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EK-RX01-OP-001

November 1976

64 pages

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Document:	RX8/RX11 Floppy Disk System User's Manual
Order Number:	EK-RX01-OP
Revision:	001
Pages:	64
Original Filename:

OCR Text

RX8/RX11
floppy disk system
/ user's manual

EK-RX01-0P-001

digital equipment corporation • maynard, massachusetts

1st Edition, November 1976

Copyright © 1976 by Digital Equipment Corporation
The material in this manual is for informational
purposes and is subject to change without notice.
Digital Equipment Corporation assumes no responsibility for any errors which may appear in this
manual.
Printed in U.S.A.

The following are trademarks of Digital Equipment
Corporation, Maynard, Massachusetts:
DEC
DECCOMM
DECsystem-IO
DECSYSTEM-20

DEC tape
DECUS
DIGITAL
MASSBUS

PDP
RSTS
TYPESET-8
TYPESET-II
UNIBUS

CONTENTS
Page
CHAPTER 1

GENERAL INFORMATION

1.1
1.2
1.2.1
1.2.2
1.2.3
1.2.4
1.2.5
1.3
1.3.1
1.3.2
1.3.3
1.3.3.1
1.3.3.2
1.3.3.3
1.3.3.4
1.4
1.5
1.6

INTRODUCTION . . . . .
PHYSICAL DESCRIPTION
RX8E/RX11 Interfaces
Microprogrammed Controller
Read/Write Electronics .
Electro-Mechanical Drive
Power Supply
SYSTEMS COMPATIBILITY
Media
Recording Scheme
Logical Format ..
Header Description
Data Field Description
.....
Track Usage
CRC Capability
APPLICABLE INSTRUCTION MANUALS
CONFIGURATION
SPECIFICATIONS . . . . . . . . . .

CHAPTER 2

INSTALLATION AND OPERATION

2.1
2.2
2.2.1
2.2.2
2.2.3
2.2.4
2.3
2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
2.4
2.4.1
2.4.2
2.4.3
2.4.3.1
2.4.3.2
2.4.4
2.5
2.5.1
2.5.2
2.5.3
2.5.3.1
2.5.3.2
2.5.4

PURPOSE AND ORGANIZATION
SITE PREPARATION
Space ..
Cabling . . . . .
AC Power
Fire and Safety Precautions
ENV1RONMENTAL CONSIDERATIONS
General . . . . . . . . . . . . .
Temperature, Relative Humidity
Heat Dissipation
Radiated Emissions
Cleanliness
INST ALLATION
General ..
Tools . . .
Unpacking and Inspection
Cabinet-Mounted .
Separate Container
Installation . . .
OPERATION
....... .
Operator Control . . . .
Diskette Handling Practices and Precautions
Diskette Storage . . . . . . . . . . . . . .
Short Term (Available for Immediate Use)
Long Term .
Shipping Diskettes . . . . . . . . . . . . . . .

iii

1-1
1-1
1-2
1-2
1-2
1-2
1-3
1-3
1-3
1-10
1-10
1-10
1-11
1-11

1-12
1-12
1-12
1-13

2-1
2-1
2-1
2-1
2-1
2-2
2-2
2-2
2-3
2-4 2-4

2-4
2-4

2-4
2-4
2-4
24
2-6
2-6
2-8
2-8
2-8
2-12
2-12
2-12

2-12

CONTENTS (Cont)

Page
CHAPTER 3

RX 11 INTERFACE PROGRAMMING INFORMATION

3.1
3.2
3.2.1
3.2.2
3.2.2.1
3.2.2.2
3.2.2.3
3.2.2.4
3.3
3.3.1
3.3.2
3.3.3
3.3.4
3.3.5
3.3.6
3.3.7
3.3.8
3.4
3.4.1
3.4.2
3.4.3
3.5
3.6

REGISTER AND VECTOR ADDRESSES .,
REGISTER DESCRIPTION . . . . . . . . .
RXCS - Command and Status (177170)
RXDB - Data Buffer Register (I77172)
RXT A - RX Track Address
RXSA - RX Sector Address
RXDB - RX Data Buffer
RXES - RX Error and Status
FUNCTION CODES
Fill Buffer (000) ..
Empty Buffer (001)
Write Sector (010)
Read Sector (011)
Read Status (I 01)
Write Sector with Deleted Data (110)
Read Error Register Function (I 1 1)
Power Fail . . . . . . .
PROG RAMMING EXAMPLES
Read Data/Write Data
Empty Buffer Function
Fill Buffer Function
RESTRICTIONS AND PROGRAMMING PITFALLS
ERROR RECOVERY . . . . . . . . . . . . . . . .

CHAPTER 4

RX8E INTERFACE PROGRAMMING INFORMATION

4.1

DEVICE CODES . . . . . .
INSTRUCTION SET . . . . . . . .
Load Command (LCD) . . . .
Transfer Data Register (XDR)
STR
SER
SDN
INTR
INIT
REGISTER DESCRIPTION
Command Register ..
Error Code Register
RXT A - RX Track Address
RXSA - RX Sector Address
RXDB - RX Data Buffer
RX Error and Status . . . .
FUNCTION CODE DESCRIPTION
Fill Buffer (000) ..
Empty Buffer (001)
Write Sector (010)
Read Sector (011)
Read Status (I 0 1)

4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.2.6
4.2.7
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.3.5
4.3.6
4.4
4.4.1
4.4.2
4.4.3
4.4.4
4.4.5

3-1
3-2
3-2

3-3
3-3
3-3

3-4
3-4
3-5
3-5
3-5
3-6
3-6
3-7
3-7
3-7
3-7
3-8
3-8
3-8
. 3-11
. 3-11
.. 3-11

4-1
4-2
4-2
4-2

4·3
4-3

4-3
4-3

4-3
4-3
4-3

4-4
4-5
4-5
4-6
4-6
4-7
4-7
4-8
4-8
4-9
4-9

CONTENTS (Cont)
Page

4.4.6
4.4.7
4.4.8
4.S
4.S.1
4.S.2
4.S.3
4.6
4.7

Write Deleted Data Sector (110) ..
Read Error Register Function (111)
Power Fail . . . . . . . . . . . . .
PROG RAMMING EXAMPLES
.... .
Write/Write Deleted Data/Read Functions
Empty Buffer Function . . . . . . . . .
Fill Buffer Function . . . . . . . . . . .
RESTRICTIONS AND PROGRAMMING PITFALLS
ERROR RECOVERY
. . . . . . . ....

4-9
4-9
4-9
· 4-10
· 4-10
· 4-10
· 4-10
· 4-1S
· 4-16

ILLUSTRA nONS
Figure No.
1-1
1-2
1-3
1-4
l-S
1-6
1-7
1-8
1-9

1-10
1-11
2-1

2-2
2-3

2-4
2-S
2-6
2-7
3-1
3-2
3-3
3-4
3-S
3-6
3-7
3-8
4-1
4-2
4-3

4-4
4-S
4-6
4-7
4-8

4-9
4-10

Title
Floppy Disk System Configuration
Front View of the Floppy Disk System
M83S7 Module (RX8E Interface)
M7846 Module (RX 11 Interface)
Top View of the RXO 1
Underside View of Drive
Top View of Drive
Diskette Media . . . . .
Flux Reversal Patterns
Track Format (Each Track)
Sector Format (Each Sector)
RX01
.......... .
Cabinet Layout Dimensions
RXOI Shipping Restraints
RX8/RX 11 Unpacking . . .
RXOI Cabinet Mounting Information
Cable Routing, BCOSL-IS
Flexible Diskette Insertion
RXCS Format (RX11)
RXTA Format (RXl1)
RXSA Format (RXl1)
RXDB Format (RX 11)
RXES Format (RX11)
RX11 Write/Write Deleted Data/Read Example
RX 11 Empty Buffer Example
RXll Fill Buffer Example . . . . .
LCD Word Format (RX8E)
Command Register Format (RX8E)
Error Code Register Format
RXTA Format (RX8E)
RXSA Format (RX8E)
RXDB Format (RX8E)
RXES Format (RX8E)
RX8E Write/Write Deleted Data/Read Example
RX8E Empty Buffer Example
Fill Buffer Example . . . . . . . . . . . . . .

Page

1-2
1-3

1-4
l-S
1-6
1-7
1-8
1-9

1-10
1-10
1-11

2-2
2-3
2-S
2-7

2-8
2-9

2-11
3-2
3-3
3-3
3-4
3-4

3-9
· 3-10
3-13
4-2
4-3

4-4
4-S
4-S
4-6
4-6
· 4-11

· 4-13
· 4-14

TABLES
Title

Table No.
2-1
4-1

Page
2-10

Interface Code/Jumper Configura tion
Device Code Switch Selection

4-1

CHAPTER 1
GENERAL INFORMATION
This manual presents information on the installation, operation, and programming of the RX8 or RXll Floppy Disk
System. Chapter 2 (Installation and Operation) should be consulted for unpacking and installation information.
Chapter 2 also provides information on the proper care of the media and should be read carefully.
1.1

INTRODUCTION

The RX8 and RXII Floppy Disk Systems consist of an RXOI subsystem and either an RX8E interface for a PDP-8
system or an RXII interface for a PDP-II system.
The RXOI is a low cost, random access, mass memory device that stores data in fixed length blocks on a
preformatted, IBM-compatible, flexible diskette. Each drive can store and retrieve up to 256K 8-bit bytes of data
(pDP-II or PDP-8) or I28K 12-bit words (PDP-8). The RXOI consists of one or two flexible disk drives, a single
read/write electronics module, a microprogrammed controller module, and a power supply, enclosed in a
rack-mountable, 10-1/2 inch, self-cooled chassis. A cable is included for connection to either a PDP-8 interface
module for use on the PDP-8 Omnibus or a PDP-II interface for use on the PDP-II Unibus.
The RXOI performs implied seeks. Given an absolute sector address, the RXOI locates the desired sector and
performs the indicated function, including automatic head position verification and hardware calculation and
verification of the Cyclic Redundancy Check (CRC) character. The CRC character that is read and generated is
compatible with IBM 3740 equipment.
The RXOI connects to the M8357 Omnibus interface module, which converts the RXOI I/O bus to a PDP-8 family
Omnibus structure. It controls interrupts to the CPU initiated by the RXOI, controls data interchange between the
RXOI and the host CPU, and handles I/O transfers used to test status conditions.
The RXOI connects to the M7846 Unibus interface module, which converts the RXOI I/O bus to a PDP-II Unibus
structure. It controls interrupts to the CPU initiated by the RXO I, decodes Unibus addresses for register selection,
and handles data interchange between the RXOI and the host CPU.
The interface modules are dc powered by their host processor.
1.2 PHYSICAL DESCRIPTION

A complete system consists of the following components:
M7726 controller module
M7727 read/write electronics module
H77I A or B power supply
RXOI-CA floppy disk drive (60 Hz, max of 2)
RXOI-CC floppy disk drive (50 Hz, max of 2)
M8357 (RX8E) or M7846 (RXIl) interfaces

1-1

All components except the interface arc housed in a 10-1/2 in. rack-mountable box. The power supply, M7726
module, and M7727 module are mounted above the drives. Interconnection from the RXOI to the interface is with a
40-conductor BC05L-15 cable of standard length (IS ft). Figure 1-1 is a configuration drawing of the system, and
Figure 1-2 is a front view of a dual drive system.

DR IVE # 0

DISKETTE

M8357
OMNIBUS
INTERFACE

0
M
N
I
B
U
S

M7846
UNI BUS
INTERFACE

U
N
I
B
U
S

fL CPU
CONTROLLER
M7726

DRIVE
ELECTRONICS
M7727

DRIVE #1

DISKETTE

CP-1505

Figure 1-1

Floppy Disk System Configuration

1.2.1 RX8E/RX 11 Interfaces
Interface modules M8357 (RX8E) and M7846 (RXII) arc both quad modules. The M8357 plugs into an Omnibus
slot and allows the RXOl to be used on the PDP-8 processors. The M7846 plugs into an SPC (small peripheral
controller) slot with any PDP-II processor. Figure 1-3 sh ows the M8357 module and its major sections. Figure 14
shows the M7846 module and its major sections.

1.2.2 Microprogrammed Controller
The M7726 microprogrammed controller module is located in the RXOI cabinet as shown in Figure 1-5. The M7726
is hinged on the left side and lifts up for access to the M7727 read/write electronics module.

1.2.3 Read/Write Electronics
TIle M7727 read/write electronics module is located in the RXOI cabinet as shown in Figure 1-5.

1.2.4 Electro-Mechanical Drive
A maximum of two drives can be attached to the read/write electronics. The electro-mechanical drives are mounted
side by side under the read/write electronics board (M7727). Figure 1-6, which is an underside view of the drive,
shows the drive motor connected to the spindle by a belt. (This belt and the small pulley are different on the 50 Hz
and 60 Hz units; see Paragraph 2.2.3.2 for complete input power modification requirements.) Figure 1-7 is the top
view showing the electro-mechanical components of the drive.

1-2

7408-1

Figure 1-2 Front View of the Floppy Disk System
1.2.S Power Supply
The H771 power supply is mounted at the rear of the RXOI cabinet as shown in Figure 1-5. The H771A is rated at
60 Hz ± 1/2 Hz over a voltage range of 90-132 Vac. TheH771C and Dare rated at 50 Hz ± 1/2 Hz over four voltage
ranges:
90-120 Vac }
3.5 A circuit breaker; H771C
100-132 Vac
180-240 Vac }
1.75 A circuit breaker; H771D
200-264 Vac
Two power harnesses are provided to adapt the H771C or D to each voltage range. This is not applicable to the
H771A. See Paragraph 2.2.3.2 for complete input power modification requirements.
1.3 SYSTEMS COMPATIBILITY
This section describes the physical, electrical, and logical aspects of IBM compatibility as defined for data
interchange with IBM system 3740 devices.
1.3.1 Media
The media used on the RX8 or RXl1 Floppy Disk System is compatible with the IBM 3740 family of equipment
and is shown in Figure 1-8.
The "diskette" media was designed by applying tape technology to disk architecture. This resulted in a flexible
oxide-on-mylar surface encased in a plastic envelope with a hole for the read/write head, a hole for the drive spindle
hub, and a hole for the hard index mark. The envelope is lined with a fiber material that cleans the diskette surface.
The media is supplied to the customer preformatted and pretested.
1-3

BC05L·15
INTERFACE
CABLE
CONNECTOR

DEVICE
CODE
SWITCHES

7408-3

Figure 1·3 M8357 Module (RX8E Interface)

1-4

CONNECTOR
FOR THE
BC05L-15
INTERFACE
CABLE

PRIORITY
PLUG

RX11
INTERFACE
REGISTER

Figure 14 M7846 Module (RXll Interface)

1-5

7408-4

M7726 J.LCPU
CONTROLLER
MODULE

BC05L-15
INTERFACE
CABLE
M7727
READIWRITE
ELECTRONICS
MODULE

H771
POWER
SUPPLY

7408-8

Figure 1-5 Top View of the RXOI

1-6

DRIVE MOTOR
BELT

DRIVE SPINDLE
PULLEY

AC
POWER
CONNECTOR

DC
STEPPER
MOTOR

7408-5

Figure 1-6 Underside View of Drive

1-7

READ/WRITE
HEAD

HEAD LOAD
ARM

HELIX
DRIVE

7408-7

Figure 1-7 Top View of Drive

1-8

INDEX HOLE

REGISTRATION
HOLE

READ/WRITE
HEAD
APERTURE
7408-2

Figure 1·8 Diskette Media

1-9

1.3.2 Recording Scheme
The recording scheme used is "double frequency." In this method, data is recorded between bits of a constant clock
stream. The clock stream consists of a continuous pattern of 1 flux reversal every 4 J.1s (Figure 1-9). A data "one" is
indicated by an additional reversal between clocks (i.e., doubling the bit stream frequency; hence the name). A data
"zero" is indicated by no flux reversal between clocks.
A continuous stream of ones, shown in the bottom waveform in Figure 1-9, would appear as a "2F" bit stream, and
a continuous stream of zeros, shown in the top waveform in Figure 1-9, would appear as a "1 F" or fundamental
frequency bit stream.

ALL ZEROS
PATTERN
0

0
I

~CHANGING
PATTERN

I
I

~ 4}'sec

I
I

ALL ONES
PATTERN

1
1

I.-

CP-1506

Figure 1-9 Flux Reversal Patterns
1.3.3 Logical Fonnat
The logical format of the RX8 and RXll Floppy Disk Systems is the same as that used in the IBM 3740.
Data is recorded on only one side of the diskette. This surface is divided into 77 concentric circles or "tracks"
numbered 0-76. Each track is divided into 26 sectors numbered 1-26 (Figure 1-10). Each sector contains two
major fields: the header field and the data field (Figure 1-1 O.

L.E.D. TRANSDUCER OUTPUT

""--H-A-R-Z.D--.,

f'~1_ _ _...J
I

I~g~~

L..---------------III

PRE-INDEX
IS ECTOR
GAP
#26 ~20BYTES

SECTOR
#1

SECTOR
#2

SECTOR
#3

SECTOR
#4

CP ·1507

SOFT INDEX MARK
1 BYTE
-

ROTATION

Figure 1-10 Track Format (Each Track)
1.3.3.1 Header Description - The header field is broken into seven bytes (eight bits/byte) of information and is
preceded by a field of zeros for synchronization.
1.

Byte No.1: ID Address Mark - This is a unique stream of flux reversals (not a string of data bits) that is
decoded by the controller to identify the beginning of the header field.

Byte No.2: Track Address - This is the absolute (0-1148) binary track address. Each sector contains
track address information to identify its location on 1 of the 77 tracks.

1-10

HEADER FIELD

DATA FIELD

..
~O

ADDRESS
MARK
SYNC
FI ELD
ALL "0'5"
33 BYTES

-Vl
COI'Tl

co •

-In
1'Tl::-:

1'Tl0
;u

I'Tl

;po

--l
CO;U
-<;po

o
o
;u

I'Tl
Vl
Vl

-l !--,

-<0

-<n
-l-l

HEADER
CRC
2 BYTES

-lui
•

DATA MARK
SYNC FIELD
ALL "0'5"
17 BYTES

;po;po
;U-l
::-:;po
-0
CO;U
-<
-lO
I'TlI'Tl
r

128 10 BYTES
OF DATA

I'Tl

-l

DATA
CR C
2 BYTES

I'Tl

o
o;po

-l
;po

..
BYTE

\I BYTES----j.I.---......1

~. WRITE GATE TURN OFF
L FOR WRITE OF PRECEEDING

1---6 BYTES

WRITEGATETURNON
lFORWRITE OF NEXT
DATA FIELD

DATA FIELD
-

CP-l!lOB

ROTATION

Figure 1-11

Sector Format (Each Sector)

Byte No.3 - Zeros (one byte)

Byte No.4: Sector Address - This is the absolute binary sector address {l-32s). Each sector contains
sector address information to identify its circumferential position on a track.

Byte No.5 - Zeros (one byte)

Bytes No.6 and 7: CRC - This is the Cyclic Redundancy Check character that is calculated for each
sector from the first five header bytes using a polynomial division algorithm designed to detect the types
of failures most likely to occur with "double frequency" recorded data and the floppy media. The CRC
is compatible with IBM 3740 series equipment.

1.3.3.2 Data Field Description - The data field is broken into 131 bytes of information and is preceded by a field
of zeros for synchronization and the header field (Figure 1-11).
1.

Byte No.1: Data or Deleted Data Address Mark - This is a unique string of flux reversals (nofa string
of data bits) that is decoded by the controller to identify the beginning of the data field. The deleted
data mark is not used during normal operation but the RXOI can identify and write deleted data marks
under program control, as required. The deleted data mark is only included in the RX8/RXl1 system to
be IBM compatible. One or the other data address marks precedes each data field.

Bytes No. 2-129 - These bytes comprise the data field used to store 128 8-bit bytes of information.
NOTE
Partial data fields are not recorded.

Bytes No. 130 and 131 - These bytes comprise the CRC character that is calculated for each sector
from the first 129 data field bytes using the industry standard polynomial division algorithm designed to
detect the types of failures most likely to occur in double frequency recording on the floppy media.

1.3.3.3 Track Usage - In the IBM 3740 system, some tracks are commonly designated for special purposes such as
error information, directories, spares, or unused tracks. The RXOI is capable of recreating any system structure
through the use of special systems programs, but normal operation will make use of all the available tracks as data
tracks. Any special file structures must be accomplished through user software.

1-11

1.3.3.4 CRC Capability - Each sector has a two-byte header CRC character and a two-byte data CRC character to
ensure data integrity. The CRC characters are generated by the hardware during a write operation and checked to
ensure all bits were read correctly during a read operation. The CRC character is the same as that used in the IBM
3740 series of equipment.
1.4 APPLICABLE INSTRUCTION MANUALS
This manual is designed to be used in conjunction with the RX8/RX 11 Engineering Drawings. Other documents
useful in operating and understanding the RX8/RXll system are:

PDP-}} * Processor Handbook
PDP-}} Peripherals Handbook
PDP-8 Small Computer Handbook
PDP-8A User Manual
I.5 CONFIGURATION
Option number designations are as follows:
PDP-8 Systems
RX8-AA
RX8-AD
RX8-BA
RX8-BD

Single drive system, 115 V, 60 Hz
Single drive system, 50 Hz
Dual drive system, 115 V /60 Hz
Dual drive system, 50 Hz

PDP-II Systems
RXI1-AA
RXII-AC
RXII-BA
RXll-BD

Single drive system, 115 V/60 Hz
Single drive system, 50 Hz
Dual drive system, 115 Vj60 Hz
Dual drive system, 50 Hz
NOTE
50 Hz versions are available in voltages of 105, 115, 220, 240
Vac by field pluggable conversion. See Paragraph 2.2.3.2 for
complete input power modification requirements.

*Appropriate handbook for the particular processor used with the system.

1-12

1.6 SPECIFICATIONS
System Reliability
Minimum number of revolutions per track

1 million/media (head loaded)

Seek error rate

1 in 10 6 seeks

Soft read error rate

1 in 10 9 bits read

Hard read error rate

1 in 10 1 2 bits read
NOTE
The above error rates only apply to media that is properly
cared for. Seek error and soft read errors are usually
attributable to random effects in the head/media interface,
such as electrical noise, dirt, or dust. Both are called "soft"
errors if the error is recoverable in ten additional tries or less.
"Hard" errors cannot be recovered. Seek error retries should
be preceded by an Initialize.

Drive Performance
Capacity
Per diskette
Per track
Per sector
Data transfer rate
Diskette to con troller buffer
Buffer to CPU interface
CPU interface to I/O bus

8-bit bytes

12-bit words

256,256 bytes
3,328 bytes
128 bytes

128,128 words
1,664 words
64 words

4 J..ls/data bit (250K bps)
2 J..ls/bit (500K bps)
18 J..ls/8-bit byte (>50K bytes/sec)

NOTE
PDP-8 interface can operate in 8- or 12-bit modes under
software control. The transfer rate is 23 J..lS per 12-bit word
(>40K bytes/sec).
Track-to-track move
Head settle time
Rotational speed
Recording surfaces per disk
Tracks per disk
Sectors per track
Recording technique
Bit density
Track density
Average access

10 ms/track maximum
20 ms maximum
360 rpm ± 2.5%; 166 ms/rev nominal
1
77 (0-76) or (0-1148)
26 (1-26) or (1-328)
Double frequency
3200 bpi at inner track
48 tracks/in.
488 ms, computed as follows:
Seek
Settle
Rotate
(77 tks/2) X 10 ms + 20 ms + (166 ms/2) = 488 ms

1-13

Environmental Characteristics
Temperature
RXOI, operating

RXOI, nonoperating

0
0
0
ISO to 32 C (59 to 90 F) ambient; maximum
0
temperature gradient = 20 F/hr (11.1 0 C/hr)
0
0
0
_35 to +60 C (_30 to +1400 F)

Media, operating
Media, nonoperating

0
0
0
-35 0 to +52 C (-30 to +125 F)

NOTE
Media temperature must be within operating temperature
range before use.
Relative humidity
RXOI, operating

0
0
25 C (77 F) maximum wet bulb
0
0
2 C (36 F) minimum dew point
20% to 80% relative humidity

RXOI, nonoperating

5% to 98% relative humidity (no condensation)

Media, nonoperating

10% to 80% relative humidity

Magnetic field

Media exposed to a magnetic field strength of 50 oersteds
or greater may lose data.

Interface modules

Operating temperature
Relative humidity
Maximum wet bulb
Minimum dew point

0
0
0
50 to 50 C (41 to 122 F)
10% to 90%
0
0
32 C (90 F)
0
0
2 C (36 F)

Electrical
Power consumption
RXOI
PDP-II interface (M7846)
PDP-8 interface (M8357)
AC power input

3 A at 24 V (dual), 75W; 5 A at 5 V, 25 W
Not more than 1.5 A at 5 V dc
Not more than 1.5 A at 5 Vdc
4 A at 115 Vac
2 A at 230 Vac

1-14

CHAPTER 2
INSTALLATION AND OPERATION

2.1 PURPOSE AND ORGANIZATION
This chapter provides information on installing and operating the RX8/RXII Floppy Disk System. This information
is organized into four sections as outlined below.
1.

Site Preparation - The planning required to make the installation site suitable for operation of the
floppy disk system, including space, cabling, and power requirements, and fire and safety precautions.

Environmental Considerations - The specific environmental characteristics of the floppy disk systems,
i.e., temperature, relative humidity, air conditioning and/or heat dissipation, and cleanliness.

Installation - The actual step-by-step process of installing the floppy disk system from unpacking
through the preliminary installation checks, power conversion techniques, and acceptance testing.

Operation Practices - The recommended practices for using the floppy disk system, handling the media,
and shipping and storing the diskettes.

2.2 SITE PREPARATION
2.2.1 Space
The RXOI is a cabinet-mountable unit that may be installed in a standard Digital Equipment Corporation cabinet.
This rack-mountable version is approximately 10-1/2 in. (28 cm) high, 19 in. (48 cm) wide, and 16-1/2 in. (42 cm)
deep (Figure 2-1).
Provision should be made for service clearances of approximately 22 in. (56 cm) at the front and rear of the cabinet
(Figure 2-2).

2.2.2 Cabling
The standard interface cable provided with an RX8/RXll (BC05L-15) is 15 ft (4.6 m) in length, and the positioning
of the RXOI in relation to the central processor should be planned to take this into consideration. The RXOI should
be placed near the control console or keyboard so that the operator will have easy access to load or unload disks.
The position immediately above the CPU is preferred. The ac power cord will be about 9 ft (2.7 m) long.

2.2.3 AC Power
2.2.3.1 Power Requirements - The RXOI is designed to use either a 60 Hz or a 50 Hz power source. The 60 Hz
version (RXOI-A) will operate from 90 to 132 Vac, without modifications, and will use less than 4 A operating. The
50 Hz version (RXOI-D) will operate within four voltage ratings and will require field verification/modification to
ensure that the correct voltage option is selected. The voltage ranges of90 to 120 Vac and 180 to 240 Vac will use
less than 4 A operating. The voltage ranges of 100-132 Vac and 200-264 Vac will use less than 2 A. Both versions
of the RXOI will be required to receive the input power from an ac source (e.g., 861 power control) that is
controlled by the system's power switch.
2-1

10.5"

1~11~111~IIIIIIIIIIIIIII~m~ ]orn)
I~

19"
(48.3 cm)

·1

(FRONT VIEW)

17.0"

(43.2 cm)

,.--

-----

~
~

(FRONT)

C-

----

~SEE NOTE

/
\S)

INSIDE TRACK

Cll:::::::::J

26.5"
(66.3 cm)
SIDE VIEW)

NOTE
Dust cover attached to cabinet
not RXOI.

CP-ISII

Figure 2·1

RXO 1

2.2.3.2 Input Power Modification Requirements - The 60 Hz version of the RXO 1 uses the H771 A power supply
and will operate on 90 to 132 Vac, without modification. To convert to operate on a 50 Hz power source in the
field, the H771A supply must be replaced with an H771C or D (Figure 1-5) and the drive motor belt and drive
motor pulley must be replaced (Figure 1-6). The 50 Hz version of the RXO 1 uses either the H771 C or D power
supply. The H771C operates on a 90-120 Vac or 100-132 Vac power source. The H771D operates on a
180-240 Vac or 200-264 Vac power source. To convert the H771C to the higher voltage ranges or the H771D to
the lower voltage ranges, the power harness and circuit breaker must be changed. See Figure 2-3 for appropriate
power harness and circuit breaker.
2.2.4 Fire and Safety Precautions
The RX8/RXII Floppy Disk System presents no additional fire or safety hazards to an existing computer system.
Wiring should be carefully checked, however, to ensure that the capacity is adequate for the added load and for any
contemplated expansion.
2.3 ENVIRONMENTAL CONSIDERATIONS
2.3.1 General
The RX8/RXll is capable of efficient operation in computer environments~ however, the parameters of the
operating environment must be determined by the most restrictive facets of the system, which in this case are the
diskettes.
2-2

SWINGING DOOR
R. H. OR L. H.

18 Y3~
(46.35cm)

REMOVABLE
END PANEL
REMOVABLE
END PANEL-

1--0----------,
I
I

I
I

48 7/32"
(122.47cm)

CABLE ACCESS -

I
I

_ _ _ _ _ _~~_I

FAN
PORTS

,/ :-0--"

30"
(76.2cm)
LEVELER
4 PLACES

+
CASTER SWIVEL
RADIUS 2 13/32"
(6.12 cm)
(4) CASTERS

"".-----21
/16
1..
:

(54.87 cm)

I
II

RXOl EXTENDED
FROM CABINET

(48.~ cm)

L________ J~
CABINET 717/1~(182.28cm) high
(floor line to cabinet top)

CP-1612

Figure 2-2 Cabinet Layout Dimensions
2.3.2 Temperature, Relative Humidity
The operating ambient temperature range of the diskette is 59° to 90° F (15° to 32° C) with a maximum
temperature gradient of 20° F/hr (-6.7° C/hr).
The media nonoperating temperature range (storage) is increased to -30° to 125° F (-34.4° to 51.6° C), but care
must be taken to ensure that the media has stabilized within the operating temperature range before use. This range
will ensure that the media will not be operated above its absolute temperature limit of 125° F.

2-3

Humidity control is important in any system because static electricity can cause errors in any CPU with memory.
The RXOI is designed to operate efficiently within a relative humidity range of 20 to 80 percent, with a maximum
wet bulb temperature of 77° F (25° C) and a maximum dew point of 36° F (2° C).
2.3.3 Heat Dissipation
The heat dissipation factor for the RXOI Floppy Disk System is less than 225 Btu/hr. By adding this figure to the
total heat dissipation for the other system components and then adjusting the result to compensate for such factors
as the number of personnel, the heat radiation from adjoining areas, and sun exposure through windows, the
approximate cooling requirements for the system can be determined. It is advisable to allow a safety margin of at
least 25 percent above the maximum estimated requirements.
2.3.4 Radiated Emissions
Sources of radiation, such as FM, vehicle ignitions, and radar transmitters located close to the computer system, may
affect the performance of the RX8/RXll Floppy Disk System because of the possible adverse effects magnetic
fields can have on diskettes. A magnetic field with an intensity of 50 oersteds or greater might destroy all or some of
the information recorded on the diskette.
2.3.5 Cleanliness
Although cleanliness is important in all facets of a computer system, it is particularly important in the case of
moving magnetic media, such as the RXOI. Diskettes are not sealed units and are vulnerable to dirt. Such minute
obstructions as dust specks or fingerprint smudges may cause data errors. Therefore, the RXO 1 should not be
subjected to unusually contaminated atmospheres, especially one with abrasive airborne particles. (Refer to
Paragraph 2.5.2.)
NOTE
Removable media involve use, handling, and maintenance
which are beyond DEC's direct control. DEC disclaims
responsibility for performance of the equipment when operated with media not meeting DEC specifications or with media
not maintained in accordance with procedures approved by
DEC. DEC shall not be liable for damages to the equipment or
to media resulting from such operation.
2.4 INSTALLATION
2.4.1 General
The RX8/RXII Floppy Disk System can be shipped in a cabinet as an integral part of a system or in a separate
container. If the RXOI is shipped in a cabinet, the cabinet should be positioned in the final installation location
before proceeding with the installation.
2.4.2 Tools
Installation of an RX8/RX 11 Floppy Disk System requires no special tools or equipment. Normal hand tools are all
that are necessary. However, a forklift truck or pallet handling equipment may be needed for receiving and installing
a cabinet-mounted system.
2.4.3 Unpacking and Inspection
2.4.3.1 Cabinet-Mounted
1.

Remove the protective covering over the cabinet.

Remove the restraint on the rear door latch and open the door.

2-4

Remove the two bolts on the cabinet's lower side rails that attach the cabinet to the pallet.

Raise the four levelers at the corners of the cabinet, allowing the cabinet to roll on the casters.

Carefully roll the cabinet off the pallet; if a forklift is available, it should be used to lift and move the
cabinet.

Remove the shipping restraint from the RXOI and save it for possible reuse (Figure 2-3).

Slide the RXOI out on the chassis slides and visually inspect for any damage, loose screws, loose wiring,
etc.
NOTE
If any shipping damage is found, the customer should be
notified at this time so he can contact the carrier, and record
the information on the acceptance form.

JUMPER P1

FILTER

POWER PLUGS

FILTER
7436-12

VOLTAGE (Vac)

POWER HARNESS

CIRCUIT BREAKER

90-120
100-132
180-240
200-264

70-10696-02
70-10696-01
70-10696-04
70-10696-03

3.5 A, 12-12301-01
3.5 A, 12-12301-01
1.75 A, 12-12301-00
1.75 A, 12-12301-00

Figure 2-3 RXOI Shipping Restraints

2-5

2.4.3.2 Separate Container
1.

Open the carton (Figure 2-4) and remove the corrugated packing pieces.

Lift the RXO 1 ou t of the carton and remove the plastic shipping bag.

Remove the shipping fixtures from both sides of the RXOI and inspect for shipping damage.

Attach the inside tracks of the chassis slides provided in the carton to the RXO 1 (Figure 2-1).

Locating the proper holes in the cabinet rails (Figure 2-5), attach the outside tracks to the cabinet.

Place the tracks attached to the RXOI inside the extended cabinet tracks and slide the unit in until the
tracks lock in the extended position.

Locate the RXOI cover in the cabinet above the unit and secure it to the cabinet rails (Figure 2-3).

2.4.4 Installation
1.

Loosen the screws securing the upper module (M7726) and swing it up on the hinge.

Inspect the wiring and connectors for proper routing and ensure that they are seated correctly.

This step is for 50 Hz versions only. Check the power configuration to ensure that the proper power
harness and the correct circuit breaker are installed (Figure 2-3).

Connect the BCOSL-15 cable to the M7726 module and route it through the back of the RXOI (Figure
2-6) to the CPU, then connect it to the interface module (RX8E, M8357; RXll, M7846).

Refer to Table 2-1 for correct device code or addressing jumpers.

Ensure that power for the system is off.

Insert the interface module into the Omnibus (RX8E) or available SPC slot (RX 11). (Refer to PDP-)}
Processor Handbook, SpeCifications, Chapter 9.)

Connect the RXOI ac power cord into a switched power source.

Turn the power on, watching for head movement on the drive(s) during the power up, initialize phase.
The head(s) should move ten tracks toward the center and back to track O.

10.

Perform the diagnostic in the sequence listed below for the number of passes (time) indicated. If any
errors occur, refer to Chapter 6 for corrective action.
RX8 or RX II Diagnostic - 2 passes
Data Reliability /Exerciser - 3 passes
DECX-8 or DECX-II - 10 minutes

2-6

SLIDES

ONE PIECE
FOLDER

9905711

PLYWOOD HOLDING
FIXTURE RT. SI DE

9905712-01

FLAT WASHER (8)

RXOI

,,-/ 90- 09024-00
(I,

DUST
COVER

LOCK WASHER (8)

~~ 90-07906-00

~SCREW (8)
90- 06076-01

SLOTTED

SHIPPING
CARTON

CP-l!196

Figure 2-4 RX8/RXll Unpacking

2-7

COVER

SCREWS,
CHASSIS SLIDES

o
o
CP-1594

Figure 2-5 RX01 Cabinet Mounting Information

2.5 OPERATION
2.5.1 Operator Control
The simplicity of the RX01 precludes the necessity of operator controls and indicators. A convenient method of
opening the unit for diskette insertion and removal is provided. On each drive is a simple pushbutton, which is
compressed to allow the spring-loaded front cover to open. The diskette may be inserted or removed, as shown in
Figure 2-7, with the label up. The front cover will automatically lock when the bar is pushed down.
CAUTION
The drive(s) should not be opened while they are being
accessed because data may be incorrectly recorded, resulting in
a CRC error when the sector is read.
2.5.2 Diskette Handling Practices and Precautions
To prolong the diskette life and prevent errors when recording or reading, reasonable care should be taken when
handling the media. The following handling recommendations should be followed to prevent unnecessary loss of
data or interruptions of system operation.
1.

Do not write on the envelope containing the diskette. Write any information on a label prior to affixing
it to the diskette.

Paper clips should not be used on the diskette.

Do not use writing instruments that leave flakes, such as lead or grease pencils, on the jacket of the
media.

2-8

7436-18

Figure 2-6 Cable Routing, BCOSLIS

2-9

Table 2-1
Interface Code/Jumper Configuration
RXll (M7846)

BR Priority
BR7 - 54-08782
BR6 - 54-08780
*BR5 - 54-08778
BR4 - 57-08776
RX8E (M8357)
Device Codes
*670X
671X
672X
673X
674X
675X
676X
677X

SWI

SW2

SW3

SW4

SW5

SW6

ON
ON
ON
ON
OFF
OFF
OFF
OFF

ON
ON
OFF
OFF
ON
ON
OFF
OFF

ON
OFF
ON
OFF
ON
OFF
ON
OFF

OFF
OFF
OFF
OFF
ON
ON
ON
ON

OFF
OFF
ON
ON
OFF
OFF
ON
ON

OFF
ON
OFF
ON
OFF
ON
OFF
ON

*Unihus Address 17717X
AI2/WI8 - Removed
AII/WI7 - Removed
AI0/WI6 - Removed
A9/W 15 - Removed
A8/WI4 - Installed
A7/W13 - Installed
A6/W12 - Removed
A5 /W 11 - Removed
A4jWIO - Removed
A3jW9 - Removed

* Vector Address (264 8 )
V2jWI - Installed
V3jW2 - Installed
V4jW3 - Removed
V5jW4 - Installed
V6jW5 - Removed
V7 jW6 - Installed
V8jW7 - Removed

*Standard

2-10

7408-6

Figure 2-7 Flexible Diskette Insertion

Do not touch the disk surface exposed in the diskette slot or index hole.

Do not clean the disk in any manner.

Keep the diskette away from magnets or tools that may have become magnetized. Any disk exposed to a
magnetic field may lose information.

Do not expose the diskette to a heat source or sunlight.

Always return the diskette to the envelope supplied with it to protect the disk from dust and dirt.
Diskettes not being used should be stored in the me box if possible.

When the diskette is in use, protect the empty envelope from liquids, dust, and metallic materials.

10.

Do not place heavy items on the diskette.

11.

Do not store diskettes on top of computer cabinets or in places where dirt can be blown by fans into the
diskette interior.

12.

If a diskette has been exposed to temperatures outside of the operating range, allow 5 minutes for ,
thermal stabilization before use. The diskette should be removed from its packaging during this time.

2-11

2.5.3 Diskette Storage
2.5.3.1 Short Term (Available for Immediate Use)
1.

Store diskettes in their envelopes.

Store horizontally, in piles of ten or less. If vertical storage is necessary, the diskettes should be
supported so that they do not lean or sag, but should not be subjected to compressive forces. Permanent
deformation may result from improper storage.

Store in an environment similar to that of the operating system; at a minimum, store within the
operating environment range.

2.5.3.2 Long Term - When diskettes do not need to be available for immediate use, they should be stored in their
original shipping containers within the nonoperating range of the media.
2.5.4 Shipping Diskettes
Data recorded on disks may be degraded by exposure to any sort of small magnet brought into close contact with
the disk surface. If diskettes are to be shipped in the cargo hold of an aircraft, take precautions against possible
exposure to magnetic sources. Because physical separation from the magnetic source is the best protection against
accidental erasure of a diskette, diskettes should be packed at least 3 in. within the outer box. This separation should
be adequate to protect against any magnetic sources likely to be encountered during transportation, making it
generally unnecessary to ship diskettes in specially shielded boxes.
When shipping, be sure to label the package:
DO NOT EXPOSE TO PROLONGED HEAT OR SUNLIGHT.
When received, the carton should be examined for damage. Deformation of the carton should alert the receiver to
possible damage of the diskette. The carton should be retained, if it is intact, for storage of the diskette or for future
shipping.

2-12

CHAPTER 3
RXll INTERFACE
PROGRAMMING INFORMATION
This chapter describes device registers, register and vector address assignments, programming specifications, and
programming examples for the RXll interface.
All software control of the RXll is performed by means of two device registers: the RXll Command and Status
register (RXCS) and a multipurpose RX 11 Data Buffer register (RXDB). These registers have been assigned bus
addresses and can be read or loaded, with certain exceptions, using any instruction referring to their addresses.
The RX01, which includes the mechanical drive (s), read/write electronics, and pCPU controller, contains all the
control circuitry required for implied seeks, automatic head position verification, and calculation and verification of
the CRC; it has a buffer large enough to hold one full sector of diskette data (128 8-bit bytes). Information is
serially passed between the interface and the RXOI.
A typical diskette write sequence, which is initiated by a user program, would occur in two steps:

Fill Buffer - A command to fill the buffer is moved into the RXCS. The Go bit (paragraph 3.2.1) must
be set. The program tests for Transfer Request (TR). When TR is detected, the program moves the first
of 128 bytes of data to the RXDB. TR goes false while the byte is moved into the RXOI. The program
retests TR and moves another byte of data when TR is true. When the RXOI sector buffer is full, the
Done bit will set, and an interrupt will occur if the program has enabled interrupts.

Write Sector - A command to write the contents of the buffer onto the disk is issued to the RXCS.
Again the Go bit must be set. The program tests TR, and when TR is true, the program moves the
desired sector address to the RXDB. TR goes false while the RXOI handles the sector address. The
program again waits for TR and moves the desired track address to the RXDB, and again TR is negated.
The RXOI locates the desired track and sector, verifies its location, and writes the contents of the sector
buffer onto the diskette. When this is done, an interrupt will occur if the program has enabled interrupts.

A typical diskette read occurs in just the reverse way: first locating and reading a sector into the buffer (Read
Sector) and then unloading the buffer into core (Empty Buffer). In either case, the content of the buffer is not valid
if Power Fail or Initialize follows a Fill Buffer or Read Sector function.
3.1 REGISTER AND VECTOR ADDRESSES
The RXCS register is normally assigned Unibus address 177170, and the RXDB register is assigned Unibus address
177172. The normal BR priority level is 5, but it can be changed by insertion of a different priority plug located on
the interface module. The vector address is 264.

3-1

3.2 REGISTER DESCRIPTION
3.2.1

RXCS - Command and Status (177170)

Loading this register while the RXOI is not busy and with bit 0 = 1 will initiate a function as described below and
indicated in Figure 3-1. Bits 0-4 write-only bits.

I
ERROR

I
TR

RX
INIT

FUNCTION

DONE

[

NOT USED

UNIT
SEL

INT
ENS

CP-1509

Figure 3-1 RXCS Format (RXll)

Bit No.

Description

Go - Initiates a command to RXOI. This is a write-only bit.

1-3

Function Select - These bits code one of the eight possible functions described in Paragraph
3.3 and listed below. These are write-only bits.
Code

Function
Fill Buffer
Empty Buffer
Write Sector
Read Sector
Not used
Read Status
Write Deleted Data Sector
Read Error Register

000
001
010
011
100
101
110
111

Unit select - This bit selects one of the two possible disks for execution of the desired
function. This is a write-only bit. Unit 0 is physically the left-hand unit in the rack.

Done -- This bit indicates the completion of a function. Done will generate an interrupt
when asserted if Interrupt Enable (RXCS bit 6) is set. This is a read-only bit.

Interrupt Enable - This bit is set by the program to enable an interrupt when the RXOI has
completed an operation (Done). The condition of this bit is normally determined at the time
a function is initiated. This bit is cleared by Initialize and is a read/write bit.

Transfer Request - This bit signifies that the RXll needs data or has data available. This is a
read-only bit.

8-13

Unused

3-2

Bit No.

Description
RX11 Initialize - This bit is set by the program to initialize the RX11 without initializing all
of the devices on the Unibus. This is a write-only bit.

CAUTION
Loading the lower byte of the RXCS will also load the upper
byte of the RXCS.
Upon setting this bit in the RXCS, the RXll will negate Done and move the head position
mechanism of drive 1 (if two are available) to track O. Upon completion of a successful
Initialize, the RX01 will zero the Error and Status register, set Initialize Done, and set RXES
bit 7 (DRY RDY) if unit 0 is ready. It will also read sector 1 of track 1 on drive O.
15

Error - This bit is set by the RX01 to indicate that an error has occurred during an attempt
to execute a command. This read-only bit is cleared by the initiation of a new command or
an Initialize (paragraph 3.6).

3.2.2 RXDB - Data Buffer Register (177172)
This register serves as a general purpose data path between the RXOI and the interface. It may represent one of four
RXOI registers according to the protocol of the function in progress (paragraph 3.3).
This register is read/write if the RXOI is not in the process of executing a command; that is, it may be manipulated
without affecting the RXOI subsystem. If the RX01 is actively executing a command, this register will only accept
data if RXCS bit 7 (TR) is set. In addition, valid data can only be read when TR is set.
CAUTION
Violation of protocol in manipulation of this register may
cause permanent data loss.
3.2.2.1 RXTA - RX Track Address (Figure 3-2) - This register is loaded to indicate on which of the 115 8 tracks a
given function is to operate. It can be addressed only under the protocol of the function in progress (paragraph 3.3).
Bits 8 through 15 are unused and are ignored by the control.

....

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

0- 114 8

NOT USED

CP-1510

Figure 3-2 RXTA Format (RX11)
3.2.2.2 RXSA - RX Sector Address (Figure 3-3) - This register is loaded to indicate on which of the 328 sectors a
given function is to operate. It can be addressed only under the protocol of the function in progress (paragraph 3.3).
Bits 8 through 15 are unused and are ignored by the control.
15

0
1-32 8

NOT USED

CP-151l

Figure 3-3 RXSA Format (RXll)
3-3

3.2.2.3 RXDB - RX Data Buffer (Figure 3-4) - All information transferred to and from the floppy media passes
through this register and is addressable only under the protocol of the function in progress (paragraph 3.3).

NOT USED
CP-1512

Figure 34 RXDB Format (RXll)
3.2.2.4 RXES - RX Error and Status (Figure 3-5) - This register contains the current error and status conditions
of the drive selected by bit 4 (Unit Select) of the RXCS. 'This read-only register can be addressed only under the
protocol of the function in progress (paragraph 3.3). The RXES is located in the RXDB upon completion of a
function.

IDRV
ROY

NOT USED

PAR I CRC

NOT USED
CP -1513

Figure 3-5 RXES Format (RX11)
RXES bit assignments are:
Bit No.

Description
CRC Error - A cyclic redundancy check error was detected as information was retrieved
from a data field of the diskette. 'The RXES is moved to the RXDB, and Error and Done are
asserted.
Parity Error - A parity error was detected on command or address information being
transferred to the RXOI from the Unibus interface. A parity error indication means that
there is a problem in the interface cable between the RXOI and the interface. Upon
detection of a parity error, the current function is terminated; the RXES is moved to the
RXDB, and Error and Done are asserted.

Initialize Done - This bit is asserted in the RXES to indicate completion of the Initialize
routine which can be caused by RXOI power failure, system power failure, or programmable
or Unibus Initialize.

3-5

Unused

Deleted Data Detected - During data recovery, the identification mark preceding the data
field was decoded as a deleted data mark (paragraph 1.3.3).

Bit No.

Description
Drive Ready - This bit is asserted if the unit currently selected exists, is properly supplied
with power, has a diskette installed correctly, has its door closed, and has a diskette up to
speed.
NOTE 1
The Drive Ready bit is only valid when retrieved via a Read
Status function or at completion of Initialize when it indicates
status of drive O.
NOTE 2
If the Error bit was set in the RXCS but Error bits are not set
in the RXES, then specific error conditions can be accessed via
a Read Error Register function (Paragraph 3.3.7).

3.3 FUNCTION CODES
Following the strict protocol of the individual function, data storage and recovery on the RX11 occur with careful
manipulation of the RXCS and RXDB registers. The penalty for violation of protocol can be permanent data loss.
A summary of the function codes is presented below:
000
001
010
011
100
101
110
111

Fill Buffer
Empty Buffer
Write Sector
Read Sector
Not used
Read Status
Write Deleted Data Sector
Read Error Register

The following paragraphs describe in detail the programming protocol associated with each function encoded and
written into RXCS bits 1-3 if Done is set.
3.3.1

Fill Buffer (000)

This function is used to fill the RX01 buffer with 128 8-bit bytes of data from the host processor. Fill Buffer is a
complete function in itself; the function ends when the buffer has been filled. The contents of the buffer can be
written onto the diskette by means of a subsequent Write Sector function, or the contents can be returned to the
host processor by an Empty Buffer function.
RXCS bit 4 (Unit Select) does not affect this function, since no diskette drive is involved. When the command has
been loaded, RXCS bit 5 (Done) is negated. When the TR bit is asserted, the first byte of the data may be loaded
into the data buffer. The same TR cycle will occur as each byte of data is loaded. The RX01 counts the bytes
transferred; it will not accept less than 128 bytes and will ignore those in excess. Any read of the RXDB during the
cycle of 128 transfers is ignored by the RX 11.
3.3.2 Empty Buffer (001)
This function is used to empty the internal buffer of the 128 data bytes loaded from a previous Read Sector or Fill
Buffer command. This function will ignore RXCS bit 4 (Unit Select) and negate Done.

3-5

When TR sets, the program may unload the first of 128 data bytes from the RXDB. Then the RXll again negates
TR. When TR resets, the second byte of data may be unloaded from the RXDB, which again negates TR. Alternate
checks on TR and data transfers from the RXDB continue until 128 bytes of data have been moved from the RXDB.
Done sets, ending the operation and initiating an interrupt if RXCS bit 6 (Interrupt Enable) is set.
NOTE
The Empty Buffer function does not destroy the contents of
the sector buffer.
3.3.3 Write Sector (010)
This function is used to locate a desired track and sector and write the sector with the contents of the internal sector
buffer. The initiation of this function clears bits 0, 1, and 6 of RXES (CRC Error, Parity Error, and Deleted Data
Detected) and negates Done.
When TR is asserted, the program must move the desired sector address into the RXDB, which will negate TR. When
TR is again asserted, the program must load the desired track address into the RXDB, which will negate TR. If the
desired track is not found, the RXII will abort the operation, move the contents of the RXES to the RXDB, set
RXCS bit 15 (Error), assert Done, and initiate an interrupt if RXCS bit 6 (Interrupt Enable) is set.
TR will remain negated while the RXOI attempts to locate the desired sector. If the RXOI is unable to locate the
desired sector within two diskette revolutions, the RXll will abort the operation, move the contents of the RXES
to the RXDB, set RXCS bit 15 (Error), assert Done, and initiate an interrupt if RXCS bit 6 (Interrupt Enable) is set.
If the desired sector is successfully located, the RXl1 will write the 128 bytes stored in the internal buffer followed
by a 16-bit CRC character that is automatically calculated by the RXOI. The RXll ends the function by asserting
Done and initiating an interrupt if RXCS bit 6 (Interrupt Enable) is set.
NOTE 1
The contents of the sector buffer are not valid data after a
power loss has been detected by the RXOI. The Write Sector
function, however, will be accepted as a valid function, and
the random contents of the buffer will be written, followed by
a valid CRC.
NOTE 2
The Write Sector function does not destroy the contents of
the sector buffer.
3.3.4 Read Sector (011)
This function is used to locate a desired track and sector and transfer the contents of the data field to the pCPU
controller sector buffer. The initiation of this function clears bits 0, 1, and 6 of RXES (CRC Error, Parity Error,
Deleted Data Detected) and negates Done.
When TR is asserted, the program must load the desired sector address into the RXDB, which will negate TR. When
TR is again asserted, the program must load the desired track address into the RXDB, which will negate TR.
If the desired track is not found, the RXII will abort the operation, move the contents of the RXES to the RXDB,
set RXCS bit 15 (Error), assert Done, and initiate an interrupt if RXCS bit 6 (Interrupt Enable) is set.

3-6

TR and Done will remain negated while the RXOI attempts to locate the desired track and sector. If the RXOI is
unable to locate the desired sector within two diskette revolutions after locating the presumably correct track, the
RXll will abort the operation, move the contents of the RXES to the RXDB, set RXCS bit 15 (Error), assert Done,
and initiate an interrupt if RXCS bit 6 (Interrupt Enable) is set.
If the desired sector is successfully located, the control will attempt to locate a standard data address mark or a
deleted data address mark. If either mark is properly located, the control will read data from the sector into the
sector buffer.
If the deleted data address mark was detected, the control will assert RXES bit 6 (DD). As data enters the sector
buffer, a CRC is computed, based on the data field and CRC bytes previously recorded. A non-zero residue indicates
that a read error has occurred. The control sets RXES bit 0 (CRC Error) and RXCS bit 15 (Error). The RXll ends
the operation by moving the contents of the RXES to the RXDB, sets Done, and initiates an interrupt if RXCS bit 6
(Interrupt Enable) is set.
3.3.5 Read Status (101)
The RXll will negate RXCS bit 5 (Done) and begin to assemble the current contents of the RXES into the RXDB.
RXES bit 7 (Drive Ready) will reflect the status of the drive selected by RXCS bit 4 (Unit Select) at the time the
function was given. All other RXES bits will reflect the conditions created by the last command. RXES may be
sampled when RXCS bit 5 (Done) is again asserted. An interrupt will occur if RXCS bit 6 (Interrupt Enable) is set.
RXES bits are defined in Paragraph 3.2.2.
NOTE
The average time for this function is 250 ms. Excessive use of
this function will result in substantially reduced throughput.
3.3.6 Write Sector with Deleted Data (110)
This operation is identical to function 010 (Write Sector) with the exception that a deleted data address mark
precedes the data field instead of a standard data address mark (paragraph 1.3.3.2).
3.3.7 Read Error Register Function (III)
The Read Error Register function can be used to retrieve explicit error information provided by the pCPU controller
upon detection of the general error bit. The function is initiated, and bits 0-6 of the RXES are cleared. Out is
asserted and Done is negated. The controller then generates the appropriate number of shift pulses to transfer the
specific error code to the Interface register and completes the function by asserting Done. The Interface register can
now be read and the error code interrogated to determine the type of failure that occurred (paragraph 3.6).
NOTE
Care should be exercised in use of this function since, under
certain conditions, erroneous error information may result
(Paragraph 3.5).
3.3.8 Power Fail
There is no actual function code associated with Power Fail. When the RXOI senses a loss of power, it will unload
the head and abort all controller action. All status signals are invalid while power is low.
When the RXOI senses the return of power, it will remove Done and begin a sequence to:
1.

Move drive 1 head position mechanism to track O.

Clear any active error bits.

3-7

Read sector I of track I of drive 0 into the sector buffer.

Set RXES bit 02 (Initialize Done) (Paragraph 3.2.2.4) after which Done is again asserted.

Set Drive Ready of the RXES according to the status of drive O.

There is no guarantee that information being written at the time of a power failure will be retrievable. However, all
other information on the diskette will remain unaltered.
A method of aborting a function is through the use of RXCS bit 14 (RX 11 Initialize). Another method is through
the use of the system Initialize signal that is generated by the PDP· 1 I RESET instruction, the console START key,
or system power failure.

3.4 PROGRAMMING EXAMPLES
3.4.1

Read Data/Write Data

Figure 3·6 presents a program for implementing a Write, Write Deleted Data, or a Read function, depending on the
function code that is used. The first instructions set up the error retry counters, PTRY, CTRY, and STRY. The
instruction RETRY moves the command word for a Write, Write Deleted Data, or Read into the RXCS.
The set of three instructions beginning at the label I $ moves the sector address to the RX 11 after Transfer Request
(TR) , which is bit 7, has been set. The three instructions beginning at the label 2$ move the track address to the
RXII after TR has been set. The group of instructions beginning at the label 3$ looks for the Done flag to set and
checks for errors.
An error condition, indicated by bit 15 setting, is checked beginning at ERFLAG. If bit 0 is set, a CRC error h::ts
occurred, and a branch is made to CRCER. If bit 1 is set, a parity error has occurred, and a branch is made to
PARER. If neither of the above bits is set, a seek error is assumed to have occurred and a branch is made to
SEEKER, where the system is initialized. In the case of a Write function, the sector buffer is refilled by a JMP to
FILLBUF. In the case of a Read function, a JMP is made to EMPBUFF.
In each of the PAR, CRC, and SEEK routines, the command sequence is retried ten times by decrementing the
respective retry counter. If an error persists after ten tries, it is a hard error. The retry counters can be set up to retry
as many times as desired.
NOTE
A Fill Buffer function is performed before a Write function,
and an Empty Buffer function is performed after a Read
function.
3.4.2 Empty Buffer Function
Figure 3·7 shows a program for implementing an Empty Buffer function. The first instruction sets the number of
error retries to ten. The address of the memory buffer is placed in register RO, and the Empty Buffer command is
placed in the RXCS. Existence of a parity error is checked starting at instruction 3 $. If a parity error is detected, the
Empty Buffer command is loaded again. If an error persists for ten retries, the error is considered hard.

3·8

1
2

.... IS
I PROGAAMM I NG EXAMPLES rOR THE R)(l1/I1X'l 'I.[X IILE DISI(E;TTE

I THE '01.1.01011 Ne IS THE RXll IUNDAAO DEV I CE AODRESS AND VECTOR ADOIIUS

1771711
177172
177172
177172
177172

6
7

8
9
1 III

RXCS-1771711
RXOI-177172
RlIS"177172
RXU-177172
RX[51177172

11
12
13
14
15
16
17
18
19
2 III
21
22
23
24
25
26
27
28
29
31il
31
32

33
34
35
36
37
38
39
4111
41
42
43
44
45
46
47
48
49
5111
51
52
54
55
56
57
58
59
6fl
61
62
63
64
65
66
67
68
69
70
71
72

: ~~E W~~~~?W ~~~ Ti S D~I.~~~;R~:;! ~G O~lI:~:~E A~' 1~~~0~R2~2C~.H~E~~~~~~TI or PROGIWI
Iio0CATION lECTOR) 01'" TRACI( "T" (THE CDNTENTS or PIIOGRA" 1.0CATlON TRACIC)
I

IIIUIilU
ilIIlUII6
1111011114

012767
2112767
11112767

177170
177770
17777'J

I11III11132111
1II1111l314
0111131111

'-11.

:
I

~=~I :tT:~T~~U~~~:TER
StEIC RETRY COUNTER

I WR I TE. "'A I TE DEI.ETEO OA TA. OR RUI)
I BITS 4 THRU 1 0' PROGRAM 1.0CAT I ON COMMANO !'JONU I N THE 'UNCTI ON

I BIT 4 • 1 MEANS UNIT 1 ( • II MUNI UNIT
I

I BITS 3 THRU 1 II THE COMMAND ( 4 • "'RITE. 1.4 • "'''ITt DEI.ETED DATA. 6 • IIUD)
I

1il1ll0lll22

"16767

J(l0;s06

17714111

RETRY I

MOV COMMAND. RICCS

I UNIT. (WRITE. W"ITE DEI.ETtD DATA. OR RUD)

; lolA I T F'OR THE TRANSI'"EH REQUEST 'IoAIi THEN TIIAN5F'ER THE lECTOR ADDIIElS
I

0l!l1II1I3111
I<11111i111134
02l1li11136

lS:

105767
001'"
116767

TSTB RlICS
BEQ 11
HOVB SECTOR, RICSA

177126

I
I WA I T F'OR

00I11III44
0111I11III5111
00I11III52

105767
1Il01'"
116767

I
21 :

177121il

THE TRANSI'"EH REQUEST "I.AIi THEN TRAIIS"ER THE TRACM ADDRUI

T5TB RXCS
BEQ
MDVB TRACI(. RXTA

I THE SECTOR AND TRACt< ADDRESsES io4AVE
I

I WSA I T 'OR THE DoNE F'I.AG AND

C~ECI(

I[E:~

TRANS'ERRED TO THE RXIl

F'OR ANY EtlRoRS

III'" THE rUNCTloN HAS CoMPI.ETED SuCCESS'UI.I. Y I No ER"OR rI.AG) THEN HAl. T
I

i<1IllIIIII 6 III
0111111166
00.,117111
oIillil 74
0111111176

032767
Cllil17H
01!15767
01il lIHl 1
o1/1 Iil" 0 111

31 I

alT IIIDoN£SIT. RXCS
8EC! 31
TST RXCS
liNE ERrLAG
HAl. T
I THE ERROR 'LAG IS sn

177074

~UT U~~~1. T~~E: °8~~E'~~:G lETS
TEST I'"OR TIjE ERROR "LAG
; INE I r AN ERROR HAS OCCUIIEO
01( • COM"I.ETEO

I THE CONTENTS oF' THE RkES IS THE E"ROR STATUI
; IF' THE RX[S BITS 1 AND II •
IIF' THE RXES BIT III • 1 THEN
III'" THE RXES BIT 1 • 1 THEN
0IIl1il111111
1il1l11l1l6
III 3011 III
1il1l0116

1il32767
01111414
12'32767
001404

0AIil1ll03

177164

001il0"2

17'1154

THtN SOME TY"E OF' SEEI( ERROR DCCURED
CRC £R"OIl HAl OCCUREO
"A" I TY EIIROR HAS OCCURED

~RF'I.AC I BIT 1113. RXES

aEC! SEEK
BIT 1112. RlIE9
aEa CRC

TEST rOR CIIC AND PAR I TV ERIIORS
NOT A "ARITY 0" CRC CMUSTJ IE A IEEI(
TEST "OR PARITy ERIIO"
NOT' "ARIlY ERROR CMUIT~ IE A C"C

FlAR I TV ERROR HAS OCCURED

IINCREME~T
I

AND TEST THE "A"ITY tllRo" RETIIY COUNTER PROGRAM 1.0CATION " PTIIY "

I AND RETRY THE" COMMANO " UNTIl. THE "ARITY ERROR "ECOYERS
I

I OR UNT II. THE "TRY COUNTER OVE"'1.0WS To
I

IIIU1211l
UIIl124
ilIIll126

"0'267
001336
ilIII0IIl0111

INC pTRY
liNE RETRY
HAl. T

JI!0202

III:T"Y THE: CO"lMAND
Io4UD PAR lTV EIlROR

I A CRC ERROR HAS oCCUHEO
I

IINCREMENT AND TEST THE CRC ERROR IIETRV COUNTER PRoCRAM LOCATioN" CT"" "
I

I AND RrTRY THE COMMAND UNT II. THE CIIC EIIRO" RtCOVERI
I

lOR UNT II. THE CTRY COUNTER OVEllrI.O""
1il1il1ll13111
"U134
0U136

U'267
<101332
I""0 III 0 III

CRC I

INC CT"Y
BN!: RETRY
Io4AL T
I THE ERROR rLAG I S SET

0"1il174

I THE ERROR IS CNoT] A PARITY ERRoR

93
94
95
96
97
98
99
10111

"IOV 111-11. pTAY
MOV 111-111. CTRY
MOV
STRY

8111
81
82
83
84
85
86
87
88
89
91
92

START I

73
74
75
76
77
78
79

COMMAND STATUS REGISTER
DAU IurrEIi REG lITER
SECTOR AODIltSS REGISTU
TRACM ADORESS RtOlSTER
tRIIDII IUTUS REGISTER

IIETRV THE OOM"IANI)

It!AO C"C ERROR
A~D

II CNOT] A CRC ER"OR

I THERErORE I T MUST BE , SEEI( ERROR
I

I (STATE or RlICS II TS Il AND 1 AIU .)
I

l11l1I11114111

012767

041il00"

177122

SEEI(:

"IOV IIIINIT. RXCS

INITIAI.IIE

UJ1

; INCREMENT AND TEIIT THE SEEI( ERROR RET"Y COUNTER PRoGRA" 1.0CATION "

102

lIi!I3

; AND REny THE COMMAND UNTI I. THE SEEIC ERIIOR "ECoVERI

1'"
105
11il6
1117
1118
a9

I OR UNT II. THE CTRY COUNTER OVER"I.DW, To •
I

ilIIIIII146
UIII152
0IIl1ll154

l11l1I'267
1111111323
2l1li 11111 Iil III

0011116111

INC STRY
INE RETRY
HAl. T

"ETRY THE OOMMAND
Io4UD lEEI( ERRO"

Figure 3-6 RXll Write/Write Deleted Data/Read Example

3-9

Sf"" "

160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
18"
185
186
187
188
189
190
191
192
193
19"
195
196
197
198
199
20"

;THE rO~~OWING IS A PMOGRA~MINC EXAM~~E or P~OTOCO~ REQUIRED TO

IE~pTY

0U242
UII251
031254

2112767
.,12700
.,16767

206
207
208
209
211/1
211
212
213
21"
215
216
217
218
219
2UI

221
222
223
22"
225
226
227
228

229
230
231
232

SECTOR Burr~R or 12a a-SIT BYTES
8 TRVS TO EMPTV THE tECToR BurrER
OATA BurrER
ISSUE THE COMMANO

EENTRYI MOV '-10, pTRV
[SETUPI MOV 'BurrER, H"
MOV COMMAND, RXCS

~ROHCRAMS

;WAIT roR A TRANSPER REQUEST r~AC BErO~E TRANsrERRING OATA TO THE PROGRAMS

,DATA BurrER rRoN THE RX01 SECTOR Bur'ER

I lolA IT

roR A DONE rLAC TO INDICATE THE COMpLETioN 0' THE EM~TV BUrrER COMMAND

IPRIoR TO TESTIN G THE ERROR r~AG

UI262
000266
000271
0""276

t~OOPI

1"'767

0"U14

TSTB RXCS

TEST rOR T_ANsrER REQUEST 'LAG
.NE Ir TRA~S'ER REQUEST '~AG IS SET
TEIT rOR DONE '~'G
BEO UNTIL THt DONE rLAC lETS

tlMI t;MPTY

176672

2132767

lIT 'OONESIT, RXCS
BEQ E~OOP

001771

;THE DONE 'LAG IS SET

;TE5T roR ANY ERRORS
00111301
00111304
0"'306

iH,,767

(ON~Y

ERRoR poSSIB~£ IS A PARITY ERROR)

1ST RXCS
BNE 11
HALT

176664

0U0"1
"00"00
I

,INcrEMENT AND TEST THE PARITV ERROR RET_y P_OGRAM ~oCATloN " pTRV "

,AND RETRY THE COMMANC UNTI~ THE ERROR RECoVERS
I

lOR UNTIL THE PTRV CUNTER OVERr~oWS TO I

,
0U3U
a""314
<lIH'316

15:

"0'267
13013"
001!J1!100

INC PTRY
BNE tStTUP
HALT

RETRV TO EMPTY THE SECTOR BurrER
HARD PARITV ERROR

;THE TRANsrER REQUEST r~AG Is SET

ITRANsrER DATA TO THE PHOGRAM

201

2"2
203
20"

THE

177770
(1:'0342
kHl00,4

,
176646

00032"
000324

EMPTY I

DATA BUrrER rROM THE RXBl SECTO~ BurrER

~2V~L~~~B' '(H"'·

ITHE rO~~OWING 3 PROGHAM LOCATIONS ARE THE E_ROR RETRY COUNTERS
U"326
"""33"
"""332

iZI:1!0000
~2lU00

J300"0

l 'ARITY ERROR RETRY COUNTER
; CRC ER~OR ~ETRV COUNTER
l SEEK ERROR RETRY COUNTER

r'TRV:
CTRy:
STRV:

lPROGRAM ~OCATION " COMMAND" CONTAINS T~E COMMAND TO BE ISSUED VIA THE LCD lOT

;WRITE (4), WRITE OELETED DATA (14),
I

READ (6), OR EM~TY BurrER (2)

; 4, 14, 6,

0U334

COMMANDI

001336

SECTOR; m

OR 2 • (GO BIT 1 • 1)

IPROGRAM ~OCATION " SECTOR" CONTAINS THE SECTOR ADDRESS (1 TO 32 OCTA~)

1 TO 32 OCTAL

lPROGRAM ~OCATION " THACK " CONTAINS TWE TRACK ADDRESS (II TO 114 OCTA~)

TRACK I

"00341

l B TO 114 OCTA~

lPROGRAM EQUIVALENTS

,
O:1!U40
,,4U00
iZlU342
""0'42
00011101

DONEB I TIl 41
INIT-4U""
BurrER-,
,laurrER+~"1/l

,END

Figure 3-7 RXll Empty Buffer Example

3-10

If no error is indicated, the program looks for the Transfer Request (TR) flag to set. The Error flag is retested if TR
is not set. Once TR sets, a byte is moved from the RXll sector buffer to the core locations of BUFFER. The
process continues until the sector buffer is empty and the Done bit is set.
3.4.3 Fill Buffer Function
Figure 3-8 presents a program to implement a Fill Buffer function. It is very similar to the Empty Buffer example.
3.5 RESTRICTIONS AND PROGRAMMING PITF ALLS
A set of restrictions and programming pitfalls for the RXII is presented below.
1.

Depending on how much data handling is done by the program between sectors, the minimum interleave
of two sectors may be used, but to be safe a three-sector interleave is recommended.

If an error occurs and the program executes a Read Error Register function (111), a parity error may
occur for that command. The error status would not be for the error in which the Read Error Register
function was originally required.

The DRV SEL RDY bit is present only at the time of a Read Status function (101) for both drives, and
after an Initialize, depending on the status of drive O.

It is not required to load the Drive Select bit into the RXCS when the command is Fill Buffer (000) or
Empty Buffer (010).

Sector Addressing: 1-26 (No sector 0)
Track Addressing: 0-76

A power failure causing the recalibration of the drives will result in a Done condition, the same as
finishing reading a sector. However, during a power failure, RXES bit 2 (Initialize Done) will set.
Checking this bit will indicate a power fail condition.

Excessive usage of the Read Status function (101) will result in drastically decreased throughput,
because a Read Status function requires between one and two diskette revolutions or about 250 ms to
complete.

3.6 ERROR RECOVERY
There are two error indications given by the RXII system. The Read Status function (paragraph 3.3.5) will assemble
the current contents of the RXES (paragraph 3.2.2), which can be sampled to determine errors. The Read Error
Register function (paragraph 3.3.7) can also be used to retrieve explicit error information. The RXll Interface
register can be interrogated to determine the type of failure that occurred.
A list of error codes is presented on the following page.
NOTE
A Read Status function is not necessary if the DRV RDY bit is
not going to be interrogated, because the RXES is in the
Interface register at the completion of every function.

3-11

Octal
Code
0010
0020
0030

0040
0050

0060
0070
0110
0120

0130
0140
0150
0160
0170
0200
0210

Error Code Meaning
Drive 0 failed to see home on Initialize.
Drive 1 failed to see home on Initialize.
Found home when stepping out 10 tracks for INIT.
Tried to access a track greater than 77.
Home was found before desired track was reached.
Self-diagnostic error.
Desired sector could not be found after looking at 52 headers (2 revolutions).
More than 40 J1,S and no SEP clock seen.
A preamble could not be found.
Preamble found but no I/O mark found within allowable time span.
eRe error on what we thought was a header.
The header track address of a good header does not compare with the desired track.
Too many tries for an IDAM (identifies header).
Data AM not found in allotted time.
eRe error on reading the sector from the disk. No code appears in the ERREG.
All parity errors.

3·12

111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158

ITHE rO~~OWING 15 A PHOGRAMMING EXAM'~E or T~E PROTOCO~ REQUIRED TO
1
IrI~L

1
1

0""156
UIII164
UI17111

1:112767
012700
016767

177773
000342
030140

0119142
176772

THE SECTOR BurrtR WITH 128 a-SIT BVTES

NOTE: THE DATA To rlL~ T~E SECTOR BU,rER CAN BE ASSEMBLED IN CORE IN T~E
EVEN ADDRESSES BYTES or 128 WORDS OR IN BOT~ BYTES or 64 WORDS

rENTRY: MOV '~lll, PTRY
SETUPI MOV *BurrER, R0
MOV COMMAND, HXCS

• TRVS TO 'ILL T~E SECTOR Bu,rER
'AOORAMS DATA surrER
ISSUE THE COMMAND

:WAIT rOR A TRANsrER HEQUEST rLAG et'oRE TRANsrERRING DATA rRoM THE PROGRA~S

IDATA BurrER TO THE RXlIIl SECTOR BUrrER

,WAIT rOR A 00 Nt rLAT To INDICATE T~E COMPLETION 0' THE rILL 8u,rER COMMAND
1

IPRIOR To TESTING THE ERROR r~AO

01111176
UI202
U1204
001212

10'767
00H14
032767
1391771

LOOP'

176766
176"6

TEST rOR T~ANsrtR REQUEST '~AG
lEO rr TRANsrER REQUeST '~AG SET
TEST rOR T~E DONE '~AG
lEO UNTIL THE DONE r~AG SETS

TSTS Rxes
tlMl

0"0040

nl.,L

BIT 'DONEBIT, RXCS
BEQ LOOP

ITHE DONE rLAG IS SET

ITEST rOR ANY ERRORS

(ON~Y

ERROR POSSJ8~E Is A PARITY ERROR)

0U214
III 1!IB22 III
U'222

0,.",767
01111001
000""'0

TST RXCS
SNE 11
HALT

176750
1

IINCREMENT ANO TEST THE PARITY ERROR RETRY PROGRAM LOCATION" ,TRY"

IANO RETRY THE COMMANO UNTI~ THE ERROR RECOVERS
I

lOR UNTI~ T~E PTRY COUNTER OVER'LOWS To
1!IB0224
2'''023111
0011232

005267
001355
00EJ1!02'

000076

lS:

INC PTRY
BNE SETUP
HALT

RETRV TO riLL THE SECTOR BurrER
~ARD 'ARITV ERROR

ITHE TRANsrER REQUEST rLAG IS SET

ITRANsrER DATA rROM THE PROGRAMS OAT A BurrER TO THE RXll SECTOR BurrER
1

0011234
U'241

113067

oQIrIl 756

176732

rILL:

MOve '(Rm)., HXDB
SR LOOP

; 'ROGAA~S D4TA BurrER 15 64 WoRDS IN ~EN~TH

Figure 3-8 RXII Fill Buffer Example

3-13

CHAPTER 4
RX8E INTERFACE
PROGRAMMING INFORMATION
The RX8E interface allows two modes of data transfer: 8-bit word length and 12-bit word length. In the 12-bit
mode, 64 words are written in a diskette sector, thus requiring two sectors to store one page of information. The
diskette capacity in this mode is 128,128 12-bit words (1,001 pages). In the 8-bit transfer mode, 128 8-bit words
are written in each sector. Disk capacity is 256,256 8-bit words, which is a 33 percent increase in disk capacity over
the 12-bit mode. Eight-bit mode must be used for generating IBM-compatible diskettes, since 12-bit mode does not
fully pack the sectors with data. The hardware puts in the extra Os. Data transfer requests occur 23 J.,lS after the
previous request was serviced for 12-bit mode (18 J.,lS for 8-bit mode). There is no maximum time between the
transfer request from the RXOI and servicing of that request by the host processor. This allows the data transfer to
and from the RXOI to be interrupted without loss of data.
4.1 DEVICE CODES
The eight possible device codes that can be assigned to the interface are 70-77. These device codes define address
locations of a specific device and allow up to eight RX8E interfaces to be used on a single PDP-8. These multiple
device codes are also shared with other devices. Depending on what other devices are on the system, the RX8E
device code can be selected to avoid conflicts. (Refer to the PDP-8 Small Computer Handbook for specific device
codes.)
The device codes are selected by switches according to Table 4-1. These switches control AC bits 6-8, while AC bits
3-5 are fixed at 1s. The device code is initially selected to be 70. Switches 7 and 8 are not connected and will not
affect the device selection code. The switches are all located on a single DIP switch package that is located on the
M8357 RX8E interface board.
Table 4-1
Device Code Switch Selection
Device
Code
77
76
75
74
73
72
71
70

SI
0
0
0
0
1
1
1
1

S2
0
0
1
1
0
0
1
1

0
1
0
1
0
1
0
1

S4
1
1
1
1
0
0
0
0

S5
1
1
0
0
1
1
0
0

S6
1
0
1
0
1
0

1
0

4-1

o (OFF)
S7
X
X
X
X
X
X
X
X

S8
X
X
X
X
X
X
X
X

c::::::J
c:::J
c:::J
c::::J
r::::::::::J
r::::::::::J
r::::::::::J
c:::J

1 (ON)

Sl
S2
S3
S4

SS
S6
S7
S8

4.2 INSTRUCTION SET
The RX8E instruction set is listed below and described in the following paragraphs.
lOT

Mnemonic

67xO
67xl
67x2
67x3
67x4
67xS
67x6
67x7

Description
No Operation
Load Command, Clear AC
Transfer Data Register
Skip on Transfer Request Flag, Clear Flag
Skip on Error Flag, Clear Flag
Skip on Done Flag, Clear Flag
Enable or Disable Disk Interrupts
Initialize Controller and Interface

LCD
XDR
STR
SER
SDN
INTR
INIT

4.2.1 Load Command (LCD) - 67xl
This command transfers the contents of the AC to the Interface register and clears the AC. The RXOI begins to
execute the function specified in AC 8,9, and 10 on the drive specified by AC 7. A new function cannot be initiated
unless the RXOI has completed the previous function. The command word is defined as shown in Figure 4-1.
00

FUNCTION

NOT

USED
8/12

DRV

SEL

Figure 4-1

CP-l:l14

LCD Word Format (RX8E)

The command word is described in greater detail in Paragraph 4.3.1.
4.2.2 Transfer Data Register (XDR) - 67x2
With the Maintenance flip-flop cleared, this instruction operates as follows. A word is transferred between the AC
and the Interface register. The direction of the transfer is governed by the RX01, and the length of the word
transferred is governed by the mode selected (8-bit or 12-bit). When Done is negated, executing this instruction
indicates to the RXOI:
1.

That the last data word supplied by the RXOI has been accepted by the PDP-8, and the RXOI can
proceed, or

That the data or address word requested by the RXOI has been provided by the PDP-8, and the RXOI
can proceed.

A data transfer (XDR) from the AC always leaves the AC unchanged. If operation is in 8-bit mode, AC 0-3 are
transferred to the Interface register but are ignored by the RXOI. Transfers into the AC are 12-bit jam transfers
when in 12-bit mode. When in 8-bit mode, the 8-bit word is ORed into AC 4-11, and AC 0-3 remain unchanged.
When the RXOI is done, this instruction can be used to transfer the RXES status word from the Interface register to
the AC. The selected mode controls this transfer as indicated above.

4-2

4.2.3 STR - 67x3
This instruction causes the next instruction to be skipped if the Transfer Request (TR) flag has been ,set by RXOI
and clears the flag. The TR flag should be tested prior to transferring data or address words with the XDR
instruction to ensure the data or address has been received or transferred, or' after an LCD instruction to ensure the
command is ih the Interface register. In cases where an XDR follows an LCD, the TR flag needs to be tested only
once between the two instructions. (See programming example in Paragraph 4.5.1.)
4.2.4 SER - 67x4
This instruction causes the next instruction to be skipped if the Error flag has been set by an error condition in the
RXOI and clears the flag. An error also causes the Done flag to be set (paragraph 4.3.6).
4.2.5 SDN - 67x5
This instruction causes the next instruction to be skipped if the Done flag has been set by the RXOI indicating the
completion of a function or detection of an error condition. If the Done flag is set, it is cleared by the SDN
instruction. This flag will interrupt if interrupts are enabled.
4.2.6 INTR - 67x6
This instruction enables interrupts by the Done flag if AC 11 = 1. It disables interrupts if AC 11 = O.
4.2.7 INIT - 67x7
The instruction initializes the RXOI by moving the head position mechanism of drive 1 (if drive 1 is available) to
track O. It reads track 1, sector 1 of drive O. It zeros the Error and Status register and sets Done upon successful
completion of Initialize. Up to 1.8 seconds may elapse before the RXOI returns to the Done state. Initialize can be
generated programmably or by the Omnibus Initialize.
4.3 REGISTER DESCRIPTION
Only one physical register (the Interface register) exists in the RX8E, but it may represent one of the six RXOI
registers described in the following paragraphs, according to the protocol of the function in progress.
4.3.1 Command Register (Figure 4-2)
The command is loaded into the Interface register by the LCD instruction (paragraph 4.2.1).

FUNCTION

NOT

USED
8/12

DRV

SEL

Figure 4-2 Command Register Format (RX8E)

4-3

CP-HI14

The function codes (bits 8, 9, 10) are summarized below and described in Paragraph 4.4.
Code

Function

000
001
010
011
100
101
110
111

Fill Buffer
Empty Buffer
Write Sector
Read Sector
Not used
Read Status
Write Deleted Data Sector
Read Error Register

The DRV SEL bit (bit 7) selects one of the two drives upon which the function will be performed:
AC 7= 0
AC 7 = 1

Select drive 0
Select drive 1

The 8/12 bit (bit 5) selects the length of the data word.
AC 5 =0
AC 5 = 1

Twelve-bit mode selected
Eight-bit mode selected

The RX8E will initialize into 12-bit mode.
4.3.2 Error Code Register (Figure 4-3)
Specific error codes can be accessed by use of the Rear Error Register function (111) (paragraph 4.4.7). The specific
octal error codes are given in Paragraph 4.7.
00

____

~~~

______

~Il~

______________

NOT USED

~~~

ERROR

______________

CODE
CP-l~l~

Figure 4-3 Error Code Register Format
The Maintenance bit (M bit) can be used to diagnose the RX8E interface under off-line and on-line conditions. The
off-line condition exists when the BCOSL-IS cable is disconnected from the RXOI; the on-line condition exists when
the cable is connected to the RXOI.

If an LCD lOT (I/O Transfer) is issued with AC 4 = 1, the Maintenance flip-flop is set. When the Maintenance
flip-flop is set, the assertion of RUN on following XDR instructions is inhibited, and all data register transfers (XDR)
are forced into the AC. The Maintenance bit allows the Interface register to be written and read for maintenance
checks. The Maintenance flip-flop is cleared by Initialize or by an LCD lOT with AC 4 = O.
The following paragraphs describe more explicitly how to use the Maintenance bit in an off-line mode.
The contents of the interface buffer cannot be guaranteed immediately following the first LCD lOT, which sets the
Maintenance flip-flop. However, successive LCD lOTs will guarantee the contents of the Interface register. The
contents of the Interface register can then be verified by using the XDR lOT to transfer those contents into the AC.

4-4

In addition, the Maintenance flip-flop directly sets the Skip flags, which will remain set as long as the Maintenance
flip-flop is set. Skipping in these flags as long as the Maintenance flip-flop is set will not clear the flags. Setting and
then clearing the Maintenance flip-flop will leave the Skip flags in a set condition. The skip lOTs can then be issued
to determine whether or not a large portion of the interface skip logic is working correctly.
The Maintenance flip-flop can also be used to determine if the interface is capable of generating an interrupt on the
Omnibus. The Maintenance flip-flop is set, thus causing the Done flag to set. The Interrupt Enable flip-flop can be
set by issuing an INTR lOT with AC bit 11 = 1. The combination of Done and Interrupt Enable should generate an
interrupt.
The Maintenance flip-flop can also be used to test the INIT lOT. The Maintenance flip-flop is set and cleared to
generate the flags, and INIT lOT is then executed. If execution of INIT lOT is internally successful, all of the flags
and the Interrupt Enable flip-flop should be cleared if they were previously set.
In the on-line mode, use of the Maintenance bit should be restricted to writing and reading the Interface register.
The same procedure described to write and read the Interface register in the off-line mode should be implemented in
the on-line mode. Additional testing of the RX8E in the on-line mode should reference the appropriate circuit
schematics. Exiting from the on-line Maintenance bit mode should be finalized by an initialize to the RXO 1.
4.3.3 RXT A - RX Track Address (Figure 44)
This register is loaded to indicate on which of the 77 tracks a given function is to operate. It can be addressed only
under the protocol of the function in progress (paragraph 4.4). Bits 0 through 3 are unused and are ignored by the
control.

0- 114 8

NOT USED

CP-l~16

Figure 44 RXTA Format (RX8E)
4.3.4 RXSA - RX Sector Address (Figure 4-5)
This register is loaded to indicate on which of the 26 sectors a given function is to operate. It can b~ addressed only
under the protocol of the function in progress (Paragraph 4.4). Bits 0 through 3 are unused and are ignored by the
control.

.....
NOT USED

1- 32 8
CP-l~17

Figure 4-5 RXSA Format (RX8E)

4-5

4.3.5 RXDB - RX Data Buffer (Figure 4-6)
All information transferred to and from the floppy media passes through this register and is addressable only under
the protocol of the function in progress. The length of data transfer is either B or 12 bits, depending on the state of
bit 5 of the Command register when the LCD lOT is issued (paragraph 4.3.1).

12 Bl T
MODE ONLY

8 or 12 BIT
MODE
CP-l~18

Figure 4-6 RXDB Format (RXBE)

4.3.6 RX Error and Status (Figure 4-7)
The RXES contains the current error and status conditions of the selected drive. This read-only register can be
accessed by the Read Status function (101). The RXES is also available in the Interface register upon completion of
any function. The RXES is accessed by the XDR instruction. The meaning of the error bits is given below.

I
J

......---~

ORV
ROY

NOT USED

PAR

I I
eRe

NOT USED
CP-l~19

Figure 4-7 RXES Format (RXBE)
Bit No.

Description

CRC Error - The cyclic redundancy check at the end of the header or data field has
indicated an error. The header or data must be considered invalid; it is suggested that the
data transfer be retried up to ten times, as most data errors are recoverable (soft). (See
Chapter 6).

Parity Error - When status bit 10 = 1, a parity error has been detected on command and
address information being transferred to the RXOI pCPU controller from the RXBE
interface. Upon detection of a parity error, the current function is terminated, the RXES
status word is moved to the Interface register, and the Error and Done flags are set. The
function can be retried to determine if the parity error is a soft or hard error. A parity error
indication means that there is a problem in the interface cable between the RXOI and the
interface.

Initialize Done - This bit indicates completion of the Initialize routine. It can be asserted
due to RXOI power failure, system power failure, or programmable or bus Initialize. This bit
is not available within the RXES from a Read Status function.

4-6

Bit No.

Description

Deleted Data (DD) - In the course of reading data, a deleted data mark was detected in the
identification field. The data following will be collected and transferred normally, as the
deleted data mark has no further significance within the RXOl. Any alteration of fIles or
actual deletion of data due to this mark must be accomplished by user software. This bit will
be set if a successful or unsuccessful Write Deleted Data function is performed.

Drive Ready - This bit is asserted if the unit currently selected exists, is properly supplied
with power, has a diskette installed properly, has its door closed, and has a diskette up to
speed.
NOTE 1
This bit is only valid for either drive when retrieved via a Read
Status function or for drive 0 upon completion of an Initialize.
NOTE 2
If the Error bit was set in the RXCS but Error bits are not set
in the RXES, then specific error conditions can be accessed via
a Read Error Register function.

4.4 FUNCTION CODE DESCRIPTION
RX8E functions are initiated by means of the Load Command lOT (LCD). The Done flag should be tested and
cleared with the SDN instruction in order to verify that the RX8E is in the Done state prior to issuing the LCD
instruction. Upon receiving an LCD instruction while in the Done state, the RX8E enters the Not Done state while
the command is decoded. Each of the eight functions summarized below requires that a strict protocol be followed
for the successful transfer of data, status, and address information. The protocol for each function is described in the
following sections, and a summary table is presented below.

Octal

0
2
4
6
10
12
14
16

0
0
0
0

AC
9
0
0
1
1
0
0

Function

0
1
0

Fill Buffer
Empty Buffer
Write Sector
Read Sector
Not Used
Read Status
Write Deleted Data Sector
Read Error Register

1
0
1
0
1

NOTE
AC bit 11 is assumed to be 0 in the above octal codes, since
AC bit 11 can be 0 or 1.
4.4.1

Fill Buffer (000)

This function is used to load the RXOI sector buffer from the host processor with 64 12-bit words if in 12-bit mode
or 128 8-bit words if in 8-bit mode. This instruction only loads the sector buffer. In order to complete the transfer
to the diskette, another function, Write Sector, must be performed. The buffer may also be read back by means of
the Empty Buffer function in order to verify the data.

4-7

Upon decoding the Fill Buffer function, the RXOI will set the Transfer Request (TR) flag, signaling a request for the
first data word. The TR flag must be tested and cleared by the host processor with the STR instructions prior to
each successive XDR lOT (paragraph 4.2.3). The data word can then be transferred to the Interface register by
means of the XDR lOT. The RXOI next moves the data wO,rd from the Interface register to the sector buffer and
sets the TR flag as a request for the next data word. The sequence above is repeated until the sector buffer has been
loaded (64 data transfers for 12-bit mode or 128 data transfers for 8-bit mode). After the 64th (or 128th) word has
been loaded into the sector buffer, the RXES is moved to the Interface register, and the RXOI sets the Done flag to
indicate the completion of the function. It is, therefore, unnecessary for the host processor to keep a count of the
data transfers. Any XDR commands after Done is set will result in the RXES status word being loaded in the AC.
The sector buffer must be completely loaded before the RX8E will set Done and recognize a new command. An
interrupt would now occur if Interrupt Enable were set.
4.4.2 Empty Buffer (001)
This function moves the contents of the sector buffer to the host processor. Upon decoding this function, RXES bits
10 and 11 (Parity Error and CRC Error) are cleared, and the TR flag is set with the first data word in the Interface
register. This TR flag signifies the request for a data transfer from the RX8E to the host processor. The flag must be
tested and cleared, then the word can be moved to the AC by an XDR command. The direction of the transfer for
an XDR command is controlled by the RXOI. The TR flag is set again with the next word in the Interface register.
The above sequence is repeated until 64 words (128 bytes if 8-bit mode) have been transferred, thus emptying the
sector buffer. The Done flag is then set after the RXES is moved in the Interface register to indicate the end of the
function. An interrupt would now occur if Interrupt Enable were set.

NOTE
The Empty Buffer function does not destroy the contents of
the sector buffer.
4.4.3 Write Sector (010)
This function transfers the contents of the sector buffer to a specific track and sector on the diskette. Upon
decoding this function, the RX8E clears bits 10 and II (parity Error and CRC Error) of the RXES and sets the TR
flag, signifying a request for the sector address. The TR flag must be tested and cleared before the binary sector
address can be loaded into the Interface register by means of the XDR command. The sector address must be within
the limits 1-32 8 .
The TR flag is set, signifying a request for the track address. The TR flag must be tested and cleared, then the binary
track address may be loaded into the Interface register by means of the XDR command. The track address must be
within the limits 0-1148.
The RXOI tests the supplied track address to determine if it is within the allowable limits. If it is not, the RXES is
moved to the Interface register, the Error and Done flags are set, and the function is terminated.
If the track address is legal, the RXOI moves the head of the selected drive to the selected track, locates the
requested sector, transfers the contents of the sector buffer and a CRC character to that sector, and sets Done. Any
errors encountered in the seek operation will cause the function to cease, the RXES to be loaded into the Interface
register, and the Error and Done flags to be set. If no errors are encountered, the RXES is loaded into the Interface
register and only the Done flag is set.

NOTE
The Write Sector function does not destroy the contents of
the sector buffer.

4-8

4.4.4 Read Sector (011)
This function moves a sector of data from a specified track and sector to the sector buffer. Upon decoding this
function, the RX8E clears RXES bits 5, 10, 11 (Deleted Data, Parity Error, CRC Error) and sets the TR flag,
signifying the request for the sector address. The flag must be tested and cleared. The sector address is then loaded
into the Interface register by means of the XDR command. The TR flag is set, signifying a request for the track
address. The flag is tested and cleared by the host processor, and the track address is then loaded into the Interface
register by an XDR command. The legality of the track address is checked by the RXOI. If illegal, the Error and
Done flags are set with the RXES moved to the Interface register, and the function is terminated. Otherwise, the
RXOI moves the head to the specified track, locates the specified sector, transfers the data to the sector buffer,
computes and checks CRC for the data. If no errors occur, the Done flag is set with the RXES in the Interface
register. If an error occurs anytime during the execution of the function, the function is terminated by setting the
Error and Done flags with RXES in the Interface register. A detection of CRC error results in RXES bit 11 being set.
If a deleted data mark was encountered at the beginning of the desired data field, RXES bit 5 is set.
4.4.5 Read Status (l 01)
Upon decoding this function, the RXOI moves the RXES to the RX8E Interface register and sets the Done flag. The
RXES can then be read by the Transfer Data Register command (XDR). The bits are defined in Paragraph 4.3.6.
NOTE
The average time for this function is 250 ms. Excessive use of
this function will result in substantially reduced throughput.
4.4.6 Write Deleted Data Sector (110)
This function is identical to the Write Data function except that a deleted data mark is written prior to the data field
rather than the normal data mark (Paragraph 1.3.3.2). RXES bit 5 (Deleted Data) will be set in the RX8E Interface
register upon completion of the function.
4.4.7 Read Error Register Function (111)
The Read Error Register function can be used to retrieve explicit error information upon detection of the Error flag.
Upon receiving this function, the RXOI moves an error code to the Interface register and sets Done. The Interface
register can then be read via an XDR command and the code interrogated to determine which type of failure
occurred (paragraph 4.7).
NOTE
Care should be exercised in use of this function because, under
certain conditions, erroneous error information may result
(Paragraph 4.6).
4.4.8 Power Fail
There is no actual function code associated with Power Fail. When the RXOI senses a loss of power, it will unload
the head and abort all controller action. All status signals are invalid while power is low.
When the RXOI senses the return of power, it will remove Done and begin a sequence to:
1.

Move drive 1 head position mechanism to track O.

Clear any active error bits.

Read sector 1 of track 1 of drive o.

Set Initialize Done bit of the RXES, after which Done is again asserted.

4-9

There is no guarantee that information being written at the time of a power failure will be retrievable. However, all
other information on the diskette will remain unaltered.
A method of aborting an incomplete function is with the INIT lOT (paragraph 4.2.7).
4.5 PROGRAMMING EXAMPLES
4.5.1 Write/Write Deleted Data/Read Functions
Figure 4-8 presents a program for implementing a Write, Write Deleted Data, or a Read function with interrupts
turned off (10 F). The first three steps preset the PTRY, CTRY, and STRY retry counters, which are set at ten
retries but can be changed to any number. Starting at RETRY, the program tests for 8- or 12-bit mode, type of
function, and drive. Once the command is loaded, the program waits in a loop for the controller to respond with
Transfer Request (TR). When TR is set, the sector address is loaded and the AC is cleared. The program loops while
waiting for the controller to respond with another TR. When TR is reset, the track address is loaded, and the AC is
cleared again. The program loops to wait for the Done condition.
When the Done flag is set, the program checks for an error condition, indicated by the Error flag being set. If the
AC = 0000, then the error is a seek error; if bit 10 of the AC is set, the error is a parity error; and if bit 11 of the AC
is set, the error is a CRC error. Error status from the RXES is saved and tested to determine the error (paragraph
4.3.6). The RXES will not include the Select Drive Ready bit. If a parity error is detected, the program increments
and tests the PTRY retry counter. If a parity error persists after ten tries, it is considered a hard error. If ten retries
have not occurred, a branch is made to RETRY and the sequence repeated.
If the Parity Error bit of the RXES is not set, then the program tests to see if the CRC Error bit is set. If a CRC en-or
is detected, the program increments and tests the CTRY retry counter. If a CRC error persists after ten retries, it is
considered a hard error. If ten retries have not occurred, a branch is made to RETRY and the sequence repeated.
A seek error is assumed if neither a CRC nor a parity error is detected. An Initialize (lNIT) instruction is performed
(paragraph 4.2.7). During a Write or Write Deleted Data function, the sector buffer must be refilled, because INIT
will cause sector 1 of track 1 of drive 0 to be read, which will destroy the previous contents of the sector buffer. The
instruction sequence for a Fill Buffer function is not included in Figure 4-8, but is presented in Figure 4-10. After
the system has been initialized, the program increments and tests the STRY retry counter. If a seek error persists
after ten tries, it is considered a hard error. If ten retries have not occurred, a branch is made to RETRY and the
sequence repeated.
4.5.2 Empty Buffer Function
Figure 4-9 shows a program for implementing an Empty Buffer function with interrupts turned off (lOF). The first
instruction sets the number of retries at ten. A 2 is set in the AC to indicate an Empty Buffer command, and the
command is loaded. When TR is set, the program jumps to EMPTY to transfer a word to the BUFFER location. A
jump is made back to loop to wait for another TR. This process continues until either 64 words or 128 bytes have
been emptied from the sector buffer. When Done is set, the program tests to see if the Error bit is set. If the Err,or
bit is set, the program retries ten times. If the error persists, a hard parity error is assumed, indicating a problem in
the interface cable.
4.5.3 Fill Buffer Function
Figure 4-10 presents a program to implement a Fill Buffer function. It is very similar to the Empty Buffer example.

4-10

IPROGRAM~ING EX"MPLES rOR

ITHE rOl.1.01ollNG "RE RXU lOT CODE OEFINITIOt-.lS
I
ITHE ST"NDARO lor DEVICE CODE IS 67~·

4
5
6
7
8
9
1111
11
;;.2
13
14
15
16
17
18

6701
6702
67"3
671114
670'
67f1J6
6707

4111
41
42
43
44
45

ITO WRITE, WRITE DELETED DATA, OR REAU AT SECTOR "5" (THE CO~TENTS or PROGRAM
I
ILOC"TION SECTOR) or TRACK "T" (THE CONTENTS or PROG~A~ LOCATION TRACK)
I

lIN 8 OR 12 BIT MODE
I

START,

"'20"
"'2211
"'202
"2213
"'2~4

"'21115

1261

flJ21l'1
flJ211

1262
67e11

flJ213
flJ214

"'21'
"'216

flJ217
flJ22fIJ
flJ221
111222
flJ223

6703
'217
1264
671/J2
720111

/I 0" 67X:' TO
IWA I T rOlll TRANSfER REQUEST F'I.AG
I 1 TO HeOCTAL)
IIOT TO 1.0AD SECTOR
ICLA 8£CAUSE lOT XOR ~OESN'T

STR
JMF' ,·1
HO SECTOR
)(DR
CI.A

IWAIT rOR THE TRANsrER REQUEST FLAG THEN TAANsrE~ THE TRACK ADDRESS
I
/I OT 6'X3 TO
STR
tWAIT 'O~ TRANSfER REQUEST
JMP ,-1
I II TO 11410CTAL)
HO TRACK
IIOT TO 1.0AD TRACK
XCR
ICI.A BECAUSE lOT XOR DOESN'T
CI.A
/THE SECTOR AND TRACK ADORESSES HAVE: tl[EN TRANSF'[R"~o TO THE RXU VIA THE XDR lOT
I
IWAIT rOR THE DONE rl.AG AND CHECK rOR ANY ERRORS
I

Ilr

THE rUNCTION HAS COMPI.ETED SUCCESsrul.l.Y INO [RROR rl.AGl THEN HAI.T

111224
"'22'
"'226
111227

6705
'224
67"4
741112

/I OT 67X' TO
IWAIT rOlll OO~E FI.AO
II OT 67X4 "''''PI.ES ERROR rl.AG
I OK - COM"I.[TED

SON
JM" ,.1
SE"
loll. T
I

ITHE ERROR rl.AG IS SET
I
/THE CONTENTS OF' THE TRA~SF'e:R REGIST[H IS THE ERROR STATUS
I
/IF TRANSF"!:R REGISTER BITS 1111, ANC 11 • fIJ THEN SOME TY"E oF' IEEI( ERRoR HAS OCCUREC,
II F' TRANSF'!:R Rr:G I STER BIT 11 0 1 THEN
CRC ERROR HAS OCCUREO,
II r TRANsr!:R REG I STER BIT 10 • 1 THEN
PAR I TY ERROR HAS OCCURED
I

"'23"
flJ231
"'232
"'233
"'234
"'235

XOR
OCA
Cl.Io
ANO
SNA
JM"

67"2
3265
73'"
",265
76''''
5241

ItiET CONTENTS or TR (ERROR STATUS)
lAND SAVE
t 2
IHST ro~ "A~!TY tAROR
ISI<IP IF' PARITY tRROR
INOT " PARITV ERROR - MAYBE CRC

ASTATUS
CLA lAC RU
ASTATUS
CLA
TCRC

IA PARITY ERROR HAS oCCUREO
I

84
85

86
"236
"237
"24"

2255
521116
741212

IINCREMENT AND TEST THE PARITY ERROR METRY COUNTER PROGRAM I.OCATION " "TRY"
I
lAND RETRY THE" COMMAND" UNTIl. THE PARITY ERROR RECOVE~S
I
lOR UNTIl. THE PTRY COUNT!:R OVER'LOWS TO III
I
lSI! PTRy
JMP RETRY
IRETRY THE COMMANC
IHARD "A~ITY ERROR
HI.T
I

ITHE ERROR FL,AG IS SET BUT THE ERROR IS NOT A "ARITY ERROR

91
92

TAO UNIT
I.CO

81
82
83

101''' 12-SlT, 10e1 IF' a-SIT
I " I ' \o/~ITE, 14 H' WRITE DEI.ETEO
ICAU, OR 6 If READ
I 21 I ' UNiT 21, 2e1 IF' UNIT 1
II OT ~?X1 TO 1.0AD THE CO"4MANO

TAO MODE
TAO COMM AND

IWA I T rOR THE TRANSF'ER RE:QUEST FLAG TH[N TRANSF'E" THE SECTOR ADDRESS

RETRY,

6703
5212
1263
671112
7211121

8111

93
94
95

ISEEK RETRY COUNTER

"212

68
69

89
9111

COUNTER

65
66
67

87
a8

~ETRV

ICRe; R£:TRY COUNTER

1260

"'21116
flJ207

7111
71
72
73
74
75
76
77
78

KM10
PTRy
I(M10
CTRY
140 KMU
DCA STilly

54
55
56
57
58
61
62
63

I -1I/l
IPARITY

HO
OCA
TAO
DCA

IWRITE, IoIRITE: DELETED DATA, OR READ

59
6111

I NTR 0 67r116
I~I To 671117
I

48
49

SDt~·6Hl'

ITHE fOl.1.01ollNG IS " PROGRAMMING EXAMPI.~ OF THE PROTOCOL ~EQUIRED

5111
51
52

IIOT TO LOAD THE COMMAND,/Iic) IS THI: COMMAND
IIOT TO LOAD OR READ T~~T~ANsrER REGISTER
IIOT TO SKIP ON A TRj<N'srER RE:QUEST F'LAG
IIOT TO SKIP ON ANARROR fL.AG
IIOT TO SKIP ON !-+IE: DONE rLAG
I lAC) = III I NTt-f(RUPT ENABI.E OF'r I eAC) • 1 MEANS ON
IIOT TO INITllLIAE THE RX8/RXU SUBSYSTEM

I.C0 0 67121l
XDR-671212
STR-671213
SER-671114

19
2111
21
22
23
24
25
26
27
28
29
3111
31
32
33
34
35
36
37
38
39

THE RXe/RXell ~·LEl(IBLE DISKETTE

121241
"242
"'243
121244

731211
1.1265
765121
525121

/TEST rOR •
I
Cl.Io
TCRC,
AND
SNA
JMP

CRC ERROR
I 1
IHST ,.O~ A CRC ERROR
15KI" IF' A C~C ERROR
INOT A C~C • MUST BE A SEEI<

CLA lAC
ASTATUS
CLA
SEEK

Figure 4-8 RX8E Write/Write Deleted Data/Read Example (Sheet 1 of 2)

4-11

CRC tRROR HAS OCCURE:O

101/1

lAo
I

101

IlNCRE:ME:NT AND TEST THE CRC E:RROR RETRY COUNTER !DROGRAM \,OCAT I ON

102
103
104
105
106

I
I

lOR UNTI\, THE CTRY COUNTLR OVE:RF'1.0WS TO "
I

lSi! CTRY
JM" RE:TRY
IoI\,T

107
Ul8
1;»9

lHJ

IR£TRY TioIE: COMMAND
IIotARO CRC ERROR

ITHE ERROR F'\,AG IS SET

111

112
113
114
115

ITHE ERROR IS tNOT] A PARITY ERROR AND IS CNOTl A CRC ERROR
I

BE A SE:EK ERROR

ITHEREF'ORt IS MUST

116

117

118
119

CTRY "

lAND RE:TRY THE: COJo1MAND UNTIl. THE CRC ERROR RECOVERS

(CONH:NTS OF' THE TRANSF'E:R RE:GISTER lilTS 11/1, AND 11 • 0)

"251/1

671/17

12111

StE:K,

INIT

IIOT 67X7 TO INITI'\,IAE

121

IINCRE:MENT AND TEST THE: SE:f:K ERROR RETRY COUNTER PROCRAM 1.0CiTION n SHlY "

122
123
J,24

125

lOR UNTI\, THE CTRY COUNTER OVERF'1.0WS TO III

lAND RETRY TIoIE COMMAND UNTIl. THE SEEK ERROR RECOVtRS
I

126
127

128
129

lSi! STRY
JM" RETRY
H\,T

"251
"252
"253

/THE F'OI.\,OWING PROGRAM \,OCATIONS ARE HU'ERENCtD WITHIN TioIIS EXAMP\,E

13111

131

132

111254

7771/1

KM1",

133

134
135
136

/THE F'O!.\,OWING :5 PROGRAM !.oeAlIONS ARt THE: ERROR R£TRY COUNTERS

138
139
14111

144
145

IPROGRAM \,OCATION " MOOt" CONTAINS A 1/1 IF' 12-81T MODE, OR
ICO~TAINS A 11/10 IF' e-91T MODE:

"261/1

"'0131/1

IPROGRAM \,OCATION
I

147

IWRITE

148
149

"261

158
159

161/1

166
167
168
169
170

171
172
173

(~),

COMMAND" CONTAINS THE COMMAND TO BE ISSUED VIA THE LCD lOT

WRITE DE:LE:TEO DATA

(1~),

OR READ

(6),

COMHAllO,

OR EMPTY ElUF'F'E:R
.,

(2)

1<1. OR •• OR

(!!II. OR UNIT 1 (21/1)

IUNIT
I

1/1262

UNIT ,

II, OR 2I/J

IPROGRAM \,OCATION " SECTOR" CONTAINS THE SECTOR ADOqESS (1 TO 32 OCTAL.)
I

"263

SECTOR. "

1 TO 32 OCTAL

IPROGRAM LOCAT I ON " TRACI( •• CONTA I NS THE TRACK AOOlli:SS (I TO 114 OOTAL)

161

162
163
164
165

001/11/1

IPROGRAM \,OCATION " UNIT" CONTAINS THE UNIT OESIGNATION

151
152

153
154
155
156
157

I!I OR In

HODE,
I

146

151/1

IPAR I TV [RROII RE TRY COUNTER
ICIIC ERROR RETRY COUNTER
ISElI( ERROR RETRY COUNTER

PTRY,
CTRY,
STRV,

137

141
142
143

IRe:TRY HIt COMMAND
lio!ARO SEEK ERROR

"264

TRACK,

III TO 114 OCTAL

IPROGRAM 1.0CHION " .STATUS " CONTAINS THE CONTtNTS

or TioIE TIIANSF'ER REGISTER

IAT THE OETECTION OF' AN ERROR (ERROR FI.AG • 1) WHICH CORRE:SPONDS TO THE
I

IERROR STATUS

I.'"
I

IF' S!:EI( E:RROR, 1 IF' CRC E:RROR. i! IF' !DARITY f;RROR

ISTATUS AT ERRoR

ASTATUS,

Figure 4-8 RX8E Write/Write Deleted Data/Read Example (Sheet 2 of 2)

4-12

228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265

ITHE FO~~OWING IS A PROGRAMMING ~XAM~~E Or PROTOCO~ REQUIRED TO
I

I~MPTY

0312
0313
0314
031'
0316
0317
0320

12'4
3255
1377
3010
1260

1261

276

277
278
279
280

281
282
283
284
285

EENTRY, TAD KM10
DCA PTRy
ESETUP, TAO (BUFfER-1)
DCA Al~
TAO MODE
TAD COMMAND

8 TRVS TO EMPTy THE SECTOR BurrER
IPARITV ERROR RETRy COUNTER
IPROCRAMS DATA BUrrER
IAUTO INOEX REGISTER 10
I " I' 12-BIT, 1"0 Ir e BIT
I 2 MEANS EM'TY BurrER
IIOT TO ISSUE THE COMMAND
I

~CO

6701

IWAIT rOR A TRANSrER REQUEST FLAG BErORE TRANsrERRING DATA TO THE 'ROGRAMS
I

IOATA BurrER FROM THE Rxal SECTOR BurrER
I

IWAIT rOR A DONE rLAG TO INDICATE THE COMP~ETION Or THE EM~TV BurrER COMMAND PRIOR TO

ITESTING THE ERROR rLAG

0321

0322
S323
"324
032'

67Q!3
7410
'333
67"5
'274

ELOOP,

ITEST rOR TR rLAG
ITR NOT ItT, TEST rOR DONE r~AG
ITR n.AG SET
ITEST ro_ DONE r~AQ
INOT TR, DR OONE YET

STR
SK"
JM" EMPTY
SON

JMP ELUUP
I

ITHE DONE '~AG IS SET
I

ITEST rOR ANY ERRORS

0326
0327

6704
7402

(ON~V

ERROR POSSIB~E IS A PARITy ERROR)
ITEST rOR THE ERROR r~AG
INO ERRORS • OK

SER

H~T

IINCREMENT AND TEST THE PARITY ERROR RETRY PROGRAM ~OCATloN " PTRY "

lAND RETRV THE COMMAND UNTIL THE tRROR RECOVERS

266

267
268
269
270
271
272
273
274
275

THE SECTOR BUrr~R Or 64 12-BIT WORDS (12 BIT MODE), 0_

IEMPTY THE SECTOR BUrrER Or 128 a-BIT BYTES (8 BIT MODE)

loR UNTl~ THE PTRV COUNTER OVERrLOWS TO 0

1330
1331
1332

I 51 ~TRY
JMP ESETUP

IRE TRY TO EM_TV THE SECTOR Bur'ER
IHARO PARITY ERROR

H~T

ITHE TRANS'ER REQUEST r~AG IS SET
I

ITRANsr~R

0333
0334
033'
0377

6702
341111

EMPTY,

'321

0377
1114"0

DATA TO THE PROGRAMS DATA Bur~ER rROM THE Rxel SECTOR BurrER
IrROM THe Rxel SECTOR BurrER
ITO THE -ROGRAMS DATA BurrER
I~OO~ UNTIL THE OONE r~AG SETS

XDR
DCA r AUl
JMP E~OOP

PAGE
ITHE rO~~OWING PROGRAM ~OCATIONS ARE HrSERVED rOR THE ~ROGRAMS DATA BurrER
I

BurrER,

·SUF'ER+200
S

Figure 4-9 RX8E Empty Buffer Example

4-13

ITHE ro~~owlNG IS A PROGRAMMING EXAMP~E OF PRUTOCJ~ REQUIRED TO

174
175
176
177

I
I~I~~

17B

I~I~~

179

I
A10"111'
I

lB~

181
182
183
184

1/J0111J

"266
"267

"27i!1

185

~271

187

"272
"273

186
lBB

12'4
32"
1377
312110

12611J

FENTRV, TAO KM1"
~CA PTRy
TAD (BUFFER-l)
DCA A1~
TAD MODE
~CD

IWAIT FOR A TRANSFER REQUEST F~AG BErORE TRANsrERRING DATA FROM THE PROGRAMS

19~

IOATA BurFER TO THE RX"l SECTOR BUFFER

191

193
194

IWAIT FOR A OONE r~AG TO

2212

I~DICATE

THE COMP~ETION or THE 'I~~ BUFrER COMMAND PRIOR TO

ITESTING THE ERROR rLAG

195

201

I S TRYS TO 'l~~ THE SECTOR BurFER
IPARITY ERRO~ RETRV COUNTER
IPROGRAMI DATA BurrER
IAUTO INOEX REGISTER 18
I I!I I' u·sn, 10" Ir 8 BIT
IIOT TO ISSUE THE COMMAND

192

200

THE SECTOR BurFER WITH 128 a-BIT BVTES (8 BIT ~OOE)

SETUP,

6701

189

196
197
198
199

THE SECTOR BUFFER WITH 64 12-9IT WORDS (12 SIT MOOE), OR

11J274
11J27'

67"3
741121

"276

'306

11J277
"30i!1

LOOP,

67'"
5274

STR
SKP
JMP '-II.~
SON
JMP ~OOP

IT[ST '-OR TR F~AG
ITR NOT lET, TEST 'OR DONE FLAG
ITR 'I.AG SET
ITEST 'OR OO~E r~AG
INOT TR, 0- OONE YET

203

ITHE OONE 'LAG IS SET

204
205

ITEST FOR ANY ERRORS

206

207
208

67''''
741212

209
210
211

(ON~Y

ERROR POSSIB~E IS A PARITy ERROR)

SER

ITEST 'OR THE ERROR r~AG
INO [RRORS • OK

H~T

IINCREMENT AND TEST THE PARITY ERRoR RETRY PROGRAM LOCATION" PTRV "
I

lAND RETRy THE COMMAND UNTI~ THE ERROR RECOVERS

212
213
214

lOR UNTIL THE PTRY COUNTER OVERF~OWS TO "

215

2255
'279
'41212

216
217

21B

151 PTRy
JMP Se;TUp

TO 'I~L THE SECTOR eu,rER
IHANO PA~ITY ERROR

I~ETRV

H~T

219
220

222

ITRANSFER DATA FROM THE PROGRAMS DATA BUrFER TO THE RXl!l1 SECTOR BU,rER

ITHE TRANS'ER REQUEST F~AG IS SET

221

223
224

225

"306
"307

226
227

"310
11J311

1410

6711J2
72""

5274

FI~~'

TAD I AU
XOR

IVIA AUTO INOEX REGISTER 18
ITO THE RXll SECTOA BurrER
IC~A BECAUSE lOT XOR DOESN'T
I~OOP UNTI~ TME DONE F~AG SETS

C~A

JMP LOOP

Figure 4-10 Fill Buffer Example

4-14

4.6 RESTRICTIONS AND PROGRAMMING PITFALLS
A set of 11 restrictions and programming pitfalls for the RX8E is presented below.
1.

When performing the following sequence of instructions, interrupts must be off.

[ ~~:-----------SDN
JMP
(done)
(fill or empty buffer)

If interrupts are not off, the following sequence of events will occur. Assume interrupts are enabled and
the RX8E issues an interrupt request just before the SDN instruction. The SDN instruction will be
executed as the last legal instruction before the processor takes over. However, since the Done flag is
cleared by the SDN instruction, the processor will not find the device that issued the interrupt.
2.

The program must issue an SER instruction to test for errors following an SDN instruction.

For maximum data throughput for consecutive writes or reads in 8-bit mode, interleave every three
sectors; in 12-bit mode, interleave every two sectors. (This of course depends on program overhead.)

When issuing the lOT XDR at the end of a function to test the status, the instruction AND 377 must be
given, because the most significant bits (0-3) contain part of the previous command word.

If an error occurs and the program executes a Read Error Register function (111) (paragraph 4.4.7), a
parity error may occur for that command. The error code coming back would not be for the original
error in which the Read Error Register function was issued, but for the parity error resulting from the
Read Error Regis~er function. Therefore, check for parity error with the Read Status function (101)
before checking for errors with the Read Error Register function (111).

The SEL DRV RDY bit is present only at the time of the Read Status function (101) for either drive, or
at completion of an Initialize for drive O.

It is not necessary to load the Drive Select bit into the command word when the command is Fill Buffer
(000) or Empty Buffer (001).

Sector Addressing: 1-26 or 1-328 (No sector 0)
Track Addressing: 0-76 or 1-1148

If a Read Error Register function (111) is desired, the program must perform this function before a
Read Status function (101), because the content of the Error register is always modified by a Read
Status function.

10.

The instructions STR, SDN, SER also clear the respective flags after testing, so that the software must
store these flags if future reference to them is needed after performing one of these instructions.

11.

Excessive use of the Read Status function (101) will result in drastically decreased throUghput, because a
Read Status function requires between one and two diskette revolutions or about 250 ms to complete.

4-15

4.7 ERROR RECOVERY
There are two error indications given by the RX8E system. The Read Status function (Paragraph 4.4.5) will assemble
the current contents of the RXES (paragraph 4.3.6), which can be sampled to determine errors. The Read Error
Register function (Paragraph 4.4.7) can also be used to retrieve explicit error information.
The results of the Read Status function or the Read Error Register function are in the Interface register when Done
sets, indicating the completion of the function. The XDR lOT must be issued to transfer the contents of the
Interface register to the PDP-8's AC.
NOTE
A Read Status function is not necessary if the DRV RDY bit is
not going to be interrogated, because the RXES is in the
Interface register at the completion of every function.
The error codes for the Read Error Register function are presented below.

Octal
Code
0010
0020
0030

0040
0050

0060
0070
0110
0120
0130
0140
0150
0160
0170
0200
0210

Error Code Meaning
Drive 0 failed to see home on Initialize.
Drive 1 failed to see home on Initialize.
Found home when stepping out 10 tracks for INIT.
Tried to access a track greater than 77.
Home was found before desired track was reached.
Self-diagn os tic error.
Desired sector could not be found after looking at 52 headers (2 revolutions).
More than 40 ps and no SEP clock seen.
A preamble could not be found.
Preamble found but no I/O mark found within allowable time span.
eRe error on what we thought was a header.
The header track address of a good header does not compare with the desired track.
Too many tries for an IDAM (identifies header).
Data AM not found in allotted time.
eRe error on reading the sector from the disk. No code appears in the ERREG.
All parity errors.

4-16

Reader's Comments
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