,al
out
;enable all option ma5k write5
al,al
xor
out
55h,al
out
54h,al
mov
bl, 1
pattern_mult
;5et pattern multiplier
call
mov
bl,Offh
pattern_regi5ter
;5et pattern regi5ter
call
;get initial x
mov
ax,word ptr xinit
word ptr xad,ax
;5ave i t
mov
;get initial y
ax,word ptr yinit
mov
;5ave i t
word ptr yad,ax
mov
5i,off5et text
mov
dO_5tring:
;get character
lod5b
5i
pU5h
cx
pU5h
;di5play it
di5play_character
call
mov
ax,8
;move over by cell value
mov
cl,byte ptr 5cale
mul
cx
add
word ptr xad,ax
pop
cx
pop
5i
;loop until done
loop
ret
di5play_character:
;make 5ure we're in font table
cmp
aI, 07fh
jbe
char_cont_1
;continue if we are
ret
char_cont_1 :
;check if we can print character
al,20h
cmp
char_cont
;continue if we can
ja
ret

9-39

Text Write Operations

char_cont:
xor
ah,ah
shl
ax,1
mov
si,ax
mov
si,font_table[sil
get_next_stroke:
mov
ax,word ptr xad
mov
word ptr xinit,ax
mov
aX,word ptr yad
mov
word ptr yinit,ax
lodsb
al,endc
cmp
cont_1
jnz
ret
cont_1: mov
bx,ax
and
ax,Ofh
al,OSh
test
ct
jz
or
ax,OfffOh
ct:
mov
cl,byte ptr scale
xor
ch,ch
cx
push
cx
imul
sub
word ptr yinit,ax
and
bx,OfOh
shr
bx,1
bx,1
shr
bx,1
shr
shr
bx,1
test
bl,08h
jz
ct 1
or
bx,OfffOh
ct1:
mov
ax,bx
cx
pop
imul
cx
add
word ptr xinit,ax

9-40

;clear high byte
;make it a word pointer
;point si to font info

;get stroke info
lend of character?
;continue if not

;mask to y value
; negative?
;sign extend

;multiply by scale value
;subtract to y offset
;mask to x value
;shift to four least
significant bits

; negative ?
;sign extend
;recover scale
;multiply by scale value
;add to x offset

Text Write Operations

mov
ax,word ptr xad
mov
word ptr xfinal,ax
mov
ax,word ptr yad
mov
word ptr yfinal,ax
lod5b
cmp
al,endc
jz
di5play_char_exit
cmp
al, endv
jz
get_next_5troke
mov
bX,ax
and
ax,Ofh
te5t
a 1, 08h
jz
ct2
or
ax,OfffOh
ct2:
mov
cl,byte ptr 5cale
xor
ch,ch
pU5h
cx
imul
cx
5ub
word ptr yfinal,ax
and
bx,OfOh
5hr
bx,1
5hr
bx,1
5hr
bx,1
5hr
bX,1
te5t
bl,08h
jz
ct3
or
bx,OfffOh
ct3:
mov
ax,bx
cx
pop
imul
cx
add
word ptr xfinal,ax
pU5h
5i
call
vector
5i
pop
mov
ax,word ptr xfinal
mov
word ptr xinit,ax
mov
aX,word ptr yfinal
mov
word ptr yinit,ax
jmp
next_5troke
di5play_char_exit:
ret
vector_text
endp
c5eg
d5eg
extrn
extrn
public

j5et up xy off5et5

jget 5troke byte
jend of character ?
jye5 then leave
jdark vector ?
jye5, begin again
jma5k to y value
jnegative
j5ign extend
jget 5cale information

jmultiply by 5cale
j5ubtract to y off5et
jma5k to x value
j5hift to four lea5t
5ignificant bit5

jnegative ?
j5ign extend
jrecover 5cale
jmultiply by 5cale
jadd to x off5et
j5aVe index to font info
jdraw 5troke
jrecover font index
jend of 5troke become5
beginning of next 5troke

end5
5egment byte
public 'data5g'
gbmod:byte,xinit:word,yinit:word,xfinal:word,yfinal:word
xad:word,yad:word,text:byte
5cale

9-41

Text Write Operations

,.******************************************************************

,· *
,· *
·, *

5troke font character 5et

*
*
*

,.******************************************************************
;The following table5 contain vertex data for a 5troked character
;5et. The x and y coordinate information i5 repre5ented by 4-bit,
;25-complement number5 in the range of + or - 7. The x and y bit
;po5ition5 are a5 follow5:
bit

7 6 S 4 3 2 1 0
\

I
x

;End of character i5 repre5ented by the value x = -8, Y = -8.
;The dark vector i5 repre5ented by x = -8, Y = o.
;ASCII character5 are mapped into the p05itive quadrant, with the
;origin at the lower left corner of an upper ca5e character.
endc
endv

equ
equ

10001000b
10000000b

font_table

dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw

off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et

9-42

fonLOO
font_01
font_02
font_03
fonL04
fonLOS
fonL06
font_07
fonL08
fonL09
font_Oa
font_~b

font_Dc
font_Od
font_De
font_Of
font_10
font_11
font_12
fonL13
fonL14
font_1S

;end of character
;la5t vector of polyline

Text Write Operations

dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill

off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off~et

off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et
off5et

font_16
font_17
font_18
font_19
font_1a
fonL 1b
font_1c
font_1d
font_1e
font_1f
font_20
font_21
font_22
font_23
font_24
fonL25
fonL26
font_27
font_28
font_29
font_2a
fonL2b
font_2c
font_2d
font_2e
font_2f
font_30
fonL31
fonL32
fonL33
font_34
font_35
font_36
font_37
font_38
font_39
font_3a
fonL3b
font_3c
font_3d
font_3e
font_3f
fonL40
font_41
fonL42
fonL43

;5pace
•, I.

9-43

Text Write Operations

dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw
dw

9-44

offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset

font_44
font_45
font_4S
font_47
fonL48
font_49
font_4a
fonL4b
font_4c
fonL4d
font_4e
fonL4f
font_50
font_51
font_52
font_53
font_54
fonL55
font_5S
font_57
fonL58
fonL59
font_Sa
font_5b
font_5c
font_5d
font_5e
font_Sf
font_SO
fonLS1
font_S2
font_S3
font_S4
font_S5
font_SS
font_S7
font_S8
font_S9
font_Sa
font_Sb
font_Sc
font_Sd
font_Se
font_Sf
fonL 70
fonL71
font_72
font_73

Text Write Operations

fonLDD
font_D1
font_D2
font_D3
font_04
fonLDS
font_D6
fonLD7
fonLD8
fonLD9
font_Da
fonLDb
font_Dc
font_Dd
font_De
fonLOf
font_1D
font_11
fonL 12
fonL13
font_14
fonL1S
fonL16
fonL17
fonL 18
font_19
font_1a
fonL 1b
font_1c
fonL 1d
font_1e
font_1f
font_2D

dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill
dill

offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset
offset

db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc
endc

font_74
fonL7S
font_76
fonL77
fonL78
fonL79
font_7a
fonL7b
font_7c
fonL 7d
font_7e
font_7f

;space

9-45

Text Write Operations

font_21
font_22
font_23
font_24
font_25
font_26
font_27
font_28
fonL29
font_2a
font_2b
font_2c
font_2d
font_2e
font_2f
font_30
font_31
font_32
font_33
font_34
font_35
font_36
font_37
font_38
fonL39
font_3a
font_3b
font_3c
font_3d
font_3e
font_3f
font_40
font_41
font_42

9-46

db 20h,21h,endv,23h,26h,endc
db 24h,26h,endv,54h,56h,endc
db 20h,26h,endv,40h,46h,endv,04h,64h,endv,02h,62h
db endc
db 2fh,27h,endv,01h,10h,30h,41h,42h,33h,13h,04h,05h
db 16h,36h,045h,endc
db 11h,55h,endv,14h,15h,25h,24h,14h,endv,41h,51h,52h
db 42h,41h,endc
db 50h,14h,15h,26h,36h,45h,44h,11h,10h,30h,52h,endc
db 34h,36h,endc
db 4eh, 11h, 14h,47h,endc
db Oeh,31h,34h,07h,endc
db 30h,36h,endv,11h,55h,endv,15h,51h,endv,03h,63h
db endc
db 30h,36h,endv,03h,63h,endc
db 11h,20h,2fh,Odh,endc
db 03h,63h,endc
db OOh,01h,11h,10h,OOh,endc
db OOh,01h,45h,46h,endc
db 01h,05h,16h,36h,45h,41h,30h,10h,01h,endc
db 04h,26h,20h,endv,OOh,040h,endc
db 05h,16h,36h,45h,44h,OOh,40h,041h,endc
db 05h,16h,36h,45h,44h,33h,42h,41h,30h,10h,01h,endv
db 13h,033h,endc
db 06h,03h,043h,endv,20h,026h,endc
db 01h,10h,30h,41h,42h,33h,03h,06h,046h,endc
db 02h, 13h,33h,42h,41h,30h, 10h,01h,05h, 16h,36h,045h
db endc
db 06h,46h,44h,OOh,endc
db 01h,02h,13h,04h,05h,16h,36h,45h,44h,33h,42h,41h
db 30h,10h,01h,endv,13h,023h,endc
db 01h,10h,30h,41h,45h,36h,16h,05h,04h,13h,33h,044h
db endc
db 15h,25h,24h,14h,15h,endv,12h,22h,21h,11h,12h
db endc
db 15h,25h,24h,14h,15h,endv,21h,11h,12h,22h,20h,1fh
db endc
db 30h,03h,036h,endc
db 02h,042h,endv,04h,044h,endc
db 10h,43h,16h,endc
db 06h,17h,37h,46h,45h,34h,24h,022h,endv,21h,020h
db endc
db 50h,10h,01h,06h,17h,57h,66h,63h,52h,32h,23h,24h
db 35h,55h,064h,endc
db OOh,04h,26h,44h,040h,endv,03h,043h,endc
db OOh,06h,36h,45h,44h,33h,42h,41h,30h,OOh,endv
db 03h,033h,endc

Text Write Operations

font_43
font_44
font_45
fonL46
fonL47
fonL48
font_49
font_4a
font_4b
font_4c
font_4d
font_4e
font_4f
font_50
font_51
font_52
fonL53
fonL54
font_55
font_56
font_57
fonL58
fonL59
font_Sa
fonL5b
font_5c
font_5d
font_5e
fonL5f
font_60
fonL61
fonL62
font_63
font_64
fonL65
fonL66
fonL67

db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

45h,36h,16h,05h,01h,10h,30h,041h,endc
OOh,06h,36h,45h,41h,30h,OOh,endc
40h,OOh,06h,046h,endv,03h,023h,endc
OOh,06h,046h,endv,03h,023h,endc
45h,36h,16h,05h,01h,10h,30h,41h,43h,023h,endc
OOh,06h,endv,03h,043h,endv,40h,046h,endc
10h,030h,endv,20h,026h,endv,16h,036h,endc
01h,10h,30h,41h,046h,endc
OOh,06h,endv,02h,046h,endv,13h,040h,endc
40h,OOh,06h,endc
OOh,06h,24h,46h,040h,endc
OOh,06h,endv,05h,041h,endv,40h,046h,endc
01h,05h,16h,36h,45h,41h,30h,10h,01h,endc
OOh,06h,36h,45h,44h,33h,03h,endc
12h,30h,10h,01h,05h,16h,36h,45h,41h,30h,endc
OOh,06h,36h,45h,44h,33h,03h,endv,13h,040h,endc
01h,10h,30h,41h,42h,33h,13h,04h,05h,16h,36h
045h,endc
06h,046h,endv,20h,026h,endc
06h,01h,10h,30h,41h,046h,endc
06h,02h,20h,42h,046h,endc
06h,OOh,22h,40h,046h,endc
OOh,01h,45h,046h,endv,40h,41h,05h,06h,endc
06h,24h,020h,endv,24h,46h,endc
06h,46h,45h,01h,OOh,40h,endc
37h,17h,1fh,3fh,endc
06h,05h,41h,40h,endc
17h,37h,3fh,2fh,endc
04h,26h,044h,endc
Ofh,07fh,endc
54h,36h,endc
40h,43h,34h,14h,03h,01h,10h,30h,041h,endc
06h,01h,10h,30h,41h,43h,34h,14h,03h,endc
41h,30h,10h,01h,03h,14h,34h,043h,endc
46h,41h,30h,10h,01h,03h,14h,34h,43h,endc
41h,30h,10h,01h,03h,14h,34h,43h,42h,02h,endc
20h,25h,36h,46h,55h,endv,03h,43h,endc
41h,30h,10h,01h,03h,14h,34h,43h,4fh,3eh,1eh
Ofh,endc

9-47

Text Write Operations

font_68
fonL69
font_6a
fonL6b
font_6c
font_6d
font_6e
fonL6f
fonL 70

db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db
db

fonL71
fonL 72
fonL 73
font_74
font_75
font_76
fonL 77
font_78
fonL79
font_7a
fonL 7b
font_7c
fonL 7d
font_7e
font_7f
scale
dseg

9-48

db
ends
end

OOh,06h,endv,03h,14h,34h,43h,40h,endc
20h,23h,endv,25h,26h,endc
46h,45h,endv,43h,4fh,3eh,1eh,Ofh,endc
OOh,06h,endv,01h,34h,endv,12h,30h,endc
20h,26h,endc
OOh,04h,endv,03h,14h,23h,34h,43h,40h,endc
OOh,04h,endv,03h,14h,34h,43h,40h,endc
01h,03h,14h,34h,43h,41h,30h,10h,01h,endc
04h,Oeh,endv,01h,10h,30h,41h,43h,34h,14h
03h,endc
41h,30h,10h,01h,03h,14h,34h,43h,endv,44h
4eh,endc
00h,04h,endv,03h,14h,34h,endc
01h, 10h,30h,41h,32h, 12h,03h, 14h,34h
43h,endc
04h,44h,endv,26h,21h,30h,40h,51h,endc
04h,01h,10h,30h,41h,endv,44h,40h,endc
04h,02h,20h,42h,44h,endc
04h,OOh,22h,40h,44h,endc
00h,44h,endv,04h,40h,endc
04h,01h,10h,30h,41h,endv,44h,4fh,3eh,1eh
Ofh,endc
04h,44h,OOh,40h,endc
40h,11h,32h,03h,34h,15h,46h,endc
20h,23h,endv,25h,27h,endc
OOh,31h,12h,43h,14h,35h,06h,endc
06h,27h,46h,67h,endc
07,77,endc

10
Read Operations

The Read Process
Programming a read operation is simpler than programming a write operation. From the Graphics
Option's point of view, only the Mode and ALUjPS registers need to be programmed. There is no
need to involve the Foreground/Background Register, Text Mask, Write Buffer, or the Pattern
Generator. GDC reads are programmed much like text writes except for the action command which
in this case is RDAT. When reading data from the bitmap, only one plane can be active at anyone
time. Therefore, it can take four times as long to read back data as it did to write it in the first
place.

Read the Entire Bitmap
In the following example, the entire bitmap, one plane at a time, is read and written into a 64K byte
buffer in memory. This example compliments the example of displaying data from memory found in
Chapter 7.

10-1

Read Operations

Example of Reading the Entire Bitmap
.********************************************************************
,

*
pro c e d u r e

red v i d

this routine will read out all of display
memory, one plane at a time, then store
that data in a 64k buffer in motherboard
memory.

purpose:

entry:
exit:
register usage: ax,cx,di

*
*

*
*
*

*
*
*
*

.********************************************************************
,

dseg
segment byte
public 'datasg'
extrn
num_planes:byte,gbmod:byte,nmredl:word,gtemp:word,curlO:word
dseg ends
'vseg'
vidseg segment byte
public
public viddata
viddata db
Offffh dup ( ? )
vidseg ends
cseg segment byte public 'codesg'
extrn
gdc_not_busy:near,alups:near,fgbg:near,init_option:near
extrn
mode:near
assume cs:cseg,ds:dseg,es:dseg,ss:nothing
public redvid
redvid

proc

near

;Set up to enable reads.
The Graphics Option has to disable writes
;in the ALU/PS, enable a plane to be read in the Mode Register, and
;program the GDC to perform one plane's worth of reads.
;GDC programming consists of issuing a CURSOR command of 0, a mask
;of FFFFh, a FIGS command with a direction to the right and a read
;of an entire plane, and finally the RDAT command to start the read
;in motion.
Note that the GDC can't read in all 8000h words of a
;high resolution plane but it doesn't matter because not all 8000h
;words of a high resolution plane have useful information in them.

10-2

Read Operations

rd1:

c1d
call
mov
out
mov
out
mov
test
jnz
mov
mov

jclear the direction flag
gdc_not_busy
jmake sure the GDC is not busy
al,Oefh
53h,al
al,Ofh
jdisable all writes
51h,al
ax,3fffh
jassume high resolution read
byte ptr gbmod,01 jactually high resolution?
rd1
j jump if yes
ax,2000h
jmedium resolution no. of reads
word ptr nmredl,ax

jBlank the screen. This will let the GDC have 100% use of the time
jto read the screen in.
mov
out

al,Och
57h,al

jblank command

jSet up to transfer data as it is being read from the screen into
jthe VIDSEG data segment.

rd2:

mov
mov
mov
mov
xor
mov
mov
out
mov
sub
shl
shl
mov
and
or
out
mov
out
xor
out
out
mov
out
mov
out
out

jset up the es register to point
ax,vidseg
to the video buffer
eS,ax
di,O
jstart at beginning of the buffer
c1,byte ptr num_planes jinit routine sets this byte
jnum_planes = 2 or 4
ch,ch
jsave plane count
word ptr gtemp,cx
al,Obfh
jaddress the mode register
53h,al
al,byte ptr num_planes jfigure which plane to enable
al,cl
jshift to enable bits over 2
al,1
al,1
ah,byte ptr gbmod
jmode byte = no graphics,
plane to read, write enable
ah,Oe1h
jcombine with plane to read
al,ah
jassert new mode
51h,al
jposition the GDC cursor to
al,49h
57h,al
top left
al,al
56h,al
56h,al
jset all bits in GDC mask
al,4ah
57h,al
al,Offh
56h,al
56h,al

10-3

Read Operations

rd4:

mov
out
mov
out
mov
out
mov
out
mov
out
mov
shl
in
test
j z

in
stosb
loop

al,4ch
57h,al
al,2
56h,al
ax,word ptr nmredl
56h,al
al,ah
56h,al
al,OaOh
57h,al
cx,word ptr nmredl
cx,1
al,56h
al,1
rd4
al,57h

jassert the FIGS command
jdirection is to the right
jnumber of word reads to do

jstart the read operation now
jread in as they are ready.
jbytes = 2 * words read
ibyte ready to be read?
i jump i f not
iread the byte
istore in vid5eg

rd4

iWe've finished reading all of the information out of that plane.
ilf high resolution, increment di by a word because we were one
iword short of the entire 32k high resolution plane.
Recover the
iplane to read count and loop if not done.

rd5:

test
j z
stosw
mov
loop

byte ptr gbmod,1
rd5
idummy stos
cx,word ptr gtemp
rd2

ihigh resolution?
i jump if not
to keep no. reads=words/plane
iloop if more planes to be read

iWe're done with the read.
iRestore video refresh and set the high/medium re50lution flag byte
iat the end of vid5eg 50 that when it i5 written back into the video
iwe do it in the proper resolution.

rd6:
rd7:

redvid
c5eg

10-4

mov
out
te5t
jnz
xor
jmp
mov
mov
mov
mov
mov
ret
endp
end5
end

al,Odh
iunblank the 5creen
57h,al
byte ptr gbmod,1
ihigh re5?
rd6
ijump if ye5
al,al
ila5t byte
0 for medium re50lution
rd7
al,Offh
ila5t byte = ff for high re50lution
di,Offffh
i5et the re50lution flag
byte ptr e5:[dil,al
ax,d5eg
e5,ax
ire5tore e5

Read Operations

Pixel Write After a Read Operation
After a read operation has completed, the graphics option is temporarily unable to do a pixel write.
(Word writes are not affected by preceding read operations.) However, the execution of a word write
operation restores the option's ability to do pixel writes. Therefore, whenever you intend to do a
pixel write after a read operation, you must first execute a word write. This will ensure that
subsequent vectors, arcs, and pixels will be enabled.
The following code sequence will execute a word write operation that will not write anything into the
bitmap. The code assumes that the CDC is not busy since it has just completed a read operation. It
also assumes that this code is entered after all the required bytes have been read out of the FIFO
buffer.
,.********************************************************************
*
pro c e d u r e
*
*
purpose:

Execute a no-op word write after read operation is
completed.

*
*

*
,.********************************************************************
cseg
extrn

segment byte
public
'codesg'
imode:near,alups:near
public write_after_read
assume cs:cseg,ds:dseg,es:nothing,ss:nothing

mov
out

xor
call
mov
out
out
or
call
mov
out
xor
out
out
out

near
proc
;sometimes the GDC will not accept the
first command after a read - this command
can safely be missed and serves to ensure
that the FIFO buffer is cleared and
pointing in the right direction
b 1, b 1
;restore write enable replace mode to all
planes in the ALU/PS Register
alups
al,Offh ;disable writes to all bits at the
55h,al
option's Mask Registers
54h,al
byte ptr gbmod,10h ;enable writes to Mode Register
imode
;it is already in word mode
al,4ch
;unnecessary to assert cursor or mask since
57h,al
it doesn't matter where you write - the
al,al
write is completely disabled anyway 56h,al
just going through the word write
56h,al
operation will enable subseguent pixel
56h,al
writes
al,Odh
57h,al

10-5

Read Operations

mov
out
ret

al,22h
57h,al

jexecute the write operation
endp

c5eg
d5eg
extrn
d5eg

10-6

end5
5egment byte
gbmod:byte
end5
end

public

'data5g'

11
Scroll Operations

Vertical Scrolling
The Scroll map controls the lo~ation of 64-word blocks of display memory on the video monitor. In
medium resolution mode, this is two scan lines. In high resolution mode, this is one scan line. By
redefining scan line locations in the Scroll Map, you effectively move 64 words of data into new
screen locations.
All Scroll Map operations by the CPU start at location zero and increment by one with each succeeding CPU access. The CPU has no direct control over which Scroll Map location it is reading or
writing. All input addresses are generated by an eight-bit index counter which is cleared to zero
when the CPU first accesses the Scroll Map through the Indirect Register. There is no random
access of a Scroll Map address.
Programming the Scroll Map involves a number of steps. First ensure that the GDC is not currently
accessing the Scroll Map and that it won't be for some time (the beginning of a vertical retrace for
example). Clearing bit 5 of the Mode Register to zero enables the Scroll Map for writing. Clearing
bit 7 of the Indirect Register to zero selects the Scroll Map and clears the Scroll Map Counter to
zero. Data can then be entered into the Scroll Map by writing to port 5Ih. When the programming
operation is complete or just before the end of the vertical retrace period (whichever comes first)
control of the Scroll Map addressing is returned to the GDC by setting bit 5 of the Mode Register to
one.

11-1

Scroll Operations

If, for some reason, programming the Scroll Map requires more than one vertical retrace period,
there is a way to break the operation up into two segments. A read of the Scroll Map increments the
Scroll Map Index Counter just as though it were a write. You can therefore program the first half,
wait for the next vertical retrace, read the first half and then finish the write of the last half.

Example of Vertical Scrolling One Scan Line
,.********************************************************************
pro c e d u r e

c r

*
*
*

purpose:

move the current entire screen up one scan line *

entry:
exit:
register usage: ax,cx,di,si

*
*
*
*

,.********************************************************************
dseg
extrn
dseg
cseg
extrn
assume
public

segment byte public 'datasg'
scrltb:byte,gtemp1:byte,startl:byte,gbmod:byte isee Example 3
ends
segment byte public 'codesg'
ascrol:near
idefined in Example 3.
cs:cseg,ds:dseg,es:dseg,ss:nothing
vscroll

near
vscroll proc
iThe scrollmap controls which 64 word display memory segment will be
idisplayed on a particular screen line. The scroll map will display
ion the top high resolution scan line the 64-word segment denoted by
ithe data loaded into location 0.
If the data is a 0, the first
i64-word segment is accessed.
If the data is a 10, the 11th 64-word
isegment is displayed. By simply rewriting the order of 64-word
isegments in the scroll map, the order in which they are displayed is
icorrespondingly altered.
If the entire screen is to be scrolled up
ione line, the entire scroll map's contents are moved up one location.
iOata at address 1 is moved into address 0, data at address 2 is moved
iinto address 1 and so on.
A split screen scroll can be accomplished
iby keeping the stationary part of the screen unchanged in the scroll
imap while loading the appropriate information into the moving window.
iIf more than one scroll map location is loaded with the same data,
ithe corresponding scan will be displayed multiple times on the screen.

11-2

Scroll Operations

jNote that the information in the bitmap hasn't been changed, only the
jlocation where the information is displayed on the video monitor has
jbeen changed.
When the lines that used to be off the bottom of the
jscreen scroll up and become visible, they will have in them whatever
jhad been written there before.
If a guaranteed clear scan line is
jdesirable, the off-screen lines should be cleared with a write before
jthe scroll takes place.
jIn medium resolution, only the first 128 scroll map entries have
jmeaning because while each medium resolution scan is 32 words long,
jeach scroll map entry controls the location of 64 words of data.
In
jmedium resolution, this is the same as two entire scans. The scroll
jmap acts as if the most significant bit of the scroll map entries was
jalways O.
Loading an 80h into a location is the same as loading a O.
jLoading an 81h is the equivalent to writing a 1. The example shown
jbelow assumes a high resolution, 256 location, scrollmap.
Had it
jbeen medium resolution, only the first 128 scans would have been
jmoved. The other 128 scroll map locations still exist but are of no
jpractical use to the programmer. What this means to the applications
jprogrammer is that in medium resolution, after the scroll map has
jbeen initialized, the first 128 entries are treated as if they were
jthe only scroll map locations in the table.
j5ave the contents of the first section of the scroll table to be
joverwritten, fetch the data from however many scans away we want to
jscroll by, then move the contents of the table in a circular fashion.
jThe last entry to be written is the scan we first saved.
After the
jshadow scroll table has been updated, it can then be asserted by a
jcall to the "ascrol" routine in the "init_option" procedure.
mov
mov
lodsb
mov
mov
rep
mov
stosb
call
ret
vscroll endp
cseg
ends
end

si,offset scrltb
di,si
byte ptr gtemp1,al
cx,255
movsw
al,byte ptr gtemp1
ascrol

jset the source of the data
jset the destination of the data
jfetch the first scan
and save it
jmove the other 255 scroll
table bytes
jrecover the first scan and put
it into scan 256 location
jassert updated scroll table
to scroll map

11-3

Scroll Operations

Horizontal Scrolling
Not only can the video display be scrolled up and down but it can also be scrolled from side to side
as well. The GDC can be programmed to start video action at an address other than location 0000.
Using the PRAM command to specify the starting address of the display partition as 0002 will
effectively shift the screen two words to the left. Since the screen display width is not the same as
the number of words displayed on the line there is a section of memory that is unrefreshed. The
data that scrolls off the screen leaves the refresh area and it will also be unrefreshed. To have the
data rotate or wrap around the screen and be saved requires that data be read from the side about
to go off the screen and be written to the side coming on to the screen. If the application is not
rotating but simply moving old data out to make room for new information, the old image can be
allowed to disappear into the unrefreshed area.
Although the specifications for the dynamic RAMs only guarantee a data persistence of two milliseconds, most of the chips will hold data much longer. Therefore, it is possible to completely rotate
video memory off one side and back onto the other. However, applications considering using this
characteristic should be aware of the time dependency and plan accordingly.

Example of Horizontal Scrolling One Word
,.********************************************************************
pro c e d u r e
purpo5e:

1 1

move the current entire 5creen to right
or left a word addre55.

*
*
*
*

*
*

entry:

if al
O( move 5creen to the left.
if al (> 0, move 5creen to the right.

exit:
regi5ter u5age: ax

*
*
*

.********************************************************************
,

jThe GOC i5 programmable (on a word boundary> a5 to where it 5tart5
jdi5playing the 5creen. By incrementing or decrementing that 5tarting
jaddre55 word we can redefine the 5tarting addre55 of each 5can line
jand thereby give the appearance of horizontal 5crolling. A55ume that
jthi5 5tart window di5play addre55 i5 5tored in the variable5: 5tartl
jand 5tarth. Let'5 further a55ume that we want to limit 5crolling to
jone 5can line'5 worth. Therefore, in high re50lution we can never
ji55Ue a 5tarting addre55 higher than 63j in medium re50lution, none
jhigher than 31.

11-4

Scroll Operations

dseg
extrn
dseg
cseg
extrn
assume

segment byte publiC 'datasg'
scrltb:byte,gtemp1:byte,startl:byte,gbmod:byte
ends
segment byte public 'codesg'
gdc_not_busy:near
cs:cseg,ds:dseg,es:dseg,ss:nothing
public hscroll

hscroll proc
or
jz
dec
jmp
inc
test
jnz
and
jmp
and
hs3:

near
al,al
hs1
byte ptr
hs2
byte ptr
byte ptr
hs3
byte ptr
hs4
byte ptr

start!
start!
gbmod,1
startl,31
startl,63

;move screen to left?
; jump if not
;move screen to right
;move screen to left
;high res?
; jump if yes
;limit to 1s t medium
resolution scan
;limit to 1 s t high
resolution scan

;Assert the new startl, starth to the GDC.
Assume that starth is
;always going to be 0 although this is not a necessity. Issue the
;PRAM command and rewrite the starting address of the GDC display
;window O.
call
mov
out
mov
out
xor
out
ret
hscroll endp
ends
cseg
end

gdc_not_busy
al,70h
57h,al
al,byte ptr startl
56h,al
al,al
56h,al

;make sure the GDC is not busy
;issue the PRAM command
;fetch low byte of the starting
address
;assume high byte is always 0

11-5

12
Programming Notes

Shadow Areas
Most of the registers in the Graphics Option control more than one function. In addition, the registers are write-only areas. In order to change selected bits in a register while retaining the settings of
the rest, shadow images of these registers should be kept in motherboard memory. The current
contents of the registers can be determined from the shadow area, selected bits can be set or reset
by ORing or ANDing into the shadow area, and the result can be written over the existing register.
Modifying the Color Map and the Scroll Map is also made easier using a shadow area in motherboard
memory. These are relatively large areas and must be loaded during the time that the screen is
inactive. It is more efficient to modify a shadow area in motherboard memory and then use a fast
move routine to load the shadow area into the Map during some period of screen inactivity such as a
vertical retrace.

Bitmap Refresh
The Graphics Option uses the same memory accesses that fill the screen with data to also refresh
the memory. This means that if the screen display stops, the dynamic video memory will lose all the
data that was being displayed within two milliseconds. In high resolution, it takes two scan lines to
refresh the memory (approximately 125 microseconds). In medium resolution, it takes four scan lines
to refresh the memory (approximately 250 microseconds). During vertical retrace (1.6 milliseconds)
and horizontal retrace (10 microseconds) there is no refreshing of the memory. Under a worst case
condition, you can stop the display for no more than two milliseconds minus four medium resolution
scans minus vertical retrace or just about 150 microseconds. This is particularly important when
programming the Scroll Map.

12-1

Programming Notes

All write and read operations should take place during retrace time. Failure to limit reads and writes
to retrace time will result in interference with the systematic refreshing of the dynamic RAMs as
well as not displaying bitmap data during the read and write time. However, the GDC is usually
programmed to limit its bitmap accesses to retrace time as part of the initialization process.

Software Reset
Whenever you reset the GDC by issuing the RESET command (a write of zero to port 57h), the
Graphics Option must also be reset (a write of any data to port 50h). This is to synchronize the
memory operations of the Graphics Option with the read/modify/write operations generated by the
GDC. A reset of the Graphics Option by itself does not reset the GDC; they are separate reset
operations.

Setting Up Clock Interrupts
With the Graphics Option installed on a Rainbow system, there are two 60 hz clocks available to the
programmer-one from the motherboard and one from the Graphics Option. The motherboard clock
is primarily used for a number of system purposes. However, you can intercept it providing that any
routine that is inserted be kept short and compatible with the interrupt handler. Refer to the
"init_ option" procedure in Chapter 5 for a coding example of how to insert a new interrupt
vector under MS-DOS.
Clock interrupt types and vector addresses differ depending on the model of the motherboard as well
as whether the interrupt is for the Graphics Option or for the motherboard. (Refer to Table 3.)
It is important to keep all interrupt handlers short! Failure to do so can cause a system reset when

the motherboard's MHFU line goes active. New interrupt handlers should restore any registers that
are altered by the routine.
Table 3. Clock Interrupt Parameters

MOTHERBOARD
MODEL

INTERRUPT
TYPE

VECTOR
ADDRESS

GRAPHICS

22h

88h

OPTION

A2h

288h

20h

80h

AOh

280h

MOTHERBOARD

LJ-0229

12-2

Programming Notes

Operational Requirements
All data modifications to the bitmap are performed by hardware that is external to the GDC. In this
environment, it is a requirement that the GDC be kept in graphics mode and be programmed to
write in Replace mode. Also, the internal write data patterns of the GDC must be kept as all ones
for the external hardware to function correctly. The external hardware isolates the GDC from the
data in the bitmap such that the GDC is not aware of multiple planes or incoming data patterns.
Although it is possible to use the GDC's internal parameter RAM for soft character fonts and
graphics characters, it is faster to use the option's Write Buffer. However, to operate in the GDC's
native mode, the Write Buffer and Pattern Generator should be loaded with all ones, the Mode
Register should be set to graphics mode, and the Foreground/Background Register should be loaded
with FOh.
When the Graphics Option is in Word Mode, the GDC's mask register should be filled with all ones.
This causes the GDC to go on to the next word after each pixel operation is done. The external
hardware in the meantime, has taken care of all sixteen bits on all four planes while the GDC was
taking care of only one pixel.
When the option is in Vector Mode, the GDC is also in graphics mode. The GDC's mask register is
now set by the third byte of the cursor positioning command (CURS). The GDC will be able to tell
the option which pixel to perform the write on but the option sets the mode, data and planes.

Set-Up Mode
When you press the SET-UP key on the keyboard, the system is placed in set-up mode. This, in
turn, suspends any non-interrupt driven software and brings up a set-up screen if the monitor is
displaying VTI02 video output. If, however, the system is displaying graphics output, the fact that
the system is in set-up mode will not be apparent to a user except for the lack of any further
interaction with the graphics application that has been suspended. The set-up screen will not be
displayed.
Users of applications that involve graphics output should be warned of this condition and cautioned
not to press the SET-UP key when in graphics output mode. Note also that pressing the SET-UP
key a second time will resume the execution of the suspended graphics software.
In either case, whether the set-up screen is displayed or not, set-up mode accepts any and all
keyboard data until the SET-UP key is again pressed.

12-3

Programming Notes

Timing Considerations
It is possible for an application to modify the associated hardware that is external to the CDC
(registers, buffers, maps) before the CDC has completed all pending operations. If this should occur,
the pending operations would then be influenced by the new values with unwanted results.

Before changing the values in the registers, buffers, and color map, you must ensure that the CDC
has completed all pending operations. The "gdc_not_busy" subroutine in the "init_option"
procedure in Chapter 5 is one method of checking that the CDC has completed all pending
operations.

12-4

Contents

PART III
Chapter 13. Option Registers, Buffers, and Maps
I/O Ports 13-1
Indirect Register 13-3
Write Buffer 13-4
Write Mask Registers 13-5
Pattern Register 13-6
Pattern Multiplier 13-7
Foreground/Background Register
ALU/PS Register 13-9
Color Map 13- 10
Mode Register 13-11
Scroll Map 13- 12

13-1

13-8

Chapter 14. GDC Registers and Buffers

14-1

Status Register 14-1
FIFO Buffer 14-2

Chapter 15. GDC Commands

15-1

Introduction 15-1
Video Control Commands 15-2
CCHAR - Specify Cursor and Character Characteristics
RESET - Reset tt)e GDC 15-3
SYNC - Sync Format Specify 15-6
VSYNC - Vertical Sync Mode 15-8

15-2

Contents
\

Display Control Commands 15-8
BCTRL - Control Display Blanking 15-8
CURS - Specify Cursor Position 15-9
PITCH - Specify Horizontal Pitch 15-10
PRAM - Load the Parameter RAM 15-10
START - Start Display and End Idle Mode 15-12
ZOOM - Specify the Zoom Factor 15-12
Drawing Control Commands 15-13
FIGD - Start Figure Drawing 15-13
FIGS - Specify Figure Drawing Parameters 15-14
GCHRD - Start Graphics Character Draw and Area Fill
MASK - Load the Mask Register 15-16
WDA T - Write Data into Display Memory 15-17
DATA READ COMMANDS 15-1 8
RDA T - Read Data from Display Memory 15-18

15-16

13
Option Registers, Buffers, and
Maps

The Graphics Option uses a number of registers, buffers, and maps to generate graphic images and
control the display of these images on a monochrome or color monitor. Detailed discussions of these
areas may be found in Chapter 3 of this manual.

I/O Ports
The CPUs on the Rainbow system's motherboard use the following I/O ports to communicate with
the Graphics Option:
Port

Function

50h

Graphics option software reset and resynchronization.

51h

Data input to area selected through port 53h.

52h

Data input to the Write Buffer.

13-1

Option Registers, Buffers, and Maps

53h

Area select input to Indirect Register.

54h
55h
56h

Input to low-order byte of Write Mask.

57h

Command input to GDC - Data output from GDC.

13-2

Input to high-order byte of Write Mask.
Parameter input to GDC - Status output from GDC.

Option Registers, Buffers, and Maps

Indirect Register
The Indirect Register is used to select one of eight areas to be written into.
Write data byte to port 53h.

Load Data:

INDIRECT REGISTER

o
LJ-0230

where:
Data
Byte

Active
Bit

Function

FEh

selects the Write Buffer

FDh

selects the Pattern Multiplier. (Pattern Multiplier must always be loaded before the Pattern Register)

FBh

selects the Pattern Register.

F7h

selects the Foreground/Background Register.

EFh

selects the ALUjPS Register.

DFh

selects the Color Map and resets the Color Map Address Counter to
zero.

"BFh

selects the Graphics Option Mode Register.

7Fh

selects the Scroll Map and resets the Scroll Map Address Counter to
zero.

NOTE
If more than one bit is set to zero, more than one area will be selected and
the results of subsequent write operations will be unpredictable.

13-3

Option Registers, Buffers, and Maps

Write Buffer
The Write Buffer is the incoming data source when the Graphics Option is in Word Mode.
Select Area:

write FEh to port 53h

Clear Counter:

write any value to port 51h

Load Data:

write up to 16 bytes to port 52h
AS THE GDC ACCESSES IT

AS THE CPU ACCESSES IT
(16 X 8-BIT RING BUFFER)

BYTE

7
0,1

~--------~

WORD

r---------~

(8 X 1 6-BIT WORDS)

2,3
4,5

6.7

8,9

10,11

12,13

14,15

7
LJ-0231

13-4

Option Registers, Buffers, and Maps

Write Mask Registers
The Write Mask Registers control the writing of individual bits in a bitmap word.
Select Area:

no selection required

Load Data:

write low-order data byte to port 54h
write high-order data byte to port 55h
AS ACCESSED BY
THE CPU

PaRr 55h

PaRr 54h

7---------07---------0
WRITE MASK (HIGH)

WRITE MASK (LOW)

15,--------------------0

LJ-0232

AS ACCESSED BY THE GDC

where:
bit = 0

enables a write in the corresponding bit position of the word being
displayed.

bit = 1

disables a write in the corresponding bit position of the word being
displayed.

13-5

Option Registers, Buffers, and Maps

Pattern Register
The Pattern Register provides the incoming data when the Graphics Option is in Vector Mode.
Select Area:

write FBh to port 53h

Load Data:

write data byte to port 51h
7

:--~
I
I

0
BITMAP

PAT

I--~•• WRITE

ERN

CIRCUITRY

IL __________________________ .JI
LJ-0233

where:
Pattern

13-6

is the pixel data to be displayed by the option when in Vector Mode.

Option Registers, Buffers, and Maps

Pattern Multiplier
The Pattern Multiplier controls the recirculating frequency of the bits in the Pattern Register.
Select Area:

write FDh to port 53h

Load Data:

write data byte to port 51h
4

7
UNUSED

3
VALUE

LJ-0234

where:
value

is a number in the range of 0 through 15 such that 16 minus this value is the
factor that determines when the Pattern Register is shifted.

13-7

Option Registers,
Buffers, and Maps
. .
.
'"

Foreground/Background Register
The Foreground/Background Register controls the bit/plane input to the bitmap.
Select Area:

write F7h to port 53h

Load Data:

write data byte to port 51h
7
7

DATA BYTE

FOREGROUND
REGISTER

BACKGROUND
REGISTER
LJ0235

where:

Bits
0-3

are the bits written to bitmap planes 0-3 respectively when the option is in REPLACE mode and the incoming data bit is a zero.
If the option is in OVERLAY or COMPLEMENT mode and the incoming data bit is
a zero, there is no change to the bitmap value.

4-7

are the bits written to bitmap planes 4-7 respectively when the option is in REPLACE or OVERLAY mode and the incoming data bit is a one.
If the option is in COMPLEMENT mode and the incoming data bit is a one, the
Foreground bit determines the action. If it is a one, the bitmap value is inverted; if
it is a zero, the bitmap value is unchanged.

Option Registers, Buffers, and Maps

ALU IPS Register
The ALUjPS Register controls the logic used in writing to the bitmap and the inhibiting of writing to
specified planes.
Select Area:

write EFh to port 53h

Load Data:

write data byte to port 51h
7
7

DATA BYTE

ALU

UNUSED

2
PLANE SELECT

LJ-0236

where:

Bit

Value

Function

0
1

enable writes to plane 0
inhibit writes to plane 0

0
1

enable writes to plane
inhibit writes to plane 1

0
1

enable writes to plane 2
inhibit writes to plane 2

0
1

enable writes to plane 3
inhibit writes to plane 3

5,4

place option in REPLACE mode

place option in COMPLEMENT mode

place option in OVERLAY mode

Unused

7,6

Unused

13-9

Option Registers, Buffers, and Maps

Color Map
The Color Map translates bitmap data into the monochrome and color intensities that are applied to
the video monitors.
Select Area:

write DFh to port 53h (also clears the index counter)

Coordinate:

wait for vertical sync interrupt

Load Data:

write 32 bytes to port 51h

2ND 16 BYTES
LOADED BY
THE CPU
MONO.
DATA

BLUE
DATA

1 ST 16 BYTES
LOADED BY
THE CPU
RED
DATA

GREEN
DATA

BYTE 17

BYTE 1

BYTE 18

BYTE 2

BYTE 19

BYTE 3

BYTE 20

BYTE 4

BYTE 21

BYTE 5

BYTE 22

BYTE 6

BYTE 23

BYTE 7

1
13-10

BYTE 32

BYTE 16

LJ-0237

Option Registers, Buffers, and Maps

Mode Register
The Mode Register controls a number of the Graphics Option's operating characteristics.
Select Area:

write BFh to port 53h

Load Data:

write data byte to port 51h

o
LJ-0238

where:

Bit

Value

Function

place option in medium resolution mode
place option in high resolution mode

o
1

place option into word mode
place option into vector mode

3,2

00
01
10
11

select plane 0 for readback operation
select plane 1 for readback operation
select plane 2 for read back operation
select plane 3 for readback operation

enable readback operation
enable write operation

1
5

o
1

enable writing to the Scroll Map
disable writing to the Scroll Map
disable vertical sync interrupts to CPU
enable vertical sync interrupts to CPU
disable video output from Graphics Option
enable video output from Graphics Option

NOTE
The Mode Register must be reloaded following any write to port 50h
(software reset).

13-11

Option Registers, Buffers, and Maps

Scroll Map
The Scroll Map controls the location of each line displayed on the monitor screen.
Preliminary:

enable Scroll Map writing (Mode Register bit 5 = 0)

Select Area:

write 7Fh to port 53h (also clears the index counter)

Coordinate:

wait for vertical sync interrupt

Load Data:

write 256 bytes to port 51h

Final:

disable Scroll Map writing (Mode Register bit 5 = 1)
256 X 8
RECIRCULATING
RING BUFFER

GDC

o
GDC LINE
ADDRESS
(BITS 6-13

XXXXXXXX

•
•
•
•
•

255

•
•

BITMAP LINE
ADDRESS
(BITS 6-13)
L--_ _ _ _ _ _ _ _ _ _

BIT MAP
LJ0239

where:

13-12

GDC Line
Address

is the line address as generated by the GDC and used as an index into
the Scroll Map.

Bitmap Line
Address

is the offset line address found by indexing into the Scroll Map. It becomes the new line address of data going into the bitmap.

14
GDC Registers and Buffers
The GDC has an 8-bit Status Register and a 16 x 9-bit first-in, first-out (FIFO) Buffer that provide
the interface to the Graphics Option. The Status Register supplies information on the current activity
of the GDC and the status of the FIFO Buffer. The FIFO Buffer contains GDC commands and
parameters when the GDC is in write mode. It contains bitmap data when the GDC is in read mode.

Status Register
The GDC's internal status can be interrogated by doing a read from port 56h. The Status Register
contents are as follows:

I I I
4

oj
LJ0240

where:

Bit

Status

Explanation

DATA READY

When set, data is ready to be read from the FIFO.

FIFO FULL

When set, the command/parameter FIFO is full.

FIFO EMPTY

When set, the command/parameter FIFO is completely empty.

DRAWING IN
PROGRESS

When set, the GDC is performing a drawing function. Note,
however, that this bit can be cleared before the DRAW command is fully completed. The GDC does not draw continuously
and this bit is reset during interrupts to the write operation.

DMA EXECUTE

Not used.

VERTICAL SYNC
ACTIVE

When set, the GDC is doing a vertical sync.

HORIZONTAL
SYNC ACTIVE

When set, the GDC is doing a horizontal sync.

LIGHT PEN DETECTED

Not used.

GDC Registers and Buffers

FrfO Buffer
You can both read from and write to the FIFO Buffer. The direction that the data takes through the
buffer is controlled by the Rainbow system using CDC commands. CDC commands and their associated parameters are written to ports 57h and 56h respectively. The CDC stores both in the FIFO
Buffer where they are picked up by the CDC command processor. The CDC uses the ninth bit in the
FIFO Buffer as a flag bit to allow the command processor to distinguish between commands and
parameters. Contents of the bitmap are read from the FIFO using reads from port 57h.
DATA BYTE

FLG
8

o
COMMANDS AND
PARAMETERS
FROM THE CPU _

DATA FROM
.tI---THE BITMAP

3
BITMAP DATA_
TO THE CPU

COMMANDS AND
PARAMETERS TO
THE COMMAND
PROCESSOR

... v

where:
flg

is a flag bit to be interpreted as:

o - data byte is a parameter
1 - data byte is a command
data byte

is a CDC command or parameter

When you reverse the direction of flow in the FIFO Buffer, any pending data in the FIFO is lost. If a
read operation is in progress and a command is written to port 56h, the unread data still in the FIFO
is lost. If a write operation is in progress and a read command is processed, any unprocessed
commands and parameters in the FIFO Buffer are lost.

14-2

15
GDC COMMANDS

Introduction
This chapter contains detailed reference information on the GDC commands and parameters supported by the Graphics Option. The commands are listed in alphabetical order within functional
category as follows:
•

Video Control Commands
CCHAR
RESET
SYNC
VSYNC

•

Specifies the cursor and character row heights
Resets the GDC to its idle state
Specifies the video display format
Selects Master/Slave video synchronization mode

Display Control Commands
BCTRL
CURS
PITCH
PRAM
START
ZOOM

Controls the blanking/unblanking of the display
Sets the position of the cursor in display memory
Specifies the width of display memory
Defines the display area parameters
Ends idle mode and unblanks the display
Specifies zoom factor for the graphics display

15-1

GDC Commands

• Drawing Control Commands
FIGD
FIGS
GCHRD
MASK
WDAT
•

Data Read Commands
RDAT

15-2

Draws the figure as specified by FIGS command
Specifies the drawing controller parameters
Draws the graphics character into display memory
Sets the mask register contents
Writes data words or bytes into display memory

Reads data words or bytes from display memory

GDC Commands

Video Control Commands
CCHAR - Specify Cursor and Character Characteristics
Use the CCHAR command to specify the cursor and character row heights and characteristics.
COMMAND BYTE

PARAMETER BYTES

BR(LO)

CTOP

CBOT

BR(HI)
LJ-0242

where:
DC

controls the display of the cursor

o - do not display cursor
1 - display the cursor
LR

is the number of lines per character row, minus 1

is the blink rate (5 bits)

controls the action of the cursor

o - blinking cursor
1 - steady cursor
CTOP

is the cursor's top line number in the row

CBOT

is the cursor's bottom line number in the row
(CBOT must be less than LR)

15-3

GDC Commands

RESET - Reset the GDC
Use the RESET command to reset the GDC. This command blanks the display, places the GDC in
idle mode, and initializes the FIFO buffer, command processor, and the internal counters. If parameter bytes are present, they are loaded into the sync generator.
COMMAND BYTE

PARAMETER BYTES

VS(LO)

HFP

VS(HI)

HBP

VFP

AL(LO)

VBP

AL(HI)

LJ-0243

15-4

GDC Commands

where:
CG

sets the display mode for the GDC
00 - mixed graphics and character mode
01 - graphics mode only
10 - character mode only
11 - invalid

controls the video framing for the GDC
00 - noninterlaced
01 - invalid
10 - interlaced repeat field for character displays
11 - interlaced

controls the RAM refresh cycles

o - no refresh - static RAM
1 - refresh - dynamic RAM
F

controls the drawing time window

o - drawing during active display time and retrace blanking
1 - drawing only during retrace blanking
AW

active display words per line minus 2; must be an even number

horizontal sync width minus 1

vertical sync width

HFP

horizontal front porch width minus 1

HBP

horizontal back porch width minus 1

VFP

vertical front porch width

active display lines per video field

VBP

vertical back porch width

15-5

GDC Commands

SYNC - Sync Format Specify
Use the SYNC command to load parameters into the sync generator. The GDC is neither reset nor
placed in idle mode.
COMMAND BYTE

LJ-0244

where:
DE

controls the display

o - disables (blanks) the display
1 - enables the display
PARAMETER BYTES

VS(LO)

VS(HII

HFP

HBP

VFP

AL(LO)

VBP

AL(HI)
LJ-0244

15-6

GDC Commands

where:
CC

sets the display mode for the CDC
00 - mixed graphics and character mode
01 - graphics mode only
10 - character mode only
11 - invalid

controls the video framing for the CDC
00 - noninterlaced
01 - invalid
10 - interlaced repeat field for character displays
11 - interlaced

controls the RAM refresh cycles

o - no refresh - static RAM
1 - refresh - dynamic RAM
F

controls the drawing time window

o - drawing during active display time and retrace blanking
1 - drawing only during retrace blanking
AW

active display words per line minus 2; must be an even number

horizontal sync width minus 1

vertical sync width

HFP

horizontal front porch width minus 1

HBP

horizontal back porch width minus 1

VFP

vertical front porch width

active display lines per video field

VBP

vertical back porch width

15-7

GDC Commands

VSYNC - Vertical Sync Mode
Use, the VSYNC command to control the slave/master relationship whenever mUltiple GDC's are
used to contribute to a single image.
COMMAND BYTE
7

o
M
LJ-0245

where:
M

sets the synchronization status of the GDC

o - slave mode (accept external vertical sync pulses)
1 - master mode (generate and output vertical sync pulses)

15-8

GDC Commands .

Display Control Commands
BCTRL - Control Display Blanking
Use the BCTRL command to specify whether the display is blanked or enabled.
COMMAND BYTE
7

o
DE
LJ-0246

where:
DE

controls the display

o - disables (blanks) the display
1 - enables the display

15-9

GDC Commands

CURS - Specify Cursor Position
Use the CURS command to set the position of the cursor in display memory. In character mode the
cursor is displayed for the length of the word. In graphics mode the word address specifies the word
that contains the starting pixel of the drawing; the dot address specifies the pixel within that word.
COMMAND BYTE

I°I°

PARAMETER BYTES

EAD(LO}

EAD(MID}

'--_ _ _ _
dA_D
_ _ _ _......._O_.l--_O_.l--_E_A_D_(H_I_}---,r-GRAPHICS MODE ONLY
LJ-0213

where:

15-10

EAD

is the execute word address (18 bits)

dAD

is the dot address within the word

GDC Commands

PITCH - Specify Horizontal Pitch
Use the PITCH command to set the width of the display memory. The drawing processor uses this
value to locate the word directly above or below the current word. It is also used during display to
find the start of the next line.
COMMAND BYTE

I I
a

PARAMETER BYTES

7
P1

P
LJ-0214

where:
P

is the number of word addresses in display memory in the horizontal direction

15-11

GDC Commands

PRAM - Load the Parameter RAM
Use the PRAM command to load up to 16 bytes of information into the parameter RAM at specified
adjacent locations. There is no count of the number of parameter bytes to be loaded; the sensing of
the next command byte stops the load operation. Because the Graphics Option requires that the GDC
be kept in graphics mode, only parameter bytes one through four, nine, and ten are used.
COMMAND BYTE
7

2
SA

LJ-0247

where:
SA

15-12

is the start address for the load operation (Pn - 1)

GDC Commands

PARAMETER BYTES

SAD(LO)

SAD(MID)

LEN(LO)

SAD(HI)

LEN(HI)

UNUSED

•
•
•
P8

UNUSED

Pl0

UNUSED

Pll

•
P·l

L.._ _ _ _ _ _ _ _ _
U_N_U_SE_D_ _ _ _ _ _ _ _--.I

LJ-0247

where:
SAD

is the start address of the display area (18 bits)

LEN

is the number of lines in the display area (10 bits)

15-13

GDC Commands

sets the display width

o - one word per memory cycle (16 bits)
1 - two words per memory cycle (8 bits)
1M

sets the current type of display when the CDC is in mixed graphics and character
mode

o - character area
1 - image or graphics area

NOTE
When the CDC is in graphics mode, the 1M bit must be a zero.

15-14

GDC Commands

START - Start Display and End Idle Mode
Use the START command to end idle mode and enable the video display,
COMMAND BYTE
7

LJ-0248

15-15

GDC Commands

ZOOM - Specify the Zoom Factor
Use the ZOOM command to set up a magnification factor of 1 through 16 (using codes 0 through
15) for the display and for graphics character writing.
COMMAND BYTE

PARAMETER BYTES

7
P1

6
DISP

2
GCHR

LJ-0249

where:

15-16

DISP

is the zoom factor (minus one) for the display

GCHR

is the zoom factor (minus one) for graphics character writing and area fills

GDC Commands

Drawing Control Commands
FIGD - Start Figure Drawing
Use the FIGD command to start drawing the figure specified with the FIGS command. This command causes the GDC to:
• load the parameters from the parameter RAM into the drawing controller, and
• start the drawing process at the pixel pointed to by the cursor: Execute Word Address (EAD)
and Dot Address within the word (dAD)
COMMAND BYTE
7
0

4
0

2
0

0
LJ-0250

15-17

GDC Commands

FIGS - Specify Figure Drawing Parameters
Use the FIGS command to supply the drawing controller with the necessary figure type, direction,
and drawing parameters needed to draw figures into display memory.
COMMAND BYTE

PARAMETER BYTES

D2(LO)

P11

D2(HI)

D1 (LO)

D1 (HI)

DM(LO)

P10

D(HI)

DC(HI)

D(LO)

DIR

DC(LO)

DM(HI)
LJ·0251

15-18

GDC Commands

where:
SL

Slanted Graphics Character

Rectangle

Figure Type Select Bits

Arc/Circle

Graphics Character

(see valid
combinations
below)

Line (Vector)

DIR

is the drawing direction base (see definitions below)

is the DC drawing parameter (14 bits)

is the graphic drawing flag used in mixed graphics and character mode

is the D drawing parameter (14 bits)

is the D2 drawing parameter (14 bits)

is the D1 drawing parameter (14 bits)

is the DM drawing parameter (14 bits)
FIGURE TYPE SELECT BITS (VALID COMBINATIONS)

SL R A GC L

OPERATION

o0 0 0 0

CHARACTER DISPLAY MODE DRAWING, INDIVIDUAL DOT
DRAWING, WDAT, AND RDAT

00001

STRAIGHT LINE DRAWING

00010

GRAPHICS CHARACTER DRAWING AND AREA FILL WITH
GRAPHICS CHARACTER PATTERN

o0 10 0

ARC AND CIRCLE DRAWING

o 1 000

RECTANGLE DRAWING

10010

SLANTED GRAPHICS CHARACTER DRAWING dfJD SLANTED
AREA FILL

15-19

GDC Commands

DRAWING DIRECTION BASE (DIR)
[101)

[100)

[011)

"'t/

[110)..-- [START) ~ [010)

[111)

/!~
[000)

[001)
LJ-0252

15-20

GDC Commands

GCHRD - Start Graphics Character Draw and Area Fill
Use the GCHRD command to initiate the drawing of the graphics character or area fill pattern that
is stored in the Parameter RAM. The drawing is further controlled by the parameters loaded by the
FIGS command. Drawing begins at the address in display memory pointed to by the Execute Address
(EAD) and Dot Address (dAD) values.
COMMAND BYTE
7

o
LJ-0253

15-21

GDC Commands

MASK - Load the Mask Register
Use the MASK command to set the value of the 16-bit Mask Register that controls which bits of a
word can be modified during a Read/Modify/Write (RMW) cycle.
COMMAND BYTE

I I
0

PARAMETER BYTES

M(LO)

M(HI)

LJ-0254

where:
M

is the bit configuration to be loaded into the Mask Register (16 bits). Each bit in
the Mask Registercontrols the writing of the corresponding bit in the word being
processed as follows:

o - disable writing
1 - enable writing

15-22

GDC Commands

WDAT - Write Data Into Display Memory
Use the WDAT command to perform RMW cycles into display memory starting at the location
pointed to by the cursor Execute Word Address (EAD). Precede this command with a FIGS command to supply the writing direction (DIR) and the number of transfers (DC).
COMMAND BYTE
7

TYPE

MOD
LJ-0255

where:
TYPE

is the type of transfer
00 - word transfer (first low then high byte)
01 - invalid
10 - byte transfer (low byte of the word only)
11 - byte transfer (high byte of the word only)

MOD

is the RMW memory logical operation
00 - REPLACE with Pattern
01 - COMPLEMENT
10 - RESET to Zero
11 - SET to One
PARAMETER BYTES
7

p11~_____________W_O_R_D_(_LO_)_O_R__BYT__E____________~

~2~1_______________W__O_R_D_(H_I)______________~
•

LJ-0255

where:
WORD

is a 16-bit data value

BYTE

is an 8-bit data value

15-23

GDC Commands

Data Read Commands
RDAT - Read Data From Display Memory
Use the RDAT command to read data from display memory and pass it through the FIFO buffer and
microprocessor interface to the host system. Use the CURS command to set the starting address
and the FIGS command to supply the direction (DIR) and the number of transfers(DC). The type of
transfer is coded in the command itself.
COMMAND BYTE

I I

3
TYPE

2
0

0
MOD
LJ-0256

where:
TYPE

is the type of transfer
00 - word transfer (first low then high byte)
01 - invalid
10 - byte transfer (low byte of the word only)
11 - byte transfer (high byte of the word only)

MOD

is the RMW memory logical operation
00 - REPLACE with Pattern
01 - COMPLEMENT
10 - RESET to Zero
11 - SET to One

NOTE
The MOD field should be set to 00 if no modification to the video buffer is
desired.

15-24

Contents

PART IV
Appendix A. Option Specification Summary

A-1

Physical Specifications A- 1
Environmental Specifications A- 1
Temperature A- 1
Humidity A-l
Altitude A-2
Power Requirements A-2
Standards and Regulations A-2
Part and Kit Numbers A-3

Appendix B. Rainbow Graphics Option _. Block Diagram
Appendix C. Getting Help

C-1

B-1

A
Option Specification Summary

Physical Specifications
The Graphics Option Video Subsystem is a 5.7" X 10.0", high density, four-layer PCB with one 40pin female connector located on side 1. This connector plugs into a shrouded male connector located
on the system module. The option module is also supported by two standoffs.

Environmental Specifications
Temperature
• Operating ambient temperature range is 10 to 40 degrees C.
• Storage temperature is -40 to 70 degrees C.

Humidity
•

10% to 90% non-condensing

•

Maximum wet bulb, 28 degrees C.

•

Minimum dew point, 2 degrees C.

A-l

Option Specification Summary

Altitude
• Derate maximum operating temperature 1 degree per 1,000 feet elevation
• Operating limit: 22.2 in. Hg. (8,000 ft.)
• Storage limit: 8.9 in Hg. (30,000 ft.)

Power Requirements
Calculated Typical

Calculated Maximum

+5V DC (+/-5%)

3.05 amps

3.36 amps

+12V DC (+/-10%)

180 rnA

220 rnA

Standards and Regulations
The Graphics Option module complies with the following standards and recommendations:
•

DEC Standard 119 - Digital Product Safety (covers UL 478, UL 114, CSA 22.2 No. 154, VDE
0806, and IEC 380)

• IEC 485 - Safety of Data Processing Equipment
•

EIA RS170 - Electrical Performance Standards - Monochrome Television Studio Facilities

• CCITT Recommendation V.24 - List of Definitions for Interchange Circuit Between Data Terminal Equipment and Data Circuit Terminating Equipment
• CCITT Recommendation V.28 - Electrical Characteristics for Unbalanced Double-Current
Interchange Circuits

A-2

Option Specification Summary

Part and Kit Numbers
Graphics Option

PC1XX-BA

Hardware:
Printed Circuit Board

54-15688

Color RGB Cable

BCC17-06

Software and Documentation:
Rainbow Color/Graphics Option Installation Guide

EK-PCCOL-IN-001

Rainbow Color/Graphics Option Programmer's Reference Guide

AA-AE36A-TV

Rainbow GSX-86 Programmer's Reference Manual

AA-V526A-TV

Rainbow GSX-86 Getting Started

AA-W964A-TV

Rainbow Diagnostic/GSX-86 Diskette

BL-W965A-RV

Rainbow 100 CP/M-86/80 V1.0 Technical Documentation

QV043-GZ

Rainbow 100 MS-DOS V2.01 Technical Documentation

QV025-GZ

A-3

B
Rainbow Graphics Option Block Diagram

8-1

PARAMETER
STATUS

COMMAND
(0 READBACK
DATA

GDC DATA

FIFO
(16 X 9)

/
/16

GDC ADDRESS BITS 0-5

GDC WRITE

PIXEL
MASK

GDC ADDRESS ~

BITS 6-13

SCROLL MAP
INDEX
COUNTER
(0-255)

PIXEL IN WORD
WRITE

@
1
PATTERN
A N D ) - MULTIPLIER
(0-15)

~
51

WRITE
8UFFER
(16 X 8)

PATTERN REGISTER

FOREGROUND/BACKGROUND REGISTER

ALU FUNCTION/PLANE SELECT REGISTER

COLOR/MONO MAP (INDEX COUNTER CLEAR)

MODE REGISTER

SCROLL MAP (INDEX COUNTER CLEAR)

II
!~

53/16
51/M2,M3

/
/

VIDEO OUTPUT
CIRCUITRY
(SHIFT REGISTER)

COLOR/MONO MAP
INDEX COUNTER
(0-31)

RE!ET

OVERLAY
REPLACE
COMPLEMENT

PATTERN
REGISTER
(1 X 8)

OUT

oJ"

SHIFT
CLOCK

DATA

BIT MAP
(2/4 PLANES)

WRITE
ENABLE

{

PATTERN MULTIPLIER

53/16
51/M7

L
/4

GREEN
/

~RESS (16 X4)

~
MAP
SELECT

L
/4

COLOR
MAP
RED
(16 X 4)

MONO
(16 X 4)

CONTROLLED FUNCTION

MEDIUM/HIGH RESOLUTION MODE

WORD/VECTOR MODE

READBACK MODE PLANE SELECT (LSB)

READBACK MODE PLANE SELECT (MSB)

WRITE/READ MODE

SCROLL MAP UPDATE

INTERRUPT REQUEST

VIDEO OUTPUT DATA BLANKING

r - - ------- I
I

/
/4

"%
1

LOGIC UNIT

ALU
FUNCTION
(1 X 2)

WRITE BUFFER (INDEX COUNTER CLEAR)

BLUE
(16 X 4)

WRITE
ENABLE

WRITE 8UFFER
INDEX COUNTER
(0-15)

PIXEL
PLANE

PLANE

PLANE
SELECT
(1 X4)

REtET

ENAB~
-

CLOCK

53'"

}--

53/16
51/M4

BIT

SELECTED AREA

~ SELECT

/
51/M5

READ
ENABLE

t P~N'

WRITE MASK
(2 X 8)

SCROLL
MAP
(256 X 8)

wb.:,

53/16
51/M1

READ BACK
LATCH
(2 X 8)

LOAD

MODE REGISTER

INDIRECT REGISTER

RESET

LOAD

BIT

BLUE

~ II

2
GREEN

D/A.......

D/A

L
/4

10
3

I
I

RED

11
4

GRAPHICS

GREEN
SHIELD

RED
SHIELD

MONO
SHIELD

MONO
12

ICOMPOSITE JD/ A
VIDEO

BLUE
SHIELD

I ~'~~
SELECT

5
N/C-

~
6

OA/D2
I

r-L-{
53/16
51/M1

\
/

I
I

KBD/RCV

7
KBD/TXD

RAINBOW 100 GRAPHICS OPTION

I
I
I
I
I
I
I
I
I
I

I
I
~
_V.J
--15

IMOT~B~ _ _

+12

FOREGROUND}BACKGROUND
REGISTER (2 X 4)

\.V

Figure 15. Rainbow Graphics Option -

Block Diagram

8-3

Getting Help

Help Line Phone Numbers
country

Phone Number

U.S.A.

(800) DEC-8000

Canada
United Kingdom

(800) 267-5251

Belgium

(02)-24 26 790

West Germany
Italy

(089) 95 91 66 44

Japan

(0424) 64-3302

Denmark
Spain

(04)-30 10 05

Finland

(90)-42 33 32

Holland

(1820)-31 100

Switzerland

(01)-810 51 21

Sweden
Norway

(02)-25 64 22

France

(1)-687 31 52

Austria

(222)-67 76 41 extension 444

Australia
Sydney
All other areas

(02) 412-5555
(008) 226377

(0256) 59 200

(02)-617 53 81 or 617 53 82

(1)-73 34 307

(08)-98 88 35

C-l

(

Index

A
Address conversion
from pixel coordinates 3-5
Address logic 3-2
Altitude specifications 1-2
ALU functions
COMPLEMENT 4-8, 4-18
OVERLAY 4-9,4-19
REPLACE 4-8, 4-18
ALU/PS Register 4-8, 6-1
bit definitions 13-9
load data 13-9
select 13-9
Arithmetic Logic Unit 4-8

B
Background Register 4-6
BCTRL command 15-9
Bit definitions
ALU/PS Register 13-9
BCTRL command 15-9
CCHAR command 15-3
CURS command 15-10
FIFO Buffer 14-2
FIGS command 15-18

Foreground/Background Register
13-8
GDC Status Register 14-1
Indirect addressing 4-2
Indirect Register 13-3
MASK command 15-22
Mode Register 13-11
PITCH command 15-11
PRAM command 15-12
RDAT command 15-24
RESET command 15-4
Status Register 14-1
SYNC command 15-6
VSYNC command 15-8
WDAT command 15-23
Write Mask Registers 13-5
ZOOM command 15-16
Bitmap 1-2
data 3-6
line address 13-12
modifications 12-3
organization 3-5
reading from 10-1
refreshing 12-1
Bitmap planes
high resolution 3-6
medium resolution 3-6

1-1

Index

c
CCHAR command 15-3
initial value 5-8
Character
characteristics 15-3
Characteristics of
character 15-3
cursor 15-3
Circle
display a 8-9
Clear index counter
Color Map 13-10
Scroll Map 13-12
Write Buffer 13-4
Clock interrupt
parameters 12-2
types 12-2
vector addresses 12-2
Clock interrupts 12-2
Clocks
Graphics Option 12-2
motherboard 12-2
Color intensities 4-9
available 1-1
conversion to drive voltages 4-13
displayed 1-1
Color Map 3-6, 4-9
high resolution 4-11
load data 13-10
loading 4-12
medium resolution 4-10
select 13-10
Color monitor 2-3
Components
hardware 1-1
Configuration
Color Map 4-9
Configurations
color monitor 2-3
dual monitors 2-4
monochrome monitor 2-2
Control display blanking 15-9
Control graphics output 5-24
Control multiple GDCs 15-8
Conversion
color intensities to drive voltages
4-13

1-2

Conversion table
color intensities to drive voltages
4-13
CURS command 15-10
Cursor
characteristics 15-3
positioning 15-10

D
Data flow in FIFO Buffer 14-2
Data logic 3-2
Data path
color monitor 2-3
dual monitors 2-4
monochrome monitor 2-2
Data patterns 3-2
Data read commands 15-2
Digital-to-analog converters 4-13
Disable
individual bits 4-4
plane writes 4-8
Display
a circle 8-9
a pixel 8-4
a vector 8-5
Display blanking 15-9
Display control commands 15-1
Display logic 3-6
Display memory 1-2, 3-2
GDC access to 3-3
organization 3-5
Display planes 1-2
Displaying data from memory 7-1
Drawing control commands 15-2
Dual monitors 2-4

E
Enable
individual bits 4-4
plane writes 4-8
End idle mode 15-15
Environmental specifications 1-1
Examples
CCP/M version test 5-5
CP/M version test 5-2
disable monitor output 5-25

Index

display a circle 8-9
display a pixel 8-4
display a vector 8-6
display data from memory 7-1
enable monitor output 5-24
horizontal scrolling 11-4
initialize Graphics Option 5-9
load Color Map 5-26
loading AL UIPS Register 6-1
loading Foreground/Background Register 6-2
loading Pattern Multiplier 8-3
loading Pattern Register 8-1
modify color data 5-26
MS-DOS version test 5-3
no-op word write 10-5
option present test 5-1
read entire bitmap 10-2
set area to a color 7-4
vertical scrolling 11-2
write a text string 9-38
writing byte-aligned character 9-1

F
FIFO Buffer 3-9, 14-2
bit definitions 14-2
data flow 14-2
flag bit 3-9
read mode 3-9
write mode 3-9
FIGD command 15-17
FIGS command 15-18
Figure drawing parameters 15-18
Foreground Register 4-6
Foreground/Background Register 4-6,
6-2
bit definitions 13-8
load data 13-8
select 13-8
Full-screen scrolling 4-16

G
GCHRD command 15-21
GDC 1-1
command processor 14-2
in native mode 12-3
initialize 5-7
GDC access to bitmap 3-7
GDC addresses 3-5
GDC buffers
reference data 14-1
GDC command bytes 3-9
GDC command logic 3-9
GDC commands 15-1
BCTRL 15-9
CCHAR 15-3
CURS 15-10
FIGD 15-17
FIGS 15-18
GCHRD 15-21
in FIFO Buffer 14-2
MASK 15-22
PITCH 15-11
PRAM 15-12
RDAT 15-24
RESET 12-2, 15-4
START 15-15
SYNC 15-6
VSYNC 15-8
WDAT 15-23
ZOOM 15-16
GDC functions 1-2
GDC line address 13-12
GDC Mask Register 15-22
GDC parameter bytes 3-9
GDC parameters
in FIFO Buffer 14-2
GDC registers
reference data 14-1
GDC reset 5-6, 12-2
parameters 5-6
GDC Status Register
bit definitions 14-1
Graphics Display Controller 1-1

1-3

Index

Graphics Option 1-1
I/O ports 13-1
in vector mode 12-3
in word mode 12-3
initialize 5-8
regulations 1-2
reset 12-2
standards 1-2
Graphics option
reference data 13-1
Graphics output
control of 5-24

H
Hardware components 1-1
High resolution 1-3
refresh 12-1
Horizontal Back Porch 3-7
Horizontal Front Porch 3-7
Horizontal pitch 15-11
Horizontal retrace 3-7
Horizontal scrolling 11-4
Humidity specifications 1-1

I/O ports 4-1, 13-1
Index counter
Write Buffer 4-2
Indirect addressing 4-2
bit definitions 4-2
Indirect Register 4-2
bit definitions 13-3
load data 13-3
Initial values
CCHAR command 5-8
PITCH command 5-8
PRAM command 5-8
ZOOM command 5-7
Initialize
GDC 5-7
Graphics Option 5-8
Intensity values
conversion to drive voltages 4-13
Interrupt control 4-15, 4-19

1-4

L
Line address
bitmap 13-12
GDC 13-12
Load
ALU/PS Register 6-1
Foreground/Background Register 6-2
Pattern Multiplier 8-3
Pattern Register 8-1
Load data
ALU/PS Register 13-9
Color Map 13-10
Foreground/Background Register
13-8
Indirect Register 13-3
Mode Register 13-11
Pattern Multiplier 13-7
Pattern Register 13-6
Scroll Map 13-12
Write Buffer 13-4
Write Mask Registers 13-5
Load GDC Mask Register 15-22
Load parameter RAM 15-12
Loading
Color Map 4-12, 5-25
Scroll Map 4-17
Write Buffer 4-3
Write Mask Registers 4-4

M
Magnification factor 15-16
MASK command 15-22
Medium resolution 1-3
refresh 12-1
Mode
readback 1-3
scroll 1-3
vector 1-3, 3-2
word 1-3, 3-2
Mode Register 4-15, 4-19
bit definitions 13-11
load data 13-11
select 13-11
Model A motherboard 1-1
Model B motherboard 1-1
Modify color data 5-26
Monitor configurations 2-1
Monochrome monitor 2-2

Index

Motherboard
Model A 1-1
Model B 1-1
Multiple GDCs 15-8

o
Operating mode 4-15, 4-19
Operational requirements 12-3
Option
components 4-1
kit numbers 1-3
part numbers 1-3
Option specifications
altitude 1-2
environmental 1-1
humidity 1-1
physical 1-1
power requirements 1-2
temperature 1-1
Organization
bitmap 3-5
Overview 1-1

p
Parameter RAM 15-12
Parameters
clock interrupt 12-2
Pattern Generator 4-5, 8-1
schematic 4-5
shift frequency 4-6
Pattern Multiplier 4-5
load data 13-7
loading 8-3
select 13-7
Pattern Register 4-5, 8-1
load data 13-6
loading 8-1
select 13-6
Persistence
of screen data 11-4
Physical specifications 1-1
PITCH command 15-11
initial value 5-8

Pixel
address 3-5
display a 8-4
Plane select function 4-8
Power requirement specifications 1-2
PRAM command 15-12
initial value 5-8
Programming the Scroll Map 11-1

R
RDAT command 15-24
Read from display memory 15-24
Read operation 10-1
Readback mode 1-3,4-15,4-19
Reading
entire bitmap 10-1
precaution 10-5
Reference data
GDC buffers 14-1
GDC registers 14-1
graphics option buffers 13-1
graphics option maps 13-1
graphics option registers 13-1
Refreshing
bitmap 12-1
in high resolution 12-1
in medium resolution 12-1
Registers
ALU/PS 4-8
Foreground/Background 4-6
Indirect 4-2
Mode 4-15,4-19
Pattern 4-5
Write Mask 4-4
Requirements
operational 12-3
Reset
GDC 12-2
Graphics Option 12-2
RESET command 12-2, 15-4
Reset GDC 5-6
Reset the GDC 15-4
Resolution
high 1-3
medium 1-3
Resolution mode 4-15, 4-19

1-5

Index

s
Scan line
definition 3-5
Screen control parameters 3-7
Screen data persistence 11-4
Screen logic 3-7
Scroll Map 3-5, 4-16
load data 13-12
loading 4-17
operations 11-1
programming 11-1
select 13-12
shadow image 4-17
Scroll Map control 4-15, 4-19
Scroll mode 1-3
Scrolling
horizontal 11-4
vertical 11-1
Select
ALU/PS Register 13-9
Color Map 13-10
Foreground/Background Register
13-8
Mode Register 13-11
Pattern Multiplier 13-7
Pattern Register 13-6
Scroll Map 13-12
Write Buffer 13-4
Write Mask Registers 13-5
Set area to a color 7-4
SET-UP key 12-3
Set-up mode 12-3
Shadow areas 12-1
Shadow color map 5-26
Shadow image
Scroll Map 4-17
Shadowing
Color Map 12-1
Scroll Map 12-1
Software logic 3-1
Split -screen scrolling 4-16
START command 15-15
Start display 15-15
Start figure drawing 15-17
Start graphics area fill 15-21
Start graphics character draw 15-21
Status Register
bit definitions 14-1

1-6

SYNC command 5-8, 15-6
Sync format 15-6
System in set-up mode 12-3
System maintenance port 2-1

T
Temperature specifications 1-1
Test for motherboard version 5-2
Test for option present 5-1
Timing considerations 12-5

v
Vector
display a 8-5
Vector mode 1-3, 3-2
Vertical
retrace 3-7
scrolling 4-16, 11-1
Vertical Back Porch 3-7
Vertical Front Porch 3-7
Video control commands 15-1
Video display
organization 3-2
Video drive voltages 4-13
Video output control 4-15, 4-20
VSYNC command 5-8, 15-8

w
WDAT command 5-7, 15-23
Word address 3-5
Word mode 1-3, 3-2
Write Buffer 4-2
clear index counter 13-4
index counter 4-2
load data 13-4
loading 4-3
output 4-3
select 13-4
Write byte-aligned character 9-1
Write Mask Registers 3-5, 4-4
bit definitions 13-5
load data 13-5
loading 4-4
select 13-5

Index

Write mode 4-15, 4-19
Write operations 3-1
Write text string 9-38
Write to display memory 15-23
Writing depth 3-1
Writing length 3-1
Writing time 3-1
Writing width 3-1

z
ZOOM command 15-16
initial value 5-7
Zoom factor 15-16

1-7

HOW TO ORDER
ADDITIONAL DOCUMENTATION
If you want to order additional documentation by phone:

And you live in:

Call:

Between the hours of:

New Hampshire, Alaska or
Hawaii

603-884-6660

8:30 AM and 6:00 PM
Eastern Time

Continental USA or Puerto Rico

1-800-258-1710

8:30 AM and 6:00PM
Eastern Time

Canada (Ottawa-Hull)

613-234-7726

8:00 AM and 5:00 PM
Eastern Time

Canada (British Columbia)

1-800-267-6146

8:00 AM and 5:00 PM
Eastern Time

Canada (all other)

112-800-267 -6146

8:00 AM and 5:00 PM
Eastern Time

If you want to order additional documentation by direct mail:

And you live in:

Write to:

USA or Puerto Rico

DIGITAL EQUIPMENT CORPORATION
ATTN: Peripherals and Supplies Group
P.O. Box CS2008
Nashua, NH 03061
NOTE: Prepaid orders from Puerto Rico must be
placed with the local DIGITAL subsidiary
(Phone 809-754-7575)
DIGITAL EQUIPMENT OF CANADA LTD.
940 Belfast Road
Ottawa, Ontario K1G 4C2
Attn: P&SG Business Manager
DIGIT AL EQUIPMENT CORPORATION
Peripherals and Supplies Group
P&SG Business Manager
clo Digital's local subsidiary or approved distributor

Canada

Other than USA,
Puerto Rico or Canada

TO ORDER MANUALS WITH EK PART NUMBERS
WRITE OR CALL
P&CS PUBLICATIONS
Circulation Services
10 Forbes Road
NR03/W3
Northboro, Massachusetts 01532
(617)351-4325

RainbowTM
Color/Graphics Option
Programmer's Reference Guide

AA-AE36A-TV

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