Digital PDFs

EK-RP056-MM-001

December 1975

113 pages

Original

6.4MB

Document:	RP05/RP06 Device Control Logic Maintenance Manual
Order Number:	EK-RP056-MM
Revision:	001
Pages:	113
Original Filename:	EK-RP056-MM-01_maint_Dec75.pdf

OCR Text

RPOS/RP06 device
control logic
maintenance manual

·-----digital equipment. corporation · maynard. massachusetts-----......

RPOS/RP06 device
control logic
maintenance manual

EK-RP056-MM-OOl

digital equipment corporation • maynard. massachusetts

1st Edition, December 1975

Copyright © 1975 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.

DISCLAIMER
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.

The following are trademarks of Digital Equipment
Corporation, Maynard, Massachusetts:
DEC
FLIP CHIP
DIGITAL
UNIBUS
DECUS

PDP
FOCAL
COMPUTER LAB
MASSBUS

CONTENTS
Page

CHAPTER 1
1.1
1.1.1
1.2
1.2.1
1.2.1.1
1.2.1.2
1.2.2
1.2.3
1.3
1.3.1
1.3.2
1.3.2.1
1.3.2.2
1.3.3
1.3.4
1.3.5
1.4
1.5

GENERAL . . .
System Compatibility
PHYSICAL DESC:RIPTION
Card Ne:st and Cable Assembly
Hex Printed Circuit Boards
MASSBUS and MDLI Interface PCBs
Power Supply
....... .
Power Monitor . . . . . . . .
DCL FUNCTIONAL DESCRIPTION
Dual Controller Operation
Read/Write Data Transfers ..
Disk Paek Fonnatting
Other Read/Write Commands
Disk Addressing Techniques and Rela.ted Commands
DCL Interface Registers . . . . . . .
Error Correction Capability . . . . .
APPLICABLE INSTRUCTION MANUALS
SPECIFICATIONS . . . . . . . . . . . . .

CHAPTER 2

THEORY OF OPERATION

2.1
2.1.1
2.1.1.1
2.1.1.2
2.1.1.3
2.1.2
2.1.2.1
2.1.2.2
2.1.3
2.1.3.1
2.1.3.2
2.2

DEVICE CONTROL LOGIC, SIMPLIFIED BLOCK DIAGRAM DISCUSSION
Asynchronous Transfers and Control Command Execution
Dual Control Operation . . . . . . .
Register Select Decoding and Registers
Command Decoding . . . . . . . . .
Synchronous Data Transfers . . . . . . . .
Synchronous Data Transfer Commands
Synchronous Data Transfer Control Logic
Disk Addressing Logic . . . . . . . . .
Cylinder /Track Addressing (Seek)
Sector Addressing . . . . . . , . .
MASSBUS AND MDLI (DRIVE) INTERFACE SIGNALS
Massbus Interface Signals
MDLI (DRIVE) Interface Signals
COMMAND REPERTOIRE
Control Commands
Data Transfer Commands
Housekeeping Commands
Mechanical Movement Commands
DETAILED BLOCK DIAGRAM DISCUSSION
Massbus Control Signal Routing and DCL Interface Registers
Control Line Enabling Signals
Attention Summary Register Access
DCL Interface Registers . . . . . .
Synchronous Data Flow . . . . . . . . .
Write Operation (Massbus·to·Dilsk Transfer)
Read Operation (Disk·to·Massbus Transfers)

2.2.1

2.2.2
2.3
2.3.1
2.3.2
2.3.3
2.3.4
2.4
2.4.1
2.4.1.1
2.4.1.2
2.4.1.3
2.4.2

2.4.2.1
2.4.2.2

INTRODUCTION

iii

1·1
1·1
1·1
1·2
1·6
1·6
1·6
1·6
1·6
1·6

1·9
1·9
1·9
1·10
1·10
1·11
1·11
1·11

2-1
2-1

2·1
2·1

2·3
2-3
2-4
2-4

2-5
2-5

2-6
2-6
2-6
2·9
2-9
2-9
· 2·10
· 2-11
· 2-12
· 2-12
· 2-12
· 2-12

· 2-16
· 2-16
· 2-29
· 2-29
· 2-32

CONTENTS (Cont)

Page
2.4.3
2.4.3.1
2.4.3.2
2.4.3.3
2.4.3.4
2.4.3.5
2.4.3.6
2.4.3.7
2.4.3.8
2.4.4
2.4.5
2.4.5.1
2.4.5.2
2.4.5.3
2.4.6
2.4.6.1
2.4.6.2
2.4.6.3

Basic Clock and Index Pulse Distribution
Basic Clock Signals . . . . . . .
Sync Clock Generator Circuits ..
Ring Counter . . . . . . . . . . .
Byte Counter and Byte Count Shift Register
Sync Clock Enable Control and Sync Clock Enable Flip-Flop
Sector Clock Counter and Sector Counter . . . .
Sector Compare Logic and Desired Sector Register
.... .
Sector Found Control and Sector Found Flip-Flop . . . . .
Sector Format and Related Control/Synchronization Requirements
Disk Addressing Logic, Block Diagram Discussion
Cylinder Addressing
Track Addressing . . . . . . . . . . . . . .
Sector Addressing . . . . . . . . . . . . .
Error Correction Code Logic Block Diagram Discussion
Generating and Writing the EeC Field (Write Operation)
Checkout of the ECC Redundancy Code (Read Operation)
Error Correction Processing . . . . . . . . . . . . . . . .

CHAPTER 3

SERVICE INFORMATION

3.1
3.2
3.3
3.3.1
3.3.2
3.3.3
3.3.3.1
3.3.3.2
3.3.3.3
3.4
3.4.1
3.4.1.1
3.4.1.2
3.4.1.3
3.4.2
3.4.2.1
3.4.3
3.4.3.1
3.4.3.2
3.4.4
3.4.4.1
3.4.5
3.4.5.1
3.5
3.5.1
3.5.2
3.5.3

GENERAL . . . . . . . . . . . . . . . . . . . . . . . .
DCL POWER SUPPLY AND POWER MONITOR
ASYNCHRONOUS DATA TRANSFER (HANDSHAKE)
Writing a Register
Reading a Register "
Dual Control . . . . .
Port Acquisition
Port Release
Simultaneous Controller A and Controller B Demands
MECHANICAL MOVEMENT
Seek
Seek Flow
Implied Seek . . .
Mid-Transfer Seek
...... .
Offset
Offset Flow
Return-to-Centerline ..
Return to Centerline Flow
Implide Return to Centerline
Recalibrate . . . . . .
Recalibrate Flow
Unload . . . . . .
Unload Flow
SECTOR SEARCH . . .
Sector Timing
Sector Search Flow
Implied Search ..

· 2-33
· 2-33
· 2-36
· 2-37
· 2-37
· 2-37
· 2-38
· 2-38
· 2-38
· 2-38

.240
.248
.249
· 2-50
· 2-50
· 2-52
· 2-52
· 2-53

3-1
3-1
3-2
3-2
3-3
34
34
3-5
3-5
3-5
3-5
3-5
3-6
3-6
3-6
3-7
3-8
3-8
3-8
3-8
3-8
3-9
3-9
· 3-10
· 3-10
· 3-10
· 3-10

CONTENTS (Cont)
Page

3.6
3.6.1
3.6.2
3.6.3
3.6.3.1
3.6.4
3.6.5
3.6.5.1
3.6.6
3.6.7
3.6.8
3.7
3.8
3.8.1
3.8.2
3.8.3
3.8.4
3.8.5
3.8.6
3.9
3.10
3.10.1
3.10.2
3.10.3
3.10.4
3.11
3.11.1
3.11.2
3.12
3.12.1
3.12.2

WRITE HEADER AND DATA FLOW DIAGRAM DISCUSSION ..
Command Setup . . . . . . .
Sector Search/Sector Found
Pre-Header Field . . . . . . .
Writing the Sync Byte
. . . . . .
Header Setup Operations and Writing the Header
..,....
. . . . . .
Header Gap
Data Field Sync Byte
Data Field . . . . . . . .
Error Correction Code (ECC) Field
Data Gap . . . . . . . . . . . . .
HEADER COMPARE PROCESS . . . .
WRITE DATA FLOW DIAGRAM DISCUSSION
Command Setup . . . . . . . . .
Pre-Header Field and Header Field .
........... .
Header Gap
Data Field Sync Byte and Data Field
ECC Field . . . . . . . . . . . . .
. .... .
Data Gap . . . . . . . . . . . . . .
READ DATA COMMAND/READ HEADER AND DATA COMMAND
FLOW DIAGRAM DISCUSSION
HOUSEKEEPING COMMANDS
No Operation (No-Op)
Read In
.....
Pack Acknowledge ..
NG Drive Clear . . . .
BYTE COUNTER OPERATION
Shift Clock Select
Byte Count Development
ERROR HANDLING AND ECC HANDL][NG
Error Handling
ECC Handling

CHAPTER 4

REPLACEMENTlPROCEDURES

4.1

GENERAL . . .

CHAPTERS

MAINTENANCE

5.1

GENERAL . . .

APPENDIX A

INTEGRATED CIRCUIT DESCRIPTION

· 3-10
· 3-11
· 3-11

· 3-11
· 3-11

· 3-12
· 3-12
· 3-12
· . 3-12
· 3-13
· 3-13
· 3-13
· . 3-15
· 3-15
· 3-15
· 3-15
· 3-15
· 3-15
· 3-16
· 3-16
· 3-18
· 3-18
· 3-18
· 3-18
· 3-18
· 3-18
· 3-18
· 3-18
· . 3-19
· 3-19
· . 3-20

. . . . . . . . . . . . . . . . . . . . . . . . . . . ..

4-1

. . . . . . . . . . . . . . . . . . . . . . . . ..

5-1

ILLUSTRATIONS
Figure No.
1-1
1-2
1-3
1-4

1-5
1-6
2-1
2-2
2-3

24
2-5
2-6
2-7
2-8
3-1
3-2

3-3
3-4

3-5

3-6

Title
Drive and DCL Assembly
. . . . . . . . . .
Drive and DCL Assemblies Rear View, Rear Panels Removed
DCL Rear View, Card Nest and Cable Assembly Extended
Card Nest and Cable Assembly PCB Layout
DCL Assembly Front View, Front Panel Removed
DCL Assembly Power Supply, Front Pan,~l Removed
Device Control Logic, Simplified Block Diagram ..
Massbus and MDLI (Drive) Interface Signals . . . .
DCL Interface Registers and Massbus Control Signal Routing Block Diagram
Synchronous Data Transfer Path Block Diagram . . . .
Basic Clock and Index Pulse Distribution Block Diagram
Sector Format (16 Bit Mode) Diagram
Disk Addressing Logic Block Diagram
Error Correction Logic Block Diagram
Move Timing Diagram . . . . . . . .
Implied Seek Timing Diagram
Implied Return to Centerline Timing Diagram
Sector Search Timing Diagram . . . . . . . .
Header Compare Timing Diagram . . . . . .
Data Field Timing - Read Data and Read Header and Data

Page
1-2
1-3
14

1-5
1-7
1-8
2-2
2-7
· 2-13
· 2-30
.. 2-34

· 2-39
· 2-47
2-51

3-6
3-7
3-9
· 3-10
· 3-14

· 3-17

TABLES
Table No.
2-1

2-2

Titlle
DRY/pIP/ATA Status During DCL Operation
Sector Format Processing for Read/Write Commands

Page
· 2·18
· 2-41

CHAPTER 1
INTRODUCTION

1.1 GENERAL
This manual describes the Device Control Logic (DCL) incorporated in the RPOS and RP06 Disk Drives. The Drives
are divided into two major functional parts (Figure 1-1):
1.

The DeL, which houses the necessary logic circuits to interpret and implement all commands executable
by the Drive and allows for access by two diffenmt controllers.

The disk storage drive, which houses the circuits for: rotating the disk pack, positioning the read/write
heads at the addressed cylinder track and sector, and writing/reading bits on the disk pack surface.
NOTE
The primary functional difference between an RPOS and an
RP06 is storage capacity. While an RPOS can address up to 411
cylinders, an RP06 can address up to 815 cylinders; thus, the
storage c~lpacity of an RP06 is almost double that of an RP05.
Except for this difference, the: RP05 and RP06 have the
identical interface to the DCL.. Henceforth in this manual
when descriptions are applicable to both the RP05 and RP06
the description will simply refer to them as Disk Drives. When
the description is different for the two Drives, the differences
will be noted.

1.1.1 System Compatibility
The DCL is capable of handling data transfers in either 16·· or 18-bit format making the Drivec;: compatible with the
PDP-ll, PDP-IS, and DECsystem-l0. Each system has its own specialized controller that inte·faces the Drive with
the related processor.
1.2 PHYSICAL DESCRIPTION
The DCL itself is a 9-inch wide by 32-inch deep by 3S-inch high unit that attaches at the left of the Drive assembly
when the Drive is viewed from the front (Figure 1-1). The DCL assembly is attached to the drive assembly by four
2-inch long 1/4 X 20 bolts. Levelers are attached to provide stability when the DCL is permanently installed.
Physically, the DCL is comprised of thrlee main subassemblies: The card nest and cable assembly, the power supply,
and the power monitor (Figures 1-2, 1-3 and 1-5).

1-1

DEVICE
CONTROL
lOGIC (DCl)

DRIVE
ASSEMBLY

ASSEMBLY

7777-2

Figure 1-1 Drive and DCL Assemblies

1.2.1 Card Nest and Cable Assembly
The card nest and cable assembly is accessible through the rear of the unit by lifting the entire rear cover panel and
drawing it free of the assembly. This exposes the two fasteners that are used to hold the card nest and cable
assembly (Figure 1-2) in an upright position. Then access to the printed circuit cards is gained by:
1.

Loosening the two fastener screws and carefully swinging the assembly outboard until it rests in a
horizontal position.

Loosening the two fastener screws (Figure 1-3) on the air flow cover and swinging the cover to the
vertical position. This exposes the hex and interface printed circuit boards (PCB's).

All control logic circuits are housed on the hex PCBs that extend the full length of the card nest and cable assembly.
The PCBs that interface with the drive assembly and the two controllers are the smaller PCBs situated to the left of
the assembly when viewed from the top. Figure 14 shows the layout of the PCBs within the card nest and cable
assembly.

1-2

DRIVE ASSEMBl V

___

DCl

ASSEMBLY

FASTENER
. SCREWS

CARD NEST

AND CABLE
ASSEMBLY

7777-1

Figure 1·2 Drive and DCL Assemblies Rear View, Rear Panels Removed

1-3

FASTENER
SCREWS

AIR FLOW
COVER

CARD NEST
AND CABLE
ASSEMBLY

7777-5

Figure 1-3 DCL Rear View, Card Nest and Cable Assembly Extended

1-4

7777-4

Figure 14 Card Nest and Cable Assembly PCB Layout

1.2.1.1 Hex Printed Circuit Boards - There are five hex PCBs. Designations for these cards are based on the
principal control circuits housed on a particular PCB. For example, the Error Correction (EC) PCB is s~ designated
because there are more ICs used for this function than for any other control function on this particular;board. This
does not mean, however, that other ICs on this same PCB are not used for control functions completely *nrelated to
error correction. The designations used are simply a convenient means of labeling and identifying the hex PCB's. The
hex PCBs are broken down as follows:
RG (Registers) PCB: This board contains most of the registers used to interface the DCL with the control1er.
DP (Dual Port or Dual Controller) PCB: This card contains logic used to implement DCL accessing by either
of two controllers.
SS (Seek and Search) PCB: This board primarily includes the control logic to execute all mechanical
operations.
SN (Synchronous Transfer) PCB: Much of the logic on this board implements synchronous data transfers
between controller and disk pack.
EC (Error Correction) PCB: Approximately half of the logic on this PCB implements the error correction
process. The remaining logic is used for error registers and timing.
1.2.1.2 MASSBUS and MDLI Interface PCBs - Of the e:lght interface PCBs, six are used to convey signals between
the DCL and Massbus A/Massbus B. Each of these six PCBs has two cable connectors (11 , 12) mounted directly on
the card to accommodate the appropriate Massbus cables. Figure 1-4 shows the MASSBUS PCB ldcations and
deSignations.
The two interface cards closest to the hex PCBs house the transceiver circuits for conveying signals between the
Drive and the DCL. These PCBs are called the MDLI interf:lce cards (Figure 1-4).
1.2.2 Power Supply
The front of the DCL Assembly houses the H764 supply that develops operating voltages for the card nest and cable
assembly. This unit is accessible from the front of the DeL assembly when the front panel is removed (figure 1-5).
Access to the voltage adjust potentiometers is via the metal hole plugs. The power supply components (Figure 1-6)
can be replaced by removing the four front panel screws shown in Figure 1-6.
The power supply attaches at its base to a mounting bracket located in the center of the DCL assembly. The top
attaches to a bracket directly above the front panel.
1.2.3 Power Monitor
The power monitor is situated beneath the power supply (Figure 1-5) and provides a constant check of the power
supply output voltage conditions. When any voltage (line or dc output) strays from the required tolerance (ac low or
dc low), this unit notifies the system. The power monitor also provides the "power OK" signal used to initialize the
Drives following power up. The power monitor attaches at the base of the DCL assembly with four mounting screws.
1.3 DCL FUNCTIONAL DESCRIPTION
1.3.1 Dual Controller Operation
The DCL interface logic is designed to permit access by two different controllers (Le., provided that the. dual access
option is installed). The setting of the CONTROL switch on the control panel determines whether a single or both
controllers are allowed to access the Drive. When set to the center pOSition, it allows for accessing by either
controller on a "first-come, first-serve" basis. Once a controller has gained access in the dual access mode, it retains
control until it has completed its operation. Nonnally, a controller releases the DeL by executing a release command
to place the Drive back in a device available status. However, if the accessing controller fails to execute such an
instruction within a one-second time span (Le., following the last operation), a timeout function produQes the same
result.
1-6

FRONT
PANEL
SCREWS (4)

H764 POWE R SUPPLY

OUTPUT
VOLTAGE
ADJUSTMENTS

POWER MONITOR

7777·6

Figure 1-.5 DeL Assembly Front View, Front Panel Removed

1-7

7777-3

Figure 1-6 DeL Assembly Powe-r Supply, Front Panel Removed

1-8

1.3.2 Read/Write Data Transfers
Writing data words onto the disk pack or reading data words from the disk pack are termed synchronous data
transfers since such transfers are effected over the synchronous data bus portion of the MASSBUS interface. Four
read/write commands are implemented by the DCL logic. However, the write header and data command must first
be used to format a disk pack (divide the disk surface into addressable sectors) as a prerequisite to executing the
other three commands.
1.3.2.1 Disk Pack Formatting - Each new disk pack must be formatted to provide each sector with an identifying
indicator or label that defines sector number, track number, and cylinder number. This labeling information is
inserted into what is called the header area of a sector, which can also contain additional identifying information
(key field data) under program control. Because the header area is positioned before the data field of a sector, the
header area information can b(~ used to accurately address specific disk pack sectors for a read/write operation.
To format a new disk pack, use the write header and data command. Prior to executing this command, the central
processor writes the initial cylinder~, track, and sector address information into the appropriate DCL registers. The
central processor has the header information (cylinder, track, sector, and key field words) ready on the synchronous
data lines so that when the command is executed and the addressed sector is found, the header information is
present for writing onto the disk. The header information is supplied to the Drive by the operating system.
Executing the write header and data (;ommand causes the DCL to initiate the process of finding the addressed
cylinder, track, and sector. When all are found, the DCL informs the controller to send the header information. At
this time, the DCL also initiates the sequence for serially writing each header word onto the disk surface. In this
way, header information is introduced onto an addressed seetor"
The write header and data command also allows for writing data words beginning at a fixed time following the
header. The area where data words are written is called the data field.
1.3.2.2 Other Read/Write Comm::mds - The DCL interprets and executes three other commands to effect
read/write data transfers. For each of these commands, th(~ DCL makes proper identification of the header prior to
initiating the transfer process. The technique for header identification is to compare the cylinder, sector, and track
addresses of the header against those supplied prior to the read/write command initiation. Failure to detect a
rnatchup in all three addresses results in the DCL setting a h~~ader compare error bit that is eventually sampled by the
central processor.
A breakdown of the remaining read/write commands and their functions is given below:
Write Data Command: This command is used to write data words into the data field of an addressed sector.
The DCL executes this command. by first finding and identifying the addressed sector and then initiating the
write transfer into the data field of that sector. The command can be used for an extended (multi-sector) write
operation in that the DeL continues to write into the data fields of successive sectors for as long as the RUN
line from the controller is asserted.
Read Header and Data Command: This command reads the header and data fields of an addressed sector and
sends both to the central proces.sor via the contro]]l~r. Reading the header information may prove useful in
analyzing faults after the DeL has indicated a header eompare error on a particular sector. By reading the
header information (cylinder, track and sector address) and comparing it against that supplied with the read
header and data command, the CPU is able to determine exactly what header (format) information is in error.
Read Command: This command is used to read the data field of an addre'ssed sector. As is the case with all
read/write commands, the CPU must load the desired cylinder address and desired sector/track registers prior
to executing the command. Once the addressed sector has been found, the DCL reads consecutive sectors for
as long as the RUN line from the controller is asserted.

1-9

1.3.3 Disk Addressing Techniques and Related Commands
The DCL executes two commands that are used solely to locate addressed areas of the disk pack - seek and search.
The functions carried out by these commands are broken down as follows:
Seek Command: This causes the drive read/write heads to be positioned over the addressed cylinder. Cylinder
and track information is supplied from the central processor prior to executing the command. When the heads
are correctly positioned, the drive informs the DCL which in turn asserts the ATTENTION line to the
controller.
Read/Write commands may also require positioning the read/write heads at the addressed ayHnder. This
activity is referred to as an "implied seek", since the seek command is not used and the ATTENTION line is
not asserted.
Search Command: The search command is used as a method of optimizing the pack revolution time. When the
DCL detects the addressed sector, it asserts the ATTENTION line to the contro11er.
1..3.4 DCL Interface Registers
The DCL has 16 interface registers that can be accessed by the controller; they fal1 into the fo]]owing general
ca tegories:
Control - The control register receives the command (read, write, seek, etc.) codes from the controller. The
DCL control logic samples the content of this register and initiates the appropriate execution sequence.
Status - The bits of this register supply the central processor with DCL and Drive status information.
Maintenance - The maintenance register is used by diagnostic programs to initiate various maintenance
functions.
Error Information - Three registers are provided to indicate error status within both the DCL and the Drive.
Address Data - These are five registers that are associated with disk addressing:
•

Desired Cylinder Address Register

•

Current Cylinder Address Register

•

Desired Sector/Track Register

•

Offset Register, used to offset the disk read/write heads in fixed increments.

•

Look Ahead Register, can be used to subdivide the data field of a sector.

System Housekeeping - There are two registers used for system housekeeping, i.e., a drive type register and a
serial number register.
Attention Summary Pseudo Register - This is a one bit register used to indicate that the Drive requires the
attention of the system. In one sense it can be considered an interrupt line.
Error Correction - There are two registers used to convey error correction information to the central
processor.

1-10

1.3.5 Error Correction Capability
The DCL is equipped with error correction logic, which (provided it is not inhibited by the system) becomes
operative whenever an error is detected during a read operatiion. Once activated, the error correction circuits proceed
to locate the area in the sector data field where the error occurred. When this area is detected, the DCL makes
available the following information to the operating system:
1.

Error correction code burst pattern.

Position with the data field where the error occurred.

Given this information, the software can determine the exact bits in error and correct them.

1.4 APPLICABLE INSTRUCTION MANUALS
Instruction manuals bearing upon use of the Drives depends on whether the device is configured in a PDP-II or
PDP-IO system environment (or both). When used with the PDP-ll, applicable instruction manuals are:
•

RP05/RP06 Disk Drive Installation Manual (EK-RP056-IN-001)

•

RJP05/RJP06 Moving Head Disk Subsystem Maintenance Manual (EK-RJP05-MM-OOl)

•

RPO 5 /RP06 DCL Print Set

When the Drive is used with the PDp··10 system, related handbooks are:
•

RP05/RP06 Disk Drive Installation Manual (EK-RP056-IN-OOl)

•

RH10 Massbus Controller Maintenance Manual (A-MN-RH10-0-MAN1)

•

RP05/RP06 DCL Print Set

Manuals related to the Disk Drive are:
•

Memorex RP05/RP06 Operation and Maintenance Manual (EK-RP05M-MM-V01)

•

Memorex RP05/RP06 677-01/677-51 Disk Storage Drive Illustrated Parts Catalog (EK-RP05M-IP-V01)

•

Memorex RP05/RP06 SOO Disk Storage Subsystem Tester Operator's Manual (EK-RP05M-OP-V01)

•

Memorex RP05/RP06 677-01 Logic Manual (EK-RP05M-TM-V01)

1.5 SPECIFICATIONS
Data Format Option:
20 sectors per data track (256 IS-bit words per sector data field).
22 sectors per data track (256 16-bit words per sector data field).
Error Handling:
Error Detection and Correction Capability.
In terface Characteristics:
MASSBUS ControlJer to device interface Dual Controller capability.
System Compatibility:
Can be used in PDP-II or PDP-l 0 system configUifation.

1-11

Data Transfer Modes:
Single sector or multisector (spiral or extended read/write) transfers.
Operating Temp. Ranges:
15° C minimum to 32° C maximum.
Humidity Range:
20% minimum to 80% maximum.
Dimensions:
9-in. wide by 35-in. high by 32-in. deep.
Weight (DCL only):
100 lb (approx).
Operating Voltages DCL only:
+5 Vdc
-15 Vdc
+15 Vdc

1-12

CHAPTER 2
THEORY OF OPERATION

2.1 DEVICE CONTROL LOGIC, SIMPLIFIED BLOCK DIAGRAM DISCUSSION
Figure 2-1 is a simplified block diagram of the DCL indicating the major functional areas involved in accessing the
Drive unit (asynchronous operation) and the implementation of synchronous data transfers. This diagram also shows
the duality of the Massbus interface (the DCL can be accessed by either of two controllers).
2.1.1 Asynchronous Transfers and COl1ltrol Command Exec:ution
2.1.1.1 Dual Control Operation - Asynchronous transfers between DCL and contro11er take place over the Massbus
control lines and occur when the controller writes or reads a register within the DCL. Between controllers, access to
the DCL registers is on a :first-come·first·serv~ basis. Once the DCL is selected by a controller, the enabling signals
(indicated in Figure 2·1 as CONTROLLER SELECT) permit transfers only to/from that controller.
2.1.1.2 Register Select Decoding nnd Registers - Register addressing is also an integral part of the asynchronous
transfer process. The address: of the register tQ be accessed is sent over the Massbus register select lines and
multiplexed in the same manner as the control line signals. The output of the register select multiplexer is applied to
register select decode logic which decodes the five bit address and then generates an enabling signal to the proper
register for the register read or register write operation.
The DCL has 16 Massbus drive registel'S, all of which are readable by the controller. About half can also be written
into by the controller. The DCL registers fall into the following categories:
Control Register - This read/write register receives all command codes from the controller and stores the
command for the duration requin~d to execute the command.
Status Register - This read only register provides status information to the controller regarding the state of
the drive and regarding conditions within the DCL itself.
Error Registers - The DCL has three read/write error registers to convey Drive and DCL error information to
the controller.
Maintenance Register -- A re:ad/write maintenance register that can be used for diagnostic purposes is
provided.
Attention Summary Pseudo Register - There are two of these read/write registers (one for each controller) if
the dual controller configuration is used.
Disk Addressing Registers - The DCL has five registers that are involved in accessing data from the disk. Three
are read/write; two are read only.

2·]

SYNCHRONOUSADATA LINES ,--_ _....
TO CONTROLLER A

SYNC
DATA
LINE
MUX
TO CONTROLLER B ( .

~~--------,

--'
t

....'",...--------Io....--

CONTROLLER
SELECT

SYNCHRONOUS
DATA LINES
FROM CONTROLLER A

FROM CONTROLLER B

SYNC
DATA
LINE
MUX

I -_ _ _ _ _ _ _ _ _ _ _ _~I\.
-"

1--------------,...;,/

DATA
BUFFER
REGISTER

REG.
SELECT
MUX

t
CONTROLLER
SELECT
MASS BUS
CONTROL LINES r-----,
TOIFROM CONTROLLER A

.~
.....

TO/FROM CONTROLLER B &LW~

.....

ICLOCKS

READ/WRITE

DECODE

COMMANDS

DCL

CONTROL~ INTERFACE
LINE

TSHIFT

REG
SELECT

.--_~t--,

<:=)

DATA
BITS TOI
FROM
DRIVE

NOTE

t-----II\.")

FROM CONT B - - - - -..

/,'----1

SHIFT ' . _
- _---I READI
........----~REGISTER! "f
WRITE
CONTROL
-;
GATING

L.---IV~

FROM CONT A

r----..., SEE

Vt'-------t
I\..

PLOI READ DATA STROBE

SYNCHRONOUS
DATA TRANSFER
CONTROL LOGIC

FROM
DRIVE

SECTOR CLOCK
INDI:::X PULSE

BYTE

CONTROL
REG.
OUTPUTS

ICLOCK
COMMAND
DECODING

BYTE COUNTS

BYTE
COUNTER

SECTOR
COUNT

REGISTERS

MUX
SECTOR

SEARCH
COMMAND

CONTROLLER
SELECT

COMPARE
LOGIC

DESIRED
SECTOR ADDRESS
OFFSET MODE
SEEK DIRECTION

SEEK COMMAND
NOTE:

Data bits to / from the
drive use a common pair
of lines.

CYL,TRACK AND SECTOR ADDRESS

rsEcTOR
FOUND

DISK
ADDRESSING
LOGIC

TO
DRIVE

CYLINDER DIFFERENCE, HEAD
ADDRESS AND OFFSET VALUE

)

OFFSET
DRIVE ERROR INFORMATION

11 -2473

Figure 2-1 Device Control Logic, Simplified BJock Diagram

Serial No. and Drive Type Registers - These two read only registers are used for system housekeeping.
ECC Position and Pattern Registers·- These two read only registers are used for error correction code
handling.
2.1.1.3 Command Decoding - The command decoding logic interprets the outputs of the control register to
determine which of the 17 possible commands is to be executed. Among these commands are the read/write
commands (discussed later) that initiate synchronous data transfers. The seek command (Figure 2-1) is used to move
the disk read/write heads between cylinders.
The offset mode is used to offset the read/write heads from the track centerline. The search command can be used
to detect a particular sector of a track. A more comprehensive breakdown of the command repertoire is given later
in this section.
2.1.2 Synchronous Data Transfers
Once the Drive Unit has been connl~cte:d to a controller and a read/write command has been decoded, synchronous
data transfers are implemented via the four blocks shown ;at the top of Figure 2-1. Controller A or B (having earlier
accessed the DCL and therefore having eontrol) transmits or receives data via the following circuit groups:
Massbus Synchronous Data Line Multiplexer - This logic steers 16/18-bit data words (refer to format bit in
offset register) to or from the controller having access to the DCL. Once a controller has gained access,
enabling signals (indicated here as CONTROLLER SELECT) are generated that permit transfers to/from only
that controller.
Data Buffer Register - This register buffers 16/ IS-bit data words in one of two ways depending on transfer
mode (write/read):
•

During write operations this register accepts the data words from the multiplexer and presents them to
the shift register.

•

During read operations this register accepts data words from the shift register and presents them to the
Massbus.

The time at which the data buffer register accepts a word is governed by the synchronous data transfer control
logic. This logic takes into account such factors as the number of shift clocks required to empty/load the shift
register before loading a new word into the data buffer register.
Shift Register - The shift register fulfills the parallel-to-serial conversion requirement during write operations
and the serial-to-parallel conversion requirement during read operations. These conversions are accomplished as
follows:
•

Write operation: in this case, the shift register accepts 16/18-bit words in parallel from the data buffer
register; then transfers the word a-bit-at-a-time (via the least significant bit position) until all 16/18 bits
have been emptied from the shift register and written onto the disk. At this point the next data word is
parallel loaded into the shift register.

•

Read operation: In this case, the shift register accepts data words a-bit-at-a-time from the disk for
application at the most significant bit position. When 16/18 shifts have been accomplished on the
incoming data, a complete word is contained in the shift register. It is then presented in parallel to the
data buffer register.

2-3

The shift pulses used to clock bits to/from the shift register are supplied from the synchronous data transfer
control logic. The number of shift clocks supplied to fully shift a word depends on whether 16- or I8-bit
words are being transferred.
Read/Write Gating Control Logic - This logic simply gates data from/to the disk depending on whether it is a
read or a write operation. It also governs the length of the registers for 16- or I8-bit mode operation. If the
DCL is in the I8-bit mode, two high order stages of the buffer and shift registers are enabled.
2.1.2.1 Synchronous Data Transfer Commands - The DCL interprets six basic read/write commands for
transferring data words via the synchronous data path. These commands, and only these commands, activate the
synchronous data transfer control logic to implement the data transfers. The six commands are:

Write Header and Data - Used for formatting each sector on the disk. Formatting consists of dividing each
sector into fields to insert gaps of an zeros, control words (header), and data words (data field). This is
necessary so that the DCL can address specific sectors of a track when using the other data transfer commands.
The makeup and structure of the sector format are discussed in a later paragraph of this chapter.
Write Data - Used to write data into the data field of a sector. The address information is specified prior to
executing the write command. The DCL uses this address information to find the correct sectpr and then
initiates the write data transfer.
Read Header and Data - Executed to retrieve the header information as well as the contents of the data field
of a sector. Address information must be supplied prior to executing the command so that the DCJ.- can locate
the proper sector and implement the read transfer.
Read Data Command - Similar to the read header and data command except that only the contents of the
data field are sent to the controller. Again, proper he-ader identification must be made prior to reading the data
field words from the disk.
Write Check Header and Data.
Write Check Data.
2.1.2.2 Synchronous Data Transfer Control Logic - This logic carries out all control operations .inherent in
executing the read/write commands for transferring data from/to the disk. The paragraphs that follow describe some
of the more salient control operations and the reasons for ·them.
•

Read/Write Command Interpretation - The synchronous data transfer control logic must recognize the
type of read/write command being executed to initiate the proper control sequence. That is, the control
sequence employed when formatting a disk through use of the write header and data command is
altogether different from that used when exel:;uting a read data command. Also, the clock signal used to
develop shift clock pulses differs for the write and read modes. Furthermore, the proper control signals
must be sent to the read/write control gating in keeping with the type of operation in progress.

•

Clock (PLO/Read Data Strobe) Sector Clock and Index Pulses - The DCL synchronous <lata transfer
control logic receives clock, sector, and index pulses from the drive. The clock pulse is derived from one
of two source signals depending on read/write mode. When reading, the read data strobe sig~al is used to
develop the shift clock. In write operations, the phase locked oscillator (PLO) signal is used to develop
the shift clock.
The sector clock is used to keep track of and to update the sector count as the disk revolves .beneath the
read/write heads. The sector count is important to the sector addressing technique employed by the
DCL. There can be either 20 or 22 sectors per track depending on word length (i.e., I8-bit or I6-bit).

2-4

The index pulse is used to signify the beginning of each revolution.
•

Shift Clock Pulse Uses -- Since each shift clock pulse represents a serial bit transfer time, it is used for
counting as well as shifting data bits. The four uses of the shift clock pulse are listed below .
1.

Clocks bit serially to/from the shift register for DCL to disk transfers.

Counts the number of bits shifted to determine when the shift register has been emptied or filled.
This is necessary to inform the controller when to take or send a word.

Generates a byte clo(~k so that the DCL is aware of what byte and word of a sector is passing
beneath the disk r(~ad/write heads.

Serves as a clocking source in cyclic redundancy checking.

•

Byte Count Development - The synchronous data transfer control logic employs a byte counter to keep
track of what part of a sector is being accessed. As stated earlier, each sector is broken up into fields
during the formatting process. Each field must contain the same number of bytes when comparing one
sector against another. Also, each field must begin at the proper byte count with respect to the sector
pulse which defines the start of a sector. The synchronous data transfer control logic uses the count
from the byte counter to determine when to read/write sync bytes, header words, and the data words
that make up the data fil~ld of a sector.

•

Sync Clock Generation - The synchronous data transfer control logic also generates the sync clock
signals to the controller that must be issued to effect each word transfer. During a write operation, the
DCL issues the sync clock (telling the control1er to send another word) after the shift register has been
emptied and a word is parallel loaded into the shift register. During read operations, the DCL issues the
sync clock (telling the controller to take another word) after the shift register has been filled and the
word is loaded into the data buffer register.

2.1.3 Disk Addressing Logic
The disk addressing logic actually in~:ludes a number of the registers within the register block on Figure 2~1.
However, the disk addressing logic and sector compare logic are shown as separate blocks on the diagram to
distinguish them as functions and to indicate their relationship to the seek and search commands respectively.
2.1.3.1 Cylinder/Track Addressing (Sc!ek) - To reach an addressed cylinder, the DCL and Drive must execute a
seek, which means that the disk read/write heads must be mechanically moved to the desired cylinder address. The
DCL employs a desired cylinder register (10 bits) to store the new cylinder address and a current cylinder address
register (10 bits) to store the current position of the read/write heads. (In an RP05, 9 bits of the desired cylinder
register are used to address up to 410 cylinders. In an RP06, 10 bits of the desired cylinder register are used to
address up to 815 cylinders.) When the contents of both these registers is the same, no positioning of the read/write
head (seek action) is required. Any change in the contents of the desired cylinder address register initiates a
subtraction process that results in the DeL sending direction and magnitude information to the Drive. This
information is, in turn, used by the Drive to carry out a seek operation. At the conclusion of a seek (meaning that
the heads have been positioned at the desired cylinder), the desired cylinder address (now the current address) is
entered into the current cylinder address register. At this time, both registers contain the same address. Following
this, any updating or change of the contents of the desired cylinder address register results in the DCL and Drive
executing a new seek. Updating the contents of desired cylinder address register can occur in any of the following
ways:
•
The controller executes a seek command. In this case, the desired cylinder address is loaded with the
new desired cylinder address before the seek command code is loaded into the control register.

2-5

•

The controller executes a read/write command having previously loaded a new cyJinder address into the
desired cylinder address register. This type of seek is called an "implied seek", because a seek command
is not being executed, yet a seek operation must take place before the data transfer can start.

•

The desired cylinder address is incremented following the last track of a cylinder when the OCL is
executing an extended read/write operation. This is called a "mid-transfer" seek.

•

A search command is executed and the previously loaded desired cylinder address differs from the
current cylinder address.

The DCL disk addressing circuits employ subtraction logic using the outputs of both the desired cylinder address
(DCA) register and current cylinder address (CCA) register to develop a difference for the Drive. The cylinder
difference (magnitude) of seek is generated by subtracting the contents of the CCA from the contents of the DCA.
The disk addressing logic also supplies a seek direction signal to the Drive, informing it as to which way the
read/write heads must be moved for the new cylinder address.
Track addressing is effective via a five bit portion of the desired sector/track address register and selects the desired
read/write head of the drive.
2.1.3.2 Sector Addressing - New sector addresses accompanying operating system commands are inserted into a
five bit portion of the desired sector/track register. This may be done when the operating system executes a search
or any read/write command.
The DCL employs a sector counter (part of the synchronous data transfer control logic) to maintain synchronization
between the DCL sector timing and the actual disk revolution in relation to the read/write heads. When the sector
count matches the contents of the five bit sector address (in the desired sector/track register), the sector found
condition occurs.
An read/write commands have desired sector addresses accompanying them. When the sector found condition
occurs, it means that the synchronous data transfer control logic can initiate the control sequence for the read/write
transfer.
Clearing the sector counter occurs once each revolution on assertion of the index signal from the Drive.
2.2 MASSBUS AND MOLl (DRIVE) INTERFACE SIGNALS
The interface signals conveying control signals and data words from the DCL to the Massbus and from the DCL to
the Drive are shown on Figure 2-2. These signals and their purposes are described in subsequent paragraphs.
2.2.1 Massbus Interface Signals
Individual Massbus signal lines and signal group lines connecting the controller and OCL are described below:
1.

SYNCHRONOUS DATA AND PARITY (19) LINES - These lines convey I6-bit or I8-bit data and an
associated parity bit. The synchronous data lines are bidirectional and employ odd parity. Data is
transmitted synchronously using the sync dock signal supplied from the DCL and the write clock signal
generated by the controller.

SYNC CLOCK - Developed by the DCL during read/write data transfers to inform the controller to:
•

Accept the data on the synchronous data lines during read operations. The controller accepts the
data on the negation of the SYNC CLOCK signal and the DCL changes the data on the assertion of
the SYNC CLOCK signal.

2-6

MDLI

MASSBUS

...-_ _J

CYLINDER DIFFERENCE I OFFSET
r-_1_0_L_IN_E_S___
I__
5_12__
(O_R_l_2_5_,50
__
, 1_0_0,_2_0_0_,4_O_O_._R_EV
__D_I_R____________

SYNCHRONOUS DATA BUS

RECALIBRATE PULSE
OFFSET MODE LEVEL
OFFSET RESET PULSE

CYLINDER ADDRESS (NEW CYLINDER ADDRESSl
/

19 LINES
18 DATA + PARITY

"'"

3 LINES

• "'Jr---------LOGiC (DCLl

5L1NES

ENO OF BLOCK

St.QUENCE PiCK iN

EXCEPTION

'--

READ/WRITE DATA LEVEL
PORT A LAMP
PORT B LAMP

OCCUPIED (ANT DATA)

'--

t?
-..J

CONTROL BUS

CONTROLLER.., 1
(PORTl
JACK A
JACK B
JACK C

17 LINES
16 DATA + PARITY

DEMAND
CONTROL TO DRIVE (DIRECTION OF TRANS)
DRIVE SELECT
4 LINES

r---------------------~v//
REGISTER SELECT

"
'"

r---------------------~//
V
ATTENTION
INITIALIZE
MASS FAIL

WRITE CURRENT UNSAFE TRANSITIONS UNSAFE
ABNORMAL STOP
CURRENT SINK FAILURE
WRITE READY UNSAFE
READ AND WRITE
WRITE SELECT UNSAFE
MULTIPLE HEAD SELECT INDEX ERROR
CURRENT SWITCH UNSAFE NO HEAD SELECTION
TRANSITIONS DETECTED
PLO UNSAFE
FAIL

"'I

~
~

CONTROLLER
(PORT)
JACK A
JACK B
JACK C

'*" 2

DISK DRIVE

TO ERROR REGISTER #2 (13 LINES)

1/ ~i.;i:A:::::RS

TRANSFER

5 LINES

WRITE COMMAND LEVEL
WRITE DATA STROBE
READ COMMAND LEVEL
DEVICt:. INIIIALi Lt:. t-UL5 t.
PLACE DEVICE IN STANDBY

RUN

'--

HAR1, HAR2,---HARI6

r---------------------------------------------~~

SYNC CLOCK

I\.

HEAD SELECT

WRITE CLOCK

CONTROLLER

CAR 128, CAR 256, CAR 512

CONTROLLED GND (GND TO LOAD HEADS-OPEN LINE WILL RETRACT HEADSY

DEVICE CONTROL

I\.

~_ ~
V

SEEK/OFFSET GO PULSE

VIA1~_ _

SEEK DIRECTION LEVEL (l=REVERSE O=FORWARD)

DIFF=0
STOP VELOCITY
VELOCITY SERVO ENABLE

DC UNSAFE
RESET REGISTERS
SEEK INCOMPLETE
OFF CYLINDER

DC WRITE UNSAFE
AC WRITE UNSAFE
HEADS UNSAFE
ON LINE
SEQUENCE PICK OUT
READ DATA STROBE
PLO CLOCK
OFFSET READY LEVEL
FILE READY LEVEL
INDEX PULSE
SECTOR CLOCK
WRITE PROTECT LEVEL
PLUG ENABLE
PORT A LOCK
PORT BLOCK
UNSAFE
SIGN CHANGE
35V REGULATOR FAIL
LOGICAL ADDRESS 4
LOGICAL ADDRESS 2
LOGICAL ADDRESS 1

~----

CP-2089

Figure 2-2 Massbus and MDLI (Drive) Interface Signals

•

Send the WRITE CLOCK during write operations. This informs the DCL to take the data word on
the synchronous data bus lines.

WRITE CLOCK - This signal is echoed by the controller in response to the SYNC CLOCK during write
operations. On the assertion of the WRITE CLOCK the DCL accepts the data word. On the negation of
this signal, the controller changes the data on the data bus lines.

RUN LINE - After a data transfer command has been written into the control register of the DCL, the
DCL connects to the synchronous data bus. The controller then asserts the RUN line to initiate the
function. At the end of each sector, on the: trailing edge of the EBL (end-of-block) pulse, RUN is
sampled by the DCL. If it is still asserted, the function continues for the next sector; if it is negated, the
function is terminated.

END-OF-BLOCK (EBL) - This signal is asserted by the DCL at the end of each sector (after the last
sync clock/pulse and the two ECC words). For certain error conditions where it is necessary to terminate
operations immediately, EBL is asserted prior to the normal time for the last SYNC CLOCK. The data
transfer is terminated prior to the end of the sedor in this case.

EXCEPTION (EXC) - This signal is asserted when an abnormal condition occurs in the DCL. The DCL
asserts this signal to indicate an error during a data transfer command. EXCEPTION is asserted at or
prior to assertion of EBL and is negated at the negation of EBL.

CONTROL BUS - The parallel control and ~:tatus path consists of a 16-bit parallel data path and an
associated parity bit. The control and status lines are bidirectional and employ odd parity.

DRIVE SELECT - These four lines transmit a 4-bit binary code from the controller to select a
particular DCL/Drive. The DCL responds when the (unit) select number in the DCL corresponds to the
transmitted binary code.

CONTROLLER-TO-DRIVE - This signal is g.enerated by the controller and indicates the direction in
which control and status information is to be transferred. For a contro11er-to-Drive transfer, the
controller asserts this signal. For a Drive-to-controller transfer, this signal is negated by the controller.

10.

REGISTER SELECT - These five lines transmit a S-bit binary code from the controller to the DCL. The
binary code selects one of the DCL registers.

11.

DEMAND - This signal is asserted by the controller to indicate that a transfer is to take place on the
control bus. For a controller-to-DCL transfer, DEMAND is asserted by the contro11er when control line
information is present and settled on the control bus. For a DCL-to-controller transfer, DEMAND is
asserted by the controller to request data and is negated when the data has been strobed off the control
bus.

12.

TRANSFER - This signal is asserted by the DCL in response to DEMAND. For a controller-to-DCL
transfer, TRANSFER is asserted when the data is strobed off of the control lines and is negated when
DEMAND is negated. For a DCL-to-controller transfer, TRANSFER is asserted after the data is asserted
on the control bus and negated when the negation of DEMAND is received.

13.

ATTENTION - This line is shared by all eight DCL's attached to a controller; it may be asserted by any
DCL as a result of an abnormal condition or status change in the DCL. An ATA status bit in each DCL is
set whenever that Drive is asserting the ATTN line.

,2-8

This signal may be assert(~d fiQr any of these reasons:

•

An error, whiile no command is being executed (asserted immediately).

•

At the completion of a. command if an error occurred during execution of the command.

•

Completion of a non-data transfer comma.nd (such as SEARCH).

The ATTENTION bit in a DCL may be cleared by the following actions:
•

Asserting INITIALIZE on the Massbus (affects all eight Drives).

•

Writing a 1 into the Attention Summary register (in the bit position corresponding to the address
of the asserting Drive)" This clears the ATTENTION bit; however, it does not clear the error.

•

Writing a valid command (with the GO bit set) into the DCL Control register when no composite
error is preset. Note that clearing the ATTENTION bit of one DCL does not always cause the
ATTN line to be negated because other DCLs may also be asserting the line.

14.

INITIALIZE - This signal is asserted by the controller to perform a system reset of all DCLs. When a
DCL receives the INITIALIZE pulse, it immediately aborts the execution of any current command.

15.

MASS FAIL - When asserted, this signal indicates that a power-fail condition has occurred in the
controller.

2.2.2 MDLI (DRIVE) Interface Signals
Control and data lines used to transfer signals between the DCL and Drive are also on Figure 2-2. These signals are
described in the handbook for the Drive. Some of the more fundamental signals are shown on Figure 2-1 and
described in the paragraphs covering this illustration.
2.3 COMMAND REPERTOIRE
The subsequent paragraphs describe the reaction of the DCL to control commands, as well as the range and type of
commands executable within the DCL itself.
2.3.1 Control Commands
Execution of a control command by the controller causes transfer of c<;mtrol/status information over the 17 control
bus lines (Figure 2-2).
Execution of a control command by the controller always results in the reading or writing of an addressed DCL
register. Consequently, a register select code, supplied over the five register select lines, must always be present when
the controller executes a command code. ,Further, the DCL device code must also be supplied over the drive select
lines. When the register selected is the control register and the controller writes into this register (i.e., with the low
order bit, called the GO bit, set), om~ of the 17 commands executable by the DCL is initiated.
A summary of the 16 registers that can be sampled and written into by the controller is listed as follows.

2-9

Unibus Address**
(Octal)

Control*

776700

Status*

776720

Error Register No.1 *

776714

Maintenance*

776724

Attention Summary*

776716

Desired Sector/Track Address*

776706

Look Ahead

776720

Drive Type

776726

Serial No.

776730

Offset *

776732

Desired Cylinder Address*

776734

Current Cylinder Address

776736

Error Register No. 2*

776740

Error Register No. 3*

776742

ECC Position

776744

ECC Pattern

776746

*Indicates register can also be written.
**Code conversion of two low order octal digits is accomplished by related controller.

2.3.2 Data Transfer Commands
The DCL executes the following data transfer commands when the related command code is written into the control
register:
1.

Write header and data (formatting), 63 8

Write data, 618

Read header and data, 73 8

Read data, 718

Write check header and data, 53 8 . The decode of this command is ORed with that of the read header and
data. As such the DCL executes the same control sequence.

2-10

Write check data SIs. The decode of this command is ORed with that of the read command. Hence, the
DCL treats it as a read command.

Search. The search command does not actually transfer data. However, it does inform the controller that
the desired sector has been found, and consequently, the software can go ahead and initiate a data
transfer. Its principal uses are in disk use optimization and rotational position sensing.

A brief description of the activities carri(~d out by the DCL for each of these commands is given below:
•

When formatting (write header and data command), the DCL writes aU fields of a sector (including
header field and data field) onto the disk and inserts eJch field in its proper position with respect to the
sector pUlse. (The sector pulse defines the start of a sector.)

•

Write data. This command is used to write the 256-word data field of a sector. The DCL makes proper
identification of the addressed cylinder track and sector by reading and verifying the header before
beginning the write operation.

•

Read Header and Data. When executing this command, both the header and data fields of a sector are
sent to the controller. Proper identification of the sector only is required before the transfer is initiated.

•

Read Data. In this case, the DCL sends only the data field of a sector. Again, proper header
identification is made beforf! beginning the transfer.
Data transfer commands may include an implied seek if the desired cyHnder address (accompanying the
command) does not match the current cylinder address. When there is a difference between the desired
cylinder address and tht~ current cylinder address on execution of a data transfer command, the DCL
executes a seek to positiion the disk read/write heads at the addressed cylinder. The DCL then searches
the disk (on the addressed track) for the desired sector and when found, initiates the data transfer.

2.3.3 Housekeeping Commands
The housekeeping commands used by the DCL and their individual purposes are as follows:
1.

NO-OP. This command does nothing and is used as a filler command by the software.

DRIVE CLEAR. The following registers and conditions within the DCL are cleared by this command.
•

Status Register (AT A and ERR status bits)

•

All three Error Registers

•

Attention Summary Register

•

ECC Position and l~attern Registers

•

The Diagnostic Mode Bit

INITIALIZE SIGNAL. This MASSBUS interface signal performs the same functions as the DRIVE
CLEAR command, but does not require that the Drive be ready (i.e., it bypasses the control register).

PACK ACKNOWLEDGE. This command sets the volume valid bit for the commanding controller. This
command must be issued before any data transfer or positioning commands can be given if the drive has
gone off-line and then on-line. It is primarily intended to avoid unknown disk pack changes.

2-11

READ-IN PRESET. This command sets the W (volume valid) bit, clears the desired sector/track address
register, clears the desired cylinder address regis,ter, and clears the FMT, HCI, and ECI bits in .the offset
register. It is used to bootstrap the device.

RELEASE. This command performs a drive clear function and releases the Drive for use by the other
controller.

2.3.4 Mechanical Movement Commands
All of the below commands require movement of the Drive read/write heads as part of their execution sequence.
1.

SEEK. This command causes the heads to be moved over the desired cylinder. Once the heads are
positioned, the desired cylinder address becomes the current cylinder address since they are now the
same.

OFFSET. This command is executed as a "micro" seek. It allows the read/write heads to be moved
off the track center line. This command is used as part of the error recovery process and requires a
maximum of 10 ms to execute, regardless of the offset value.

RETURN TO CENTER LINE. This command is used to return the read/write heads to the track center
line after an offset operation.

RECALIBRATE. This command positions the read/write heads over cylinder zero, and resets the current
cylinder address register to zero. This command takes a maximum of 900 ms to complete.

UNLOAD. This command is used to place the drive in the STANDBY state. The heads are retracted, the
spindle powered down, and the STANDBY light lit. This command completes when the Drive is brought
back on-line (up to speed and heads loaded).

2.4 DETAILED BLOCK DIAGRAM DISCUSSION
2.4.1 Massbus Control Signal Routing and DCL Interface Registers
A block diagram showing the circuits used to route control line data from/to the controller and all interface control
registers within the DCL is illustrated in Figure 2-3. The command decoding logic used to interpret the contents of
the control register is also shown on this illustration.
Since the DCL can be accessed by either of two controllers, enabling signals that permit transfer to/from one
particular controller at any given time must be generated. A controller gains access to the DCL when it asserts its
DEMAND line at a time when the DCL is free (i.e., at a timl~ when the other controller has not pre-empted the DCL
through an earHer access).
2.4.1.1 Control Line Enabling Signals - The enabHng signals (allowing transfer over the control lines) generated
following access by a controller are defined below:
1.

Controller A has access and is writing a DCL register. Signal DP3 REC CONT EN A H enables the related
receivers to apply the 16-bit control line information to the control bus input multiplexer. Only the
receivers are enabled since the Control-to-Drive (CTOD) signal is asserted when transferring to the DCL
(Figure 2-3).

2-12

MASS BUS

DP3 TRAS A EN H

OPe) c00ABDPe)C~
a
LINES

,..

CONTROL L1NES,CONTROLLER A

DP0 TC00ALDP0 TC!2)7 AL
a LINES

A ATTEN
READ
MUX

16LINES

f '. .

DP5 PORT A ONtO) H
a LINES

DP2 ATA A BITOO LDP2 ATA A BIT 07 L
CONTROL
BUS
OUTPUT
REGISTER

16 LINES
RG2 CONT OR 00LRG2 CONT OR 15 L

16 LINES

CONTROL LINES, CONTROLLER B

DPel TC 08ABDP0 TC 15AB
a LINES
DP!2) C00 ABDP0 C07 AB

DP4

DP3 TRAS B ENH

B:;~~N I~ /~~~~a~L~I~gN~E~~~s~ :~~ 1.~__~1~6~L_I_N~ES~ ~~IT~
t3>

LIl

PARITY
CHECK
OR
GENERAlOR

MASS BUS

a LINES

c-.II

II
11

DP4

__________

______

__________

-..-----~---- ------------~~
••- -__

MeX

~PORTBON'O)H

.
,aLINES
t7\
~---------------------------------------------+rD~p~2~A=TA~B-B--IT-0--0-L----D-P-2-A-T-A-B--B-IT-0--7-L----------------------------~
.-------------~~------------------------------~~--------------------~~------------------------------------------------------~e

RG5 ECC PAT
REG SEL L

ECC PATTERN
REGISTER
(17)

ERROR
REGISTER"'3

EC2 ECC POS REGOOHEC2 ECC POS REG 12(1) H

ERROR
REGISTER"'2
(10)

ADR SEL L

r-'-C-U-R~R-E-N-T---.
CYL ADDRESS
(CCA) REGISTER
(13)

1,0

W:~

SSt CCA OOHSSt CCA 09H

ERROR
REGISTER'" 2/
:#=3 MUX
EGa

r RG5 CUR CYL ADR SEL L I

1 1

DESIRED CYL
ADDRESS (DCA)
REGISTER
(12)
10
LINES

SSt DCA OOHSS1 DCA09H

ECG ERR REG 02100 (1l HEC6 ERR REG 02/15 (llH

~________~~~17r-_______________+~~n+_
~

RG5 CUR CYL

RG5 WRT REG L
16
16
~
LINES

EC7 ERR REG 03/00 (I) HEC7 ERR REG03/15(!) H

ECC PAT/POS
REGISTERS
MUX EC4

ir
I
I

(15)

13
LINES

RG5 ERR
REG 02
SEL L

- RG5 ERR
REG 03
SEL L

RG5 ECCPOS
REG SEL L

ECC POSITION
REGISTER
(16)

II
LINES
ECI ECC PAT REG 2 t HECI ECC PAT REG 31 H

RG5 WRT

RG5 OFF-SET
REGSELL

RG5 SERIAL NO
SEL L

RG5 DRV TYPE
SEL L

RG5WRT
REG L

REG L

OFFSET
REGISTER
(Ill

RG10FFSET 25HRGI OFF SET aOO(t)H,
RGI REV DIR III H,
RGI 22 FORMAT H

SPARE

DCA/CCA
REGISTER
MUX
SS6

8 LINES

1
OFFSET
REGISTER
MUX
RGI

SERIAL NO.
REGISTER
(14)
ECa
16
LINES
HARDWIRED
PER UNIT

DRIVE TYPE
REGISTER
(06)

Eca

16
LINES
HARD WIRED
PER UNIT

SERIAL NO.
DRIVE TYPE
REGISTER
ECa

__------------~~~~+__+I~6L~IN~ES~------~~~n~------------~~H7~------------~f
'-..:...1
~
"-=-.l
RG2 CONT OR OOLRG2 CO NT OR 15 L

NOTES:
1. Not all inputs to multiplexer supplied from
moin! register. see related logic diagram.
2. Outputs too var ied to list
see related logic diagram.

c p - 209 0

Figure 2-3 OCL Interface Registers and Massbus
Control Signal Routing Block Diagram
(Sheet 1 of 2)

2-13

DP3 REC CONT EN A H

a )-------IVRECV

TA0

C00- TC0 C15 Ali

ISLlNES

8 LINES
CONTROLLER
A ATTEN.
REG (04)

b~----------------~~--~I
CONTROL
BUS
INPUT
MUL TlPLEXER

16 LINES
DPO COO ABDPO TC15 AB

DP3 REC CaNT EN B H

IS LINES

C l-------I

TDOCOOBH-

8 LINES

TFOC15BH

CONTROLLER
SiATTEN.
R~G

(Q4)

d~---------"J
~------------------------~'I~-~--~~--~-----------'T------------~----------~

LOOK

RG5
,DES

r-RG5LOOKAHEAD 1
SELL

rRG5MAINTI
REGSELL

~~LGWc"T DE RE8'!~~T~

AHEAD R

REGI STER
(07)

DPS SECTEXTOOENCH,

g~~ ~~~~E;;TO~~(~~H~
DPS SECT CNT 04 H

rRG5STAT
I REGSELLI

r-M....A'-IN-T-E-N-A-N....
}'-E...

,...-...-ER-R-0-R--,1......,

r--'&""S-TA-T-u-s-,l......,

SECTOR/TRACK
REGISHR
(05)

L._ _-r-.....:..;.R..:;,GS~

10
LINES

LINES

iRG5ERR
I REGSELL

RG5WRT REGL
IS
LINES
~

I~~~ ~~C;c~~~~~_H,

SEE NOTE I

ISS3 TR ACK J4H

5 LI NES

ISLlNES

COMMAND
DECODE
LOGIC

r- RG3 WRT CHK DAT L
r-+ RG3 WRT CHK HO AND DAT L

r- RG3 WRT COM L
r- RG3 WRT HDDATCOM L
r-+ RG3 READ COM L

EC9 RUN H
MAINT/ERROR
REGISTER
1
MUX
RG2

'*'

ATT REG
MUX
DP2

I •
ETI.

DECODE
NETWORK

~ :7

r-+ RG3 SEARCH COM L

RG3 FOH
RG3 F4 H

SEE NOTE 2

~
LOOK AHEAD
DESIRED SECTOR
AND TRACK REG
MUX
SSS

r---. RG3 RECAL COM L
r---. RG4 NG DRV CLR COM H
r---. RG3 RELEASE COM L

R..:;,G.=.J3
L._ _--.----.:...:

RG5 WRT REG L

RGO ERR REG 01 (OO){l)HRGO ERR REG 01(15)(I)H

RG 3 UN LOAD COM L

r--.....
lC-O-N-T-R-O-Lla.-,

9
ISS3 SECTDESOOH-

RG 3 NO OP COM L

rRG5CONT

I REGSELL

'---1

STATUSI
CONTROL
REGISTER
MUX
RG6

f-- RG3 READ HD OAT COM L

r---. RG3 SEEK COM L
,~

r--

RG3
~tg'p .-G_O_(_')_L_~

DRIVE
ADDRESS

RG3 OFFSET COM L

L. RG3 RET TO CLR COM L

~ RG4 PACK -ACK H

RG3/RG4~ RG4 READ IN H

L. tJ
~

CP_ 2091

Figure 2-3 DCL Interface Registers and Massbus
Control Signal Routing Block Diagram
(Sheet 2 of 2)

2-14

Controller A has access and is reading one of the: DCL registers. In this case, signal DP3 TRAS A EN H is
asserted to enable the transmitters to send the outputs of the control bus output register/A attention
read multiplexer to the contwller.
NOTE
The eight low order bits from the control bus output
register are taken through a multiplexer that also
receives the outputs of the controller A attention
register" This arrangement permits controller A to
sam]ple the status of the attention register at times when
it does not have control IQf the DCL. This feature is
disclLlssed in a later paragraph.
Because controller A has access in this instance, signal DPS PORT A ON (O) H is not asserted. This
allows the multiplexer to pa.ss on the low order byte from the control bus output register and not the
output of the controller A Attention Register.

Controller B has access and is sending 16-bit information over the control bus. In this case, signal DP3
REC CONT EN B H is asserted in the same way as described for Controller A.

Controller B has access and is sampling the contents of the DCL register. In this case, signal DP3 TRAS B
EN H is asserted in the same way as described for Controller A.

When a controller is sending information over the control bus, it is to write the control information into one of the
DCL registers. The transfer path in this situation involves the receivers, control bus input multiplexer, and the
addressed (selected) register.
To write control data into any register, signal RGS WRT REG L mu~t be asserted (this signal is generated only when
the control-to-drive, CTOD, signal is asserted to indicate that the direction of transfer is to the DCL).
When a register is being sampled by a controller, the routing path is through an associated multiplexer. (In an but
one case, one mu1tiplexer serves two registers.) The signals are then applied to the control bus output register for
transfer to the controller via the related read multiplexer and transmitter circuits.
AIl multiplexer circuits feeding the control bus output re:gister have their outputs wire ORed. The multiplexer
enabling signals that select the outputs of one register rather than another are the same as the signals used to select a
particular register. The register selection signals are listed in the following table:
Registe:r Name

Selection Signal

Control

RGS CONT REG SEL L

Status

RGS STAT REG SEL L

Error Reg No. 1

RGS ERR REG 01 SEL L

Maintenance

RGS MAINT REG SEL L

Attention Summary

DP2 ATA REG SEL AlB H

Desired Cylinder
Address

RGS DES CYL ADR SEL L

2-15

Selection Signal

RG5 CUR CYL ADR SEL L

Error Reg 02

RGS ERR REG 02 SEL L

Error Reg 03

RGS ERR REG 03 SEL L

ECC Position

RGS ECC POS REG SEL L

ECC Pattern

RGS ECC PAT REG SEL L

2.4.1.2 Attention Summary Register Access - The manner and path in which an attention summary register is
sampled by a controller depends on whether the DCL is free for access or currently engaged by one' of the two
controllers. For example, assume that the DCL is not currently engaged and it raises the ATTENTION in;terface line.
Assume further that controller A is the first of the two controllers to sample the attention summary register todetermine which Drive unit raised the ATTENTION line. In such a situation, controller A gains access to the DCL
and samples the attention register via the following path: attention register multiplexer, Drive adclress decode
network, control bus output register, A attention register read multiplexer, and the control1er A transmitter circuits.
If it is further assumed in this example that controller B attempts to read the attention summary rqgister (after
controller A has already gained access), it too can sample the register but the transfer now takes place over a
different path. The transfer path to controller B is directly through the B attention read multiplexer. from Figure
2-7, it can be seen that this in no way affects paths to control1er A which currently has access to the pCL. When
controller B attempts to access the status register after accessing the attention summary register, it is supplied with
an all zeros status, meaning that controller A has control.
2.4.1.3 DCL Interface Registers - The subsequent paragraphs describe the interface registers within the DCL.
•

Control Register (00) and Command Decoding - The control register is addressed (selected) by the
controller when the five Register Select lines convey all zeros. The control register is used to store the
command code as shown below.
15

DVA

DVA-

Device Available
(For status sampling)

FI-FS -

Function Code

GO-

GO bit

Control Regjster Format

2-16

o
Fl

The GO bit can be consildered an extension of the function code since it must be set (and also the RUN
line must be high) for the DCL to execute the specified command. The five bit function (FI-FS)
specifies the type of command to be executed. The Function Code and related commands are listed
below.

Function Code
F4 F3 F2

0
0
0
0
0
0

0
0
0
0
0

1
I

0
0
1

1
1
1
1

0
0
0
0
0

0
0
0

0
0

0
0
0
0
0
0
0
0

1
1

0
0

1
1
0
0
0

1
0

0
1

1
1
0
0

1
0
0
0

Through
1

Command
Fl

0
1
1

0
1

0
0
1
0
1
0
1
0
0
1

No operation
Unload (stand-by)
Recalibrate
Drive Clear
Release (dual-port operation)
Search Command
Write Check Data
Write Check Header and Data
Write Data
Write Header and Data
Read Data
Read Header and Data
Seek Command
Offset Command
Return to Centerline
Pack Acknowledge
Read-In Preset
Illegal Functions

The device available (DV A) bit is used for controller status samp1ing. This bit is set if sampled by the
controller that has gained control of the DCL. I1t is reset (meaning that the device is not available) to the
controller that does not have control.
•

Status Register - The status register informs the controller of various conditions within the DCL and the
Drive. The format and the meaning for each bit position are shown below.

BIT POSITIONS -

,--;...;;.....-r-~....-....;..;...-r

COMPOSITE
ERROR
ATTENTION
ACTIVE

MEDIUM
ON-LINE

POSITIONII'lG
OPERATION
IN
PROGRESS

LAST
SECTOR
TXFRD
WRITE
LOCK

VOLUME
VALID

POGRAMMABLE
(DUAL-PORT)

DRIVE
READY

CP-20BB

2-17

Bits 0-5 are not used.

Bit 6: Volume Valid (W) - The "Volume Valid" status bit indicates when a disk pack may have
been changed, and therefore the program should not assume anything about the identity of the
pack. Even though only one W bit exists in the dual-controller application, W-A is accessible
only to controller A and W-B is access:lble only to controller B. The W status bit is reset by the
DCL whenever the drive cycles up (from the off state). The "Pack Acknowledge" command or
"Read in Preset" command, when receiv(~d from either controller, causes the W bit to set for that
controller.

Bit 7: Drive Ready (DRY) - At the completion of every command, data handling or mechanical
motion, the DCL sets this bit. The controller should not attempt to issue another command if this
bit is reset. This bit indicates the readin·~ss of the DCL to accept a new command. The (DRY) bit
is associated with the following conditions:

•

If the command is a read or wIite type, the setting of the DRY bit indicates normal
termination. If an error was made during data transfer, the appropriate error bits are set as
well.

•

If the command is a mechanical movement command, both the ATA bit and the DRY bit
are set at the completion of the command. If an error was committed during the command,
the appropriate error bits are also set.
The DRY bit status during the vaJious stages of the DCL operation is shown in Table 2-1.
The ATA bit associated with the DRY bit functions is shown in the table only if no error
conditions exist (normal terminati'Dn). At the completion of the operation, the DRY bit is
set.
Tablt~ 2·1
DRYjPIP/ATA Status During DeL Operation

Operation

No Operation
Unload (Stand-by)
Recalibrate
Drive Clear
Release
Search Command
Implied Search
Seek
Offset
Write Check
Write Data
Write Header and Data
Read Data
Read Header and Data
Implied Seek
Mid-Transfer Seek
Return to Centerline
Pack Acknowledge
Read-In Preset

DRY

PIP

ATA at End?
(No Error)
No
Yes
Yes
No
No
Yes
No
Yes
Yes
No
No
No
No
No
No
No
Yes
No
No

0
0

1
1

0
0

0
0
0
0
0
0
0
0
0
0
0
0
0
1
1

2-18

0
1
1

0
0
0
0
0
0
0
1

0
0

Bit 8: Drive Preset (DPR) - On a single-controller type operation this bit is always set. On
dual-controller type operation, this bit will be reset if the DCL is busy from the other controller.
The DPR bit is set again when the Drive switches from the other controller to this one.
In general, setting the DPR bit indicates that the DCL is connected to the asynchronous control
bus of this controller..

Bit 9: Programmable (PGM) - This bit is set when the CONTROL switch is in the neutral (center)
position upon power up, indicating that the device is accessible from either controller A or B.
When the CONTROL switch is in either A or B position upon power up this bit is cleared.

Bit 10: Last Sector Transferred (LST) - This bit is set by the DCL when the last addressable
sector on the disk pack has been read or written. It is cleared by the initialize signal.

Bit 11: Write Lock (WRL) - This bit reflects the status of the WRITE PROTECT switch on the
control panel. When this switch is activat(~d, no write operation can be executed.

Bit 12: Medium On-Line (MOL) - This bit is set by the DCL at the successful completion of the
start-up cycle as follows:
•

Mount Pack

•

Start Spindle Motor

•

Motor Up to Speed

•

Load Heads

With the positioner in recalibrate state (addressing cylinder 0), the device generates a "File-Ready"
condition which is active only if the positioner is settled in the recalibrate state. Upon recognizing
this condition, the DeL sets the MOL bit.
The MOL bit is reset when:
•

The spindle is powered down.

•

The device is switched off-line (with the spindle still up to speed) for diagnostic purposes.
NOTE

WheneveJr the MOL bit changes states (set or reset), the ATA
bit is also set: (except in the unload operation case).
9.

Bit 13: Positioning Operation in Progress (PIP) - Set by the DCL when a pOSitioning function
command is accepted. This bit is reset when the function is complete.
The PIP bit is set during seek, offset, return to centerline, recalibrate, unload, and search
commands. The PIP bit is not set during implied-seeks or mid-transfer seeks.
Table 2-1 shows the conditioning of PIP in relation to the type of operation being performed. At
the completion of the moving operation, the PIP bit is reset and both the DRY and ATA bits are
set (normal termination).

2-19

10.

Bit 14: Composite Error (ERR) - This bit is set when any bit in the error registers (01,02, or 03)
becomes set. This bit summarizes all the errors in the OCL/Drive that are considered important to
the operation.
This bit is reset as fo]]ows:

11.

•

The controller issues a "Drive Clear" command.

•

The controller asserts the initialize (INIT) line.

Bit 15: Attention Active (ATA) - The attention active bit in the status register is the indicator of
the attention condition for the DCL.
The AT A bit can be set only by the DCL. In addition to setting this bit on the status register, the
same conditions control the interface line (ATTENTION) belonging to the attention summary
register.
The conditions for setting the ATA bit and asserting the ATTENTION line are as follows:
•

Any error in the error register causes the AT A Bit/ATTENTION Line to set (except during
data transfers).

•

A positioning operation is completed (Table 2-1).

•

Start-up cycle completion (with MOL Bit set).

•

Dual-Controller operation. Indicates present drive availability (drive was requested before,
but was not available).

NOTE
The ATA bit is not set if the drive is switched from a neutral
position.
The conditions for resetting the ATA bit and negating the ATTENTION line are as fol1ows:

•

The controller issues a "Drive Clear~' command.

•

The controner writes a ONE into the attention summary pseudo register bit position
corresponding to this drive.

•

The controller asserts the initia1ize (init) line on the interface.

Error Register No. 1 - This register informs thl~ controller of specific DCL error conditions. The register
can also be written by the controller for diagnostic purposes. Setting any bit in this register sets the
composite error bit in the status register. The format of this register is shown below.

BIT POSITIONS-

15
14
12
11
10
~--~--~----~--~---r--~----'~~~--~----~---r~~----~--~--~--~

DATA CHECK
ERROR

OPERATION
INCOMPLETE

DRIVE
UNSAFE

WRITE LOCK
ERROR

DRIVE
TIMING
ERROR

ADDRESS
OVERFLOW
ERROF!

INVALID
ADDRESS
ERROR

HEADER
COMPARE
ERROR

HEADER
CRC
ERROR

ECC
"HARD"
ERROR

WRITE
CLOCK
FAIL

PARITY
ERROR
FORMAT
ERROR

ILLEGAL
REGISTR

ILLEGAL
FUNCTION
11-2606

2-20

The meanings of the individual bits are as fol1ows:
1.

Bit 0: Illegal Function (ILF) - This bit is: set when the function code in the control register does
not correspond to an :implemented command. This bit is reset when a "Drive Clear" command is
issued or an initialize (INIT) pulse is received.

Bit 1: Illegal Register (ILR) - This bit is set when the DCL decodes a nonexisting register address
on the register select lines.

NOTE
Atte:mpting to write into a read only register does not
cause the (lLR) bit to set. The bits received are ignored
and no other error condition is flagged.
This bit is reset when a Drive Clear command is issued or an initialize (INIT) pulse is received.
3.

Bit 2: Register Modification Refused (RMR) - This bit is set when a "Write" is attempted into
any register (except th~~ Attention Summary Register) during an operation.
During an operation only two registers can be written:
•

Main tenance Register

•

Attention Summary Register

When the RMR bit is set~ the DCL continues to execute the command in progress. This bit is reset
when a "Drive Clear" command or an initialize (INIT) pulse is received.
4.

Bit 3: Parity Error (PAR) - This bit becomes set under the two conditions given below.
•

When a parity error is detected during data transmission over the synchronous or
asynchronous data Jines (odd parity) during a "Write" operation. The detection of a parity
error causes the DCL to set the "Exception" line and set the PAR bit in the error register.
The DeL continues accepting data as if nothing happened until the end of the sector. At the
trailing edge of (EBL), the DCL samples the RUN line and takes the following actions:
If the RU1\I-line is high, the DCL maintains the PAR bit and EXCEPTION line set and
continues writing on the next sector as if nothing happened. At the end of transfer the
ATA b:it is set.
If the RUN-line is low, the "Write" command wi11 be terminated with the ATA bit and
EXCEPTION line set, in addition to the PAR error bit.

In either of the foregoing cases, the EXCEPTION line is reset at the trailing edge of the EBL
pulse.
•
5.

When a parity error is detected on the asynchronous control bus while writing a register.

Bit 4: Format Error (FER) - This bit is set during header verification when bit 12 of the first
header word fails to match bit 12 of the offset register. This error bit usually indicates the case
where the wrong pack is mounted on the Drive Unit. If the error is detected, all synchronous
commands except read header and data will abort. This bit is cleared by a Drive Clear command or
the initialization signaL

2-21

Bit 5: Write Clock Fail (WCF) - This bit is set if (during a write operation), no write clock signal
from the controller is detected. Upon recognizing this error condition, the DCL ,aborts the
command. This bit is cleared when a "Drive Clear" command or an initialize (lNI;r) pulse is
received.

Bit 6: ECC Hard Error (ECH) - This bit is set when the outcome of the error ,correction
procedure is such that the error is ECC noncorrectable. This bit is cleared when a "Drive Clear"
command or an initialize (INIT) pulse is received.

Bit 7: Header Compare Error (HCE) - This bit is set by the DCL when the header information
read from the addressed sector fails to match the desired address information (cylinder, $ector, and
track addresses) accompanying a read/write command. If the DCL sets this bit, no trarsfer takes
place except in the case of read header and data command when headers are transfe(red to the
controller even though header errors are detected. This bit is reset when a "Drive Clear'~ command
or an initialize (INIT) pulse is received.

Bit 8: Header Cyclic Redundancy Check Error (HCRC) - This bit is used to indicate a, CRC error
in the header field. It is possible for tht! cylinder address and sector/track address words of the
header to compare successfully (no HCE), but because of an error in the key field words (or the
CRC word itself), the HCRC bit can become set. With this bit set, the DCL does not make any
data transfer. In the event of a CRC error during a "Read Header and Data" command, ,the header
words are transferred to the controller. This bit is reset when a Drive Clear command or an
initialize (INIT) pulse is received.

10.

Bit 9: Address Overflow Error (AOE) - This bit is set during any synchronous transf¢r after the
last addressable sector has been transferred and the RUN line is stiI1 asserted. Once set, the DCL
terminates the operation. The AOE bit is reset when a "Drive Clear" command or an initialize
(lNIT) pulse is received.

11.

Bit 10: Invalid Address Error (lAE) - This bit is set when a seek/search operation is initiated and
the address in the desired cylinder address register or desired sector /track address register is invalid.
The DCL format allows for 20 sectors per data track (I8-bit word data fields) or 22 $ectors per
data track (I6-bit word data fields). The DCL distinguishes between the two formats and sets the
IAE bit if a sector greater than 19 is requested from a 20-sector disk pack (I8-bit word data fields).
A similar action occurs if the cylinder and track addresses exceed the Drive capability.

NOTE
When this error bit is set, any intended operation will not take
place.
The IAE bit is reset when a "Drive Clear" command or an initialize (INIT) pulse is received.
12.

Bit 11: Write Lock Error (WLE) - A manual WRITE PROTECT switch can place the Drive in
"Write Lock" during normal operation. If the Drive is in the "Write Lock" mode and the operating
system attempts to issue a write command, the "Write Lock Error" (WLE) bit is set. The WLE bit
is reset when a "Drive Clear" command or an initialize (INIT) pulse is received.

13.

Bit 12: Drive Timing Error (DTE) - This bit is set when a failure has occurred in the «locking or
timing circuits of the Drive. A failure in the clocking or timing circuits cannot guarantee the logic
remaining in the proper sequence. Consequently, in both the read or write operation, the DCL
aborts the command as soon as this error is detected. In the "Write" case, the software.should try
to regenerate the sector where the error occurred. Setting the DTE error bit includes those cases
where the rise of a sector pulse is encountered before the data transmission is finished, This bit is
reset when a "Drive Clear" command or an initialize (lNIT) pulse is received.
2-22

14.

Bit 13: Operation Incomplete (OP!) - This error bit can only be set when the Drive is not
positioning the read/write heads and is set under the following conditions:

•

A read or write command, involving header search, has not begun transmitting data (sync
clocks) within three index pulses.

•

During a "Search" operation, and in the case where a "Sector Count" match is not made,
the OPI bit is set after a maximum of three index pulses have been encountered.

The DCL continues n~trying for as long as the software wishes. This bit resets when a "Drive
Clear" command 0Jr an initialize (INIT) pulse is received.
NOTE
In general, the OPI bit is used to indicate every case where,
following a command initiation, there is inactivity for a period
of three index pulses.
With the OPI bit set, the GO-bit is cleared and the DeL is
returned to the ready state (the RDY bit is set).

15.

Bit 14: Drive Unsafe i(UNS) - This bit is set when the drive recognizes a condition that prevents
the Drive from operating. Usually this bit being set reflects an "emergency" situation where the
heads are automaticallly retracted and/or the drive is cycled down. If executing a "Drive Clear"
does not cause the UNS condition to disappear, the Drive must be powered and cycled-up again to
assure clearing all the errors including the UNS bit. With the UNS bit set, the DCL cannot
guarantee correct lresults of any of the operations. In most cases, clearing the UNS bit requires
field service intervention.

16.

Bit 15: Data Cheek Error (DCK) - This bit is set during a "Read" operation when the ECC
hardware has deteeted an ECC error after the ECC bytes have been monitored. The DCK bit is
handled as follows:

•

If "Error Correction Code/Inhibit'" (ECI) Bit is OFF, the DCL enters into the error
correction process. The DCK bit remains set during the error correction procedure. This bit
is cleared whl~n a "Drive Clear" command or an initiaJize (INIT) pulse is received.

•

If "Error Conection Code/Inhibit" (ECI) Bit is ON, even though an ECC error is detected at
the end of data transmission, the error correction is inhibited.

With the DCK bit set, the data transfer on the present sector terminates normally and if the
RUN-line remains high at the fan of the EBL Pulse, the command continues on the next sector.
This bit is reset whl~n a "Drive Clear" command or an initialize (INIT) pulse is received.
NOTE
The EXCEPTION line is asserte:d at the completion of the
error corr(~ction process and lasts for the duration of EBL.

2-23

•

Maintenance Register - This register implements maintenance and diagnostic functions within the DeL.
AU bits can be read or written. The format for this register is shown below.
CONTROL BITS
SECTION

FUNCTION BITS
SECTION

SYNC BYTE
DETECTED

ECC
ENVELOPE

DATA FIELC
ENVELOPE
CP-2087

The Diagnostic Mode (DMD) bit must be set before the DeL can be placed in a diagnostic mode. With
this bit set, the device handles the same command repertoire as it norma]]y does.
The maintenance register provides wrap-around capability within the DeL. By using a program
controlled clock the data is shifted through various registers and brought back to memory without being
written on the disk. The wrap-around capability does not check the read/write electronics, but goes as
far as the shift register. The wrap-around capability operates only under the diagnostic mode.
•

Attention Summary Register - This register can be considered a pseudo register because it appears as an
8-bit register from a system standpoint, but is implemented as a single bit (in a different bit position
however) in each Drive. Also aU eight Drives in a system respond when this register is accessed. By
looking at which bit positions are set, the operating system can determine which Drive(s) require
servicing. From a system standpoint, the physical Drives and related bit positions (on the Massbus
control lines) are broken down as fonows:
Prime No.

Bit

Massbus Control Line

00 (ATAOOh

01 (ATAOlh
2

02 (ATA02h

07 (ATA07h

Hence the single attention bit for drive zero is used to indicate the attention active condition for drive
zero etc.

2-24

The controller normally requests "Attention Summary" status from a11 drives simultaneously by
indicating a "read from Register-04" on the register select lines on the Massbus interface. When
"Register-04" is selected, each device places the output of its "attention active" (AT A) flip-flop on its
assigned bit position on the asynchronous control bus.
A particular attention r,egister flip-flop is cleared when the control1er writes a one on the related control
line. The operating system norma]]y clears the attention register when the contro11er accesses a drive, i.e.,
immediately after recognizing that an attention line has been raised. In dual control1er operation, the
attention bit for both controllers is set under the fonowing special conditions:
1.

Upon powering up the Drive from the off·state, attention active goes to both control1ers.

Upon powering up the Drive from the standby state, attention active goes to both controllers
(even if the device is seized by one of the con trollers).

In case of a persistent error, the Drive :is forced to the neutral state. Unless it has already been
requested by the othler controller, no attention active is generated until a request comes through.
When a controller clIears the attention register on accessing the DeL/Drive, it clears only the
related flip-flop. That is, control1er A dears only the flip-flop associated with control1er A and
controller B clears onlly its related flip-flop.

•

Desired Sector/Track Register - One register is used for sector and track addressing since only five
dedicated bits are required to address the 22 possible sectors or 19 possible tracks. The format of this
register is shown below:
15

'-------

I-

TFtACK ADDRESS

SECTOR ADDRESS
11-2602

Invalid address errors are generated by the DCL if the address information supplied by the controller
exceeds the maximum number of accessible sectors/tracks.
•

Look Ahead Register - This register is incorporated to provide the software with a means of optimizing
the disk access time by minimizing rotational delays. The format of this register is shown below.

I:I_EI
\

SC3

SC2

I I I I
07

SC1

sc~

EXTO I

.,..-~

SECTOR COUNT FIELD
(CURRENT SECTOR tIDDRESS)

EXTENSION FIELD
(FR ACTION OF A SECTOR TIMING)
EXT1 EXTIO
0

1'ST QUARTER

2'ND QUARTER

3'RD QUARTER
4'TH QUARTER
CP-2086

2-25

The two fields of the register are described below.
a.

Extension Field. This 2-bit field is essentially a counter that develops the internal timing within a
sector. The counter is always cleared to zero state at the rise of each sector pulse. The counter
divides the sector roughly into fourths (=:200 /1s).

Sector Count Field. The purpose of this field is to address the required sector on the data track,
through an exclusive OR arrangement, with the "desired sector/track address" register. The sector
count field is always being updated. Each time the index pulse is encountered, the sector count
field resets to zero, at the rise of the index pUlse. The maximum count of the sector counter is:

o through 21 if 16-bit word/ da ta field format.

o through 19 if IS-bit word/data field format.
•

Drive Type Register - This is a jumper rather than flip-flop type register and is cut at installation to
provide proper coding information. This register permits the controller/software to distinguish between
different classes of drives. The format is below.
07

OT07I OT~61 OTssl OTg41 OT~ IOTaz IOT~ OTg~1
~

DRIVE TYPE NUMBER
NOT
BLOCK
ADDRESSED

MOV ING
HEAD

D RIVE REQUEST
REQUIRED
11-2604

Bits O-S are used to identify the device type ,so that the system can distinguish between types of disk
drives, tape drives etc.
Bit 11 is the Drive request required (DRQ) bit and is hardwired to always indicate a "1" when the drive
is to be operated in a dual port environment.
Bit 13 is used to indicate that the Drive is a moving head (MOH) device. Since the RPOs and RP06 fall
into this category, this bit is hardwired to the S€:t state.
Bits 14 and IS are always zero for the Device since it is not a tape drive and it is block (sector)
addressed.
The drive type register is aSSigned with the following numbers for the RPOs and RP06 Disk Drives:
Drive Type Register
(Octal)

Designations

020021
024021
020022
024022

Single-Port RPOs
Dual-Port RPOs
Single-Port RP06
Dual-Port RP06

2-26

•

Serial Number Register ,- Like the drive type register, this register also employs jumpers. Its purpose is
to allow identification of the Drive unit to distinguish it from other Drives, possibly of the same type,
attached to a single controllj;'lr.
It differs from the "drive type" number in that the "drive type" refers to different types of Drives, such
as RP04s and RP06s.

•

Offset Register - This re:gister is used for data recovery purposes. Its format is shown below.

BIT LOCATIONS

113

OF5

OF41 OF3

I I
OF6

OF21 OF1 1 OF.

OFFSET INFORMATION (MAGNITUDE/DIRECTION)

FOI~MAT

SIGN
CHANGE

I3IT

ERROR
CORRECTION
CODE
INHIBIT

OFFSET REGISTER
11- 2598

Bit 0-7 contain offset information which dictates how far (in microinches) from the centerline the
read/write heads are to be positioned to implement the data recovery operation.
NOTE
Nmmally the offset register is used only when data
reCI()Vel-Y is unattainable through use of ECC processing.
The selectable read/writ,e h(~ad position offsets are given as follows:

Value/Direction

Code Word OFO - OF7

Position

1st Offset
2nd Offset
3rd Offset
4th Offset
5th Offset
6th Offset

OF7

OF6

OFS

OF4

OF3

OF2

OFt

OFO

(Microinches)

0
1
0
1
0

0
0
0
0
0
0

0
0
1
1
1
1

1
1
0
0
1
1

0
0
0
0
0
0

+200
-200
+400
-400
+600
-600

Return to Track ICen terline

Bit 11 is used for the headler compare inhibit function. The software operating system has the option of
inhibiting header comparison technique used for sector identification. The DeL, upon recognizing this
bit high, ignores the header compare logic and eRe correction.
With the HeI bit set, the DeL depends only on the sector count desired sector address for sector
identification. If the sector count happens to be out of sequence, the wrong sector may be accessed.
2-27

Bit 11 provides the error correction inhibit function. By setting this bit, the software can disable the
error correction code handling logic. When this bit is c1eared during a read data transfer and an error is
detected at the end of a transmission, the DCL immediately enters the ECC correction process. At this
time, the DCL also sets the data check error (DCK) bit in error register 01.
When the results of ECC processing are available, the DCL places the error pattern and the location of
the error pattern (within the data field) in the appropriate ECC registers. If the error is ECC
non-correctable, the DCL also sets the "ECC Hard Error" (ECH) bit. If the ECI bit is set, the ECC
correction process is inhibited. However, the DCK bit is stil1 set on detection of an error.
•

Desired Cylinder Address Register - The format of this register is shown below. Its function and use are
described in the subsection covering the disk addressing logic. Ten bits are used to address the available
cylinders in the disk drive.
15

J
DESIRED
CYLINDER
ADDRESS
11- 2601

•

Current Cylinder Address Register - This register always stores the actual cylinder address where the
disk read/write heads are now positioned. Its format is the same as the desired cylinder address register
and is more fully discussed in the subsection on the Disk Addressing Logic.

•

Error Register Numbers 2 and 3 - These registers are used to receive the error bits suppJied from the
drive via the MDLI interface lines (Figure 2-2). The formats for both registers are shown as foHows.

BIT POSITIONS _

~--.----.---'r---.----r---'r---'.----r---.----~---r---'----~---r---'---'

NOT
USED

PLO
UNSAFE
SPARE

INDEX
ERROR

MULTIFLE
HEAD
SELECT
NO
HEAD
SELECT

NOT
USED

ABNORMAL TRANSITIONS
DETECTED
STOP
FAILURE

WRITE
READY
UNSAFE

TRANSITIONS
UNSAFE

CURRENT
SWITCH
UNSAFE

READ
AND
WRITE

CURRENT
SliNK
FAILURE

WRITE
SELECT
UNSAFE

WRITE
CURRENT
UNSAFE

ERROR REGISTER NUMBER 2
CP-2083

DC-LOW

OFF
CYLINDER

OPERATOR
PLUG
ERROR
SEEK
INCOMPLETE

35V

REGULATOR
FAIL
AC-LOW
NOT
USED

SPARE

DC
UNSAFE
WRITE
AND
OFFSET

ERROR REGISTER NUMBER 3
CP-2084

2-28

•

ECC Position Register - Following the completion of the error correction procedure, this register
contains the exact locatlon of the error burst wilthin the data field.
Upon completion of the ECe process, the DCL loads this register with the necessary information for
processor software examination and analysis.

•

ECC Pattern Register -- This register contains the actual error burst which becomes available at the
completion of the DCL error correction process.
The processor software use:s the contents of the ECC position register to find the actual location of the
error burst in the data field. Then the error burst itself determines the bits in error within the 11 bit
field.

2.4.2 Synchronous Data Flow
Figure 24 shows a block diagram of the circuits used to implement data word (synchronous) transfers between
controller and disk. The data path for both 16 and I8-bit transfers is the same with only minor differences in
handling techniques required.
2.4.2.1 Write Operation (Massbus..to-Disk Transfer) - Data words placed on the Massbus for transfer to the disk
travel through the following circuits before being sent to the disk circuitry:
1.

Controller A/controller B Drive transceiver PCB modules.

Data input multiplexer llogic.

Data buffer register.

Data shift register. All transfers up to this point are made in para]]el - that is, 16 or 18 bits at a time.
Conversion from parallel to serial transfer is effl~cted here in the shift register.

Write gating logic.

Phase set up flip-flop.

Minimum device level interface (MDLI) circuits.

Data words supplied over either Massbus are taken through respective Drive transceiver modules for application to
the data input multiplexer circuits on the error correction module. The level of signal DPS PORT B2 ON H governs
whether the data word is accepted from Massbus A or Massbus B. When asserted, indicating that controller B has
access to the disk, only data words from Massbus B are accepted by the data input multiplexing logic. When this
signal is negated, Massbus A has access and only words from it are accepted. Signals PARITY and RUN are also
received into the data input multiplexing circuits from which they are sent to the parity check and control logic
respectively.
The data buffer register is used to temporarily store data in both read and write operations. Since a write operation
is being performed, signal SNI READ ENABLE L is not asserted, meaning that the data buffer register accepts data
words from the data input multiplexer rather than the shift register.
For both write and read operations, signal SN4 BUF CLK L strobes each data word into the data buffer register. For
a write operation, this signal is developed as fo]]ows:
•

When the DCL is ready to load the data buffer register, it issues the Bus Sync Clock to the controller.

2-29

,-----------------------------------------------------;0

,----------------------------------------------1b

NOTES:
1.

.--------------~

THE 18 DATA LINES FROM THESE PCBs ARE: TAO DIOOAH-TAO DI05AH, BIT 00 THROUGH 05
TBO DI05AH-TBO Dl11AH, BIT 06 THROUGH 11
TCO DI12AH-TCO DI17AH, BIT 12 THROUGH 17

SN2 SHIFT 15 IN H

SN2 SHIFT 17 IN H

THE 18 DATA LINES FROM THESE PCBs ARE: TDO DIOOBH-TDO DI05BH, BIT 00 THROUGH 05
TEO DI06BH-TEO Dl11BH, BIT 06 THROUGH 11
TFO DI12BH--TFO DI17BH, BIT 12 THROUGH 17

DESIGNATOR IN BOX (c:::J) INDICATES CORRESPONDING PRINT SET DR~WING

BITS 00-07 (SN3 BUFOOH - SN3 BUF07H) ARE TAKEN THROUGH THE SYNC BYTE
MULTIPLEXER FOR APPLICATION TO THE I/O DATA SHIFT REGISTER

Ir--------{ d
I SN6/SN 2 1

RG 1 22 FORMAT H _

READ

SN1 HEADER ENABLE (1 ) L -

GATING

SN 1 SYNC. STROBE (1) H -

LOGIC
SN1 READ ENABLE DISK H -

r---

TD!/l 0100 BH
(SEE NOTE 2)
FROM CONTROllER B
DRIVE TRANSCEIVER
PCBs
(MASS BUS
INTER FACE)

{ •
t

18 LINES

MA0 RD/WRT DATA H

TFfZJ017 BH
(SEE NOTE 2 )

(-PART OF

TA0 DI
(SEE NOTE 3)
00AH
( SEE
NOTE 1 )

I
I
I

CONTROllER 'A
DRIVE
TRANSCEIVER

I
18
LINES

PCBs

FROM
MASS
BUS

IEC91

(Iv'ASS BUS

INTERFACE )

I
I

EC9
DA00H

!SN31
SN3 BUF 17 H

(SEE NOTE 3)

r-----------.----b----------------~e

t
I

I
I

DATA INPUT

MUX

18
LINES
i

I
I

I
I
I

~
TCfZ) D1 17 AH
(SEE NOTE 1 )

I
I
I

DATA
81JI'"FER

18 LINES

I
I
SN3 BUF
f---+ 07 H (SEE
NOTE 4)

I
I
I
I

~----------~--~----------------~f

EC9 DA17 H

SN3 BUF 00H
(SEE NOTE 4)

PARITY
~

RUN

DP5 PORT B2 ON H

SN1 READ
ENABLE l

SN4 BUF ClK l

'--------®
! !-24?OA

Figure 2-4 Synchronous Data Transfer Path
Block Diagram (Sheet 1 of 2)

2-30

a
b

ISN3!
(SEE NOTE 3)

SN3
SR17H

I
I
I

SHIFT

18 LINES
I

I
I

8 LTES

SN3 SR00H

I I 5021••,T f

lENA H
.....
SN0 LOAD _
SR H

EC0 SHIFT
CLK.H

SN0 SHIFT
CLR L

I I

I fSN2l

;

PART OF

I
I

(SEE NOTE 3)
SYNC
CHARACTER
MUX

SNO WRT SYNC L

I I

8UF~L

! SN2!

I I

I SN2

(SEE NOTE 3)

SN3 BUF
07 H

CONTROLLER A

OUTPUT
INVERTERS

DRIVE

I
I
18 LINES
!
I

TRANSCEIVER
PCBs

I
I

•

SN2 BUF 17 L

SN3 SR 00H

SS7 CRC IN L
SNl/J WRT OR H

TO MASS BUS

I
I
I

EC3 SHIFT IN L _ _

T CONTROLLER B
DRIVE TRANSCEIVER
PCBs
( MASS BUS INTERFACE)

(MASS BUS
INTERFACE)

J
- ----..r--

I SN21
(SEE NOTE 3)
WRITE GATING
LOGIC
SN2 RD/WRT DATA H

ISN 61
PHASE
SET-UP

SN7 SHIFT CLK L - - FLIP-FLOP

SN6 R/W DT
LEVEL (1) H

MA(1l
(SEE NOTE 3)

1-(+) READI WRITE DATA LE

VEL}

TO I FROM DISK

1-(-) READI WRITE DATA LE VEL

MINIMUM
DEVICE
LEVEL

MA!1J RD I WRT DATA H

INTERFACE
(MDLl )
11- 24708

Figure 2-4 Synchronous Data Transfer Path
Block Diagram (Sheet 2 of 2)

2-31

•

In response to the Bus Sync Clock, the controller echoes back a write clock signal which the DeL uses to
develop signal SN4 BUF CLK L.

From the data buffer register, the 18/ I6-bit word is entered (in parallel) into the shift register.
NOTE
The 8 low order bits are taken through a sync character
multiplexer circuit for application to the shift register.
At times, it is necessary to write sync bytes as part of
the sector format (see discussion on sector format).
The SNO WRITE SYNC L signal is used to enable transfer of sync characters through the sync character multiplexer
for application at the 8 low order bit positions of the shift register.
Signal SNO LOAD SR H is used to allow transfer of data words being parallel loaded into the shift register. Since the
DCL is capable of writing both 16 and 18-bit words onto the disk, the time that loading occurs depends on'the word
length. In other words, if an I8-bit word is being written, 18 shift pulses must occur (for writing each bit onto the
disk) before an SNO LOAD SR H signal is issued. For 16·bit words, only 16 shift pulses need occur before SNO
LOAD SR H is asserted. Once a word is loaded, it is shifted out (one-bit at a time) via the least Significant bit line
(SN3 SR 00 H). Shifting is affected by the ECO SHFT CLK H signal which is derived from the PLO clock supplied
from the disk. Two additional signals used by I/O data shift register during write operations are:

SN2 18 BIT ENA H. This is used to enable the two high order bits of the register that are only operative
during I8-bit transfers.

SNO SHFT CLR L. This is used to clear out the register (at the start of each sector and at ot~er times)
when it is necessary to write zeros onto the disk. See discussion on sector format.

Each bit shifted out of the shift register is taken through the write gating logic for application to the phase setup
flip-flop. Since a write operation is being performed, signal SNO WRITE OR H is asserted to allow each bi~ from the
shift register to pass through the write gating logic. The purposes of the two remaining signals applied here are:
1.

SS7 CRC IN L. This is used to write the CRC word produced as part of the header format. (See sector
format discussion.)

EC3 SHIFT IN L. This is used to write the lECC field fo])owing the data field. (See sectpr format
discussion.)

The phase setup flip-flop is set/reset consistent with each ONE/ZERO supplied from the write gating [:ogic. This
flip-flop is clocked by the SN7 SHIFT CLK L signal which ensures that setting/resetting (and eventual flux reversal
on the disk surface) occurs during the middle of the bit transfer time.
From the phase setup flip-flop, the signal (SN6 R/WDT LEVEL (I) H) is taken to a differential line drjver in the
MDLI circuits. In turn, the signal is issued over the read/write data level lines to the disk circuitry.
2.4.2.2 Read Operation (Disk-to-Massbus Transfers) - Data words coming from the disk travel through the
following circuits before being sent over the Massbus:
1.

MDLI circuits

Read gating logic

Shift register

2-J2

Data buffer register

Output inverters

Controller A/controller B drive transceivers PCB's

Data bits read from the disk are firslt taken through a differential line receiver in the MDLI circuits and applied to the
read gating circuits as signal MAO RD/WRT DATA H. Since a read operation is in process, signal SNI READ
ENABLE DSK H is asserted.. This allows data read from the disk to be shifted serial1y to the shift register.
Application of the received data to the shift register can be over one of two lines, SN2 SHIFT 15 H or SN2 SHIFT
17 H. The former is used when receiving 16-bit words and the latter when receiving 18-bit words. Certain control
signals are applied to the read gating logic to govern the time, at which a particular output line is selected. These
signals and their uses are:

RG 1 22 FORMAT H. This signal is asserted as long as bit 12 of the offset register is set. It means that
the device control logic is operating in the 16-bit mode and causes selection of the SN2 SHIFT 15 H line
as the input to the shift register.

SNI HEADER ENABLE. Regardless of operating mode (16 or 18-bit) the header is always in 16-bit
format. This signa.l enables transfer of 16-bit header information over the SN2 SHIFT 15 IN H line when
the device control logic is being operated in the 18-bit mode.

SNI SYNC STROBE H. As mentioned earlier, the sync byte is always positioned in the low order
character position of a 16-bit word. Consequently ~ when the sync byte is being read it must be inserted
in the register over the SN2 SHFT 15 IN H line and then shifted into position for detection.

If the device control logic is in the I8-bit mode, signal SN2 18 BIT ENA H is asserted. Essentially, this signal extends
the I/O data shift register two more bits. The most significant bit position of the shift register receives the SN2
SHIFT 17 IN H signal from the read gating logic. After 18 shift pulses the word is properly positioned for transfer to
the data buffer register. Transfer is over the lines designated. SN3 SR 00 H through SN3 SR 17 H.
Since a read. operation is in process, signal SNI READ ENABLE L is asserted., allowing the data buffer register to
accept the inputs from the shift register rather than the data input multiplexer. Strobing of the word into this
register is affected by SN4 BUF CLK L. After a word is completely assembled in the shift register, signal SN4 BUF
CLK L (produced as a result of the number of shift pulses required, i.e., 16/18) is asserted to parallel load the data
buffer register.
Output signals SN3 BUF 001 L through SN3 BUF 17 H from the data buffer register are taken through a set of
output inverters for application to the Massbus interface circuits.
2.4.3 Basic Clock and Index Pulse Distribution
Numerous control operations: within the DCL are governed in one way or another by the clock and index signals
supplied from the drive. Figure 2-5 shows the distribution and key uses made of these signals within the DCL.
2.4.3.1

Basic Clock Signals -- Two basic clock signals are suppJied from the drive logic:
PLO CLOCK - The phase locked oscillator (PLO) signal is taken through a line receiver in the MDLI
interface logic and applied to a three level synchronization network on the error correction PCB. Here it
is used to implement and synchronize all control sequences required during all operations other than
read activities.

2-33

r-__~S_N_1_S~Y_N~C~Cl~K~T~IM~E~(~O~)~H____-1a

IERROR CORRECTIONLOGIC- -

MBl
MBl PLO ClK H

PlO CLOCK

ECO

3 lEVEL

SNYC NETWORK

1-------------------------------------------------------------------------:---..

{ (PHASE lOCKED
OSCilLATOR SIGNAL)

~~ --SNI SYNC

rM
__
Bl__
RE_A_D__
sT_R_O_B_E_H__________________________________________________________________
I~~---------~

READ DATA STROBE

~~~

RING
COUNTER

L - -_ _

-1

EC0 SHFT ClK H

I
--=-cc--

EC5 WORD INH
-

-------

- -

----

'------~

~CLD~C~K~E~N~H~~~-------~~E=00~B~US~SY~N~C~C~~~lj
SYNC
CLOCK
GENERATOR
CIRCUITS

ECO WRITE STROBE H

EC0 SYNC ClK l
ECIl> BIT 0 H
EC0 BYTE ClK H

L~READ~BlEH_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .-J

{WRITE DATA STROBE

IssLOGiC"" - I
I

MAO

DRIVE

SSB BYTE CNT ( 1) H

~
~

BYTE
COUNTER

20 ~ NES

SS~ BYTE CNT 512 H

L-- ___ ..J
SN6 BYTE CNT ClR l

IPARTOFSNLOGIC-

--1

CLEAR BYTE
COUNTER
CONTROL

~--------------------------~--~+_--_4f

I
I Is S( SECTOR SEARCH ')'LOGIC I

L _______ -.J

--l

SECTOR FOUND

CONTROL AND

IoUAL CONTROLLER (DP )lOGIC- MBl SECTOR ClK H

MB'
INDEX PULSE

I
MBl INDEX PULSE H

SECTOR
CLOCK
(01 BIT)
COUNTER

FLI P-FLOP

DP6 SECTOR PULSE

(1) H

SECTOR
COUNTER

I DP6 SECT CNT 00 (1) H

SS5 SECTOR COMP H

5 LINES

I DP6 SECT CNT 04 H

_ _ _ _ _ _ _ _ _ _ _ _ _ -I

~-+----{g

-+-___-{ h

L....-_ _

SS0 SECTOR[ENABlES
HEADER
FOU NO (1) H SEARCH I
HANDLING
I
lOGIC

DP0 C00 AB

1----7--~~.:..:...:.-::..:....:.:..:....----:--1- t

i 1L-==:=====------11
L

+---------...!--------------------------.-I SECTOR FOUND

--I

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

FROM [SECTOR CLOCK
DRIVE

-- --

I
I

SECTOR
COMPARE

5 LINES

DESIRED
SECTOR
REGISTER

DP0 C04 AB

L _ _ _ _ _ _ _ _ _ _ _ _ --.J

11-2471A

Figure 2-5 Basic Clock and Index Pulse Distribution
Block Diagram (Sheet 1 of 2)

2-34

ar---------------------------------------------------------------------------~

®~---------------. TO SHIFT REGISTER

----,

Cr---------------------------------------------------------------------------~~------------------~--+E00BUSSYNCClKl
(TO CONTROllERS
A e. B)
~-----------------I

SN LOGIC

SN8 BYTE 00 (00) H
SN8 BYTE 02 (02) l

SYNC
CLOCK
TIME
FLlP- FLOP
(SN1)

SN8 BYTE 04 (04) l

SN8 BYTE 05 (05) H
SN8 BYTE 06 (06) H

USED TO
IMPLEMENT READING.
WRITING OF
VARIOUS SECTOR
ELEMENTS

SN8 BYTE 08 (10) H
SN8 BYTE 09 (1 t) H

BYTE COUNT
SHIFT REGISTER

I
e

SN8 BYTE 10(12) H

sNS 8YTI; 11 (13) H

•

SN8 BYTE 15 (17)H
SN8 EOB BYTE H (512F + 576 F )
SN8 END ECC BYTE H

-I

- )

SN8 EOB W BYTE H (518F + 582 F)

SN5 EBl l

END- OF-BLOCK SN5 EBl l
GENERtIJOR

rsN8 BYTE 511/575 H

~NA our
........ '''v.~
"' ..."'...
PART OF
r--

;:)1

BYTE COUNT
DECODE
lOGIC

SN8 BYTE 39 (47) H

} USED FOR SYNC
BYTE WRITING I
SN8 BYTE 26 (32) H

DETECTION

DATA BUFFER

PARITY CHECKER
AND GENERtIJOR
lOGIC

f-- } TO

f----

SHIFT
REG

r--

I
EC0 SYNC ClK l
EC5 WOR IN H
SYNC
ClOCK ENABLE
SN0 SEND HEADER l
CONTROL
- - - - - - - - : - - + 1 AND SYNC ClK
ENABLE
SNI READ SECTOR (l)H
FLIP-FLOP

SN I READ BUF ClK l

SN8 WRITE
ClK H

WRITE CLOCK
SELECT lOGIC

TA0 WRT ClK AH}

SNI SYNC CLl< EN H

I
I TD0 WRT ClK B H

SN0WRITEORJ-------------------------~

FROM
CONTROLLERS

I
11-24718

Figure 2-5 Basic Clock and Index Pulse Distribution
Block Diagram (Sheet 2 of 2)

2-35

READ DATA STROBE - This signal is also taken through the MDLI interface logic and applied to the
three level synchronization logic. It is used to implement the control and transfer sequence during read
operations (read header and data, read data and the header handling portion of the write data
operation).

Each of these clock signals is used within the three level synchronization network to generate ECO SHFT CLK H.
Signal SNI READ ENABLE H (suppJied from the synchIOnous logic and asserted during read operations) is used to
select MBI READ STROBE H as the source signal to produce ECO SHFT CLK H. When SNI READ ENABLE His
not asserted, meaning no read operations are in process, then MBI PLO CLK H is selected as the clock source signal.
The ECO WRITE STROBE H signa] (generated by dividing the PLO clock signal in half) is used by the Drive to write
the data bits onto the disk. One purpose of the ECO SHFT CLK H signal during write operations is that it shifts bits
serially out of the shift register for transfer to the Drive. Therefore both shifting of the data bits and the
accompanying write strobes are under control of the MBI PLO CLK H signa1.
2.4.3.2 Sync Clock Generator Circuits - The sync clo,;k generator circuits consist of a shift register and an
end-around counter both of which are clocked by the ECO SHFT CLK H signal. The shift register is used primarily
for developing the sync clock signals used in synchronous data transfers while the end-around counter serves chiefly
to count bits to develop a byte clock. Four output signals are produced by the sync dock generator circuits. These
signals and their system uses are described in the paragraphs below.
•

Signal ECO BUS SYNC CLK L - This signal is shipped to the controller for each synchronous word
transfer between controller and DCL, i.e., whether it be a header word or data word. Signal SNI SYNC
CLK EN H controls the times at which the ECO BUS SYNC CLK L signal is sent to the control1er. By
asserting SNI SYNC CLK EN H (supplied from the SYNC CLK ENABLE flip-flop in the SN logic) four
times during each header field transfer and 256 times during each data field transfer, the number of
SYNC CLOCKs required for a complete sector transfer are developed.

•

Signal ECO SYNC CLK L - This signal switch es high at the trailing edge of ECO BUS SYNC CLK Land
is used to clear the SYNC CLK ENABLE flip-flop. Since the data word (for both read and write
operation) is now in the data buffer register, the SYNC CLK ENABLE flip-flop is cleared until it is time
to generate the sync clock for the next header/data word.
NOTE
Setting the SYNC CLK ENABLE flip-flop is under
control of the ring countl~r which is clocked by the ECO
SHIFT CLK H pulse. By counting the number of shift
pulses necessary to shift a word out of the shift register
(write) or into the shift register (read), the ring counter
determines when the DCL is ready to receive/send
another word. At the appropriate time, then, the ring
counter asserts EC5 WORD IN H to set the SYNC CLK
ENABLE flip-flop.

•

Signal ECO BIT 0 H - This signal is used in the SN logic to insert the header gap sync character into the
shift register.

•

Signal ECO BYTE CLK H - This signa] is used to clock the byte counter and to provide the shift pulses
for the byte count shift register. Both of these circuits are used to implement the various control
functions during read/write operations. This signal is also used to develop a decode strobe within the
byte count decode logic.

2-36

2.4.3.3 Ring Counter - The ring ,counter is clocked by the same signal used to clock the sync clock generator (ECO
SHIFT CLK H) and to shift bits through the shift register (Figure 2-4). This counter is enabled only for the span of
time when sync clock signals are to b~~ issued to the control1er; that is, for header and data fields (see discussion of
sector format). The times at which this counter is enabled are governed by the "sync clock time" flip-flop in the SN
logic. That is, signal SNI SYNC eLK TIME (0) L must be asserted. When enabled, the ring counter counts the
number of bits shifted out of the shift register (write) or into the shift register (read). By asserting signal EC5 WORD
IN H when a word is funy assembh~d in the shift register, the ring counter determines when it is time to send/receive
a new word. Signal EC5 WORD IN H is used to set the "sync clk enable" flip-flop in the SN logic. The latter circuit
enables generation of the sync clock to the controller as described earlier.
2.4.3.4 Byte Counter and Byte Count Shift Register - The byte counter and byte count shift register keep track of
the synchronous timing throughout the entire sector. In doing so, they provide the necessary timing signals for
reading and writing bytes/words as demanded by the various sector fields (see sector format discussion). Both
circuits are cleared at the start of each sector by SN6 BYTE CNT CLR L. They are also cleared at other times during
a sector such as at the start of the header and data fields.

NOTE
By preS{~tting the least significant bit of the byte count shift
register to a one count and then shifting it through higher
order bit positions (on each ECO BYTE CLK), the result is
effectively the same as counting bytes. Use of the byte count
shift registe:r minimizes the amount of logic required for
decoding byte counts if the byte~ counter was used alone.
All outputs necessary for writing/readIng the various sector elements are supplied from the byte count shift register
and byte count decoder. The byte count decode logic is used to detect certain specific byte counts of the byte
counter. Two of these are:
1.

Signal SN8 BYTE 30 (36) Hand SN8 BYTE 39 (47) H are used in writing/detection of the sector sync
bytes. (See sector format discussion.)

Signal SN8 BYTE 511/575 H is decoded to detect the end of the data field.

The latter signal is applied to the byte count shift register and after being shifted seven times, it produces SN8 EOB
W BYTE H. This is used to generate the: end-of-block signal to the controller.
2.4.3.S Sync Clock Enable Control and Sync Clock Enable Flip-Flop - As mentioned in the discussion of the sync
clock generator circuits, the sync clk enable flip-flop controls the times at which the ECO BUS SYNC CLK L signal is
gated out to the controller. This flip-flop is preset by EC5 WORD IN H from the ring counter and clocked reset by
ECO SYNC CLK L occurring at th~~ trailing edge of the sync clock signal sent to the control1er. However, the sync
clk enable flip-flop can only be set at certain times as governed by the following signals:
1.

SNO WRITE OR H - This allows the sync clk enable flip-flop to be clocked set at the fo]]owing times:
a.

During the first four words of the header field when executing a write header and data command
(formatting).

During each word of the data field of both the write header and data command and the write data
command.

2-37

SNI READ SECTOR - This allows the sync elk enable flip-flop to be clocked set for each data field
word during both the read header and data command and the read command.

SNO SEND HEADER L - This allows the sync clk enable flip-flop to be preset during all commands
requiring reading of the header. However, addiltional gating in the sync clock generator circuits inhibits
issuance of ECO BUS SYNC CLK L during the header field except when the write header and data and
read-header and data command are being executed.

2.4.3.6 Sector Clock Counter and Sector Counter - The DCL employs a special counter to develop se¢tor pulses
because the disk can operate with formats of 20 or 22 sectors. To develop the sector pulse at the proper time (i.e.,
consistent with the number of sectors involved), the sector clock counter counts a fixed number of di-bits (issued
from the disk itself and applied as MBI SECTOR CLK H) bl~fore issuing the sector pulse (DP6 FUNC SECT CLK H).
If the 22 sector format is being used, the sector clock counter counts 609 di-bit pulses before issuing the sector
pulse. In the 20 sector format, it counts 672.
The sector counter itself provides two basic outputs:
1.

DP6 SECTOR PULSE (1) H - This is issued every sector and is used to clear out the byte counter/byte
counter shift register and to clock the sector found flip-flop.

DP6 SECT CNT 00 (1) H through DP6 SECT CNT 04 H - These five lines convey the current sector
count to the sector compare logic.

2.4.3.7 Sector Compare Logic and Desired Sector Register - The sector compare logic detects a match btHween the
current sector and the desired sector addressed by the controller. Detection of this matchup means that the
particular sector addressed by the controller has been found. The sector compare circuit compares inputs from the
sector counter (current sector count) and the desired sector register (sector addressed by contro]]er). When the count
from the sector counter matches that from the desired sector register, signal SSS SECTOR COMP H is issued.
2.4.3.8 Sector Found Control and Sector Found Flip-Flop - These circuits detect the sector found condition when
the sector matchup occurs. At this time, the sector found flip-flop issues signal SSO SECTOR FOUND (1) H to
enable the header handling logic for the header compare process.
2.4.4 Sector Format and Related Control/Synchronization Requirements
Figure 2-6 shows the component elements that make up an entire sector in the 16-bit format. It is important to
understand the positioning and structure of the various format byte/word elements, since such understanding
provides insight into the control sequence and synching requirements necessary for the type of operation being
performed. When a disk is being formatted through use of the write header and data command, the elements shown
in Figure 2-6 must be written onto the disk. When simply writing data onto or reading from the disk, detection of
sync bytes, cylinder address, and verification of the header information must precede the actual data fielid transfer.
The entire sector consists of 609 8-bit bytes in the 16-bit format. Even when the data field contains 18-bit word (in
cases where the Drive is used with the DECsystem-l0) all words preceding and after the data field are in 16-bit
fo ml at.
The following breakdown describes the makeup of each sector beginning with the pre-header/sync field occurring
immedia tely after the sector pulse:
1.

Prc-header/sync field. This is a 20 word/40 byte field. It has 39 bytes of zeros fol1owed by a sync byte
(IOOI 10002 ). The latter defines the start of valid information.

2-38

SECTOR PULSES

AA A A AA A A A" A
~~~----"--,\I'9 \20 I 21 I

INDEX PULSE -

5
20 WORDS

PRE - HEADER SYNC
39 BYTES OF ZEROS

PULSE

IA\

/
5

10011000 (SYNC BYTE)
DESIRED CYLINDER ADDRESS AND
FORMAT BIT

(512 BYTES)
SEE NOTE 4

HEADER GAP

WORD WORD WORD WORD
2
3
4
5
16 BITS 16BITS 16BITS 16BITS 16BITS
WORD

O' ·········000·····0

256 WORDS

WORDS

HEADER FIELD

1 BYTE SYNC (S i

SECTOR

)

0---00 ~
r-

DATA FIELD

WORD

WORD WORD

WORD

WORD
254

WORD WORD
255

WORD
2

0 ••• 0

UNRECORDED SPACE EQUIVALENT
TO 2B BYTES

IA\ -

SECTOR PULSE
(NEXT SECTOR)

11 BYTES OF ZEROS1

2 BYTES OF ZEROS
10011000( SYNC BYTE)

DESIRED SECTOR I TRACK ADDRESS

KEY FIELD .# 1

KEY FIELD .:# 2
HEADER eRC

WORD

NOTES:
1. ONE WORD: 16 BITS: 2 BYTES.
2. ONE BYTE: 8 BITS.
3. TOTAL NUMBER OF BYTES PER SECTOR: 60S BYTES.
4. FOR IS- BIT FORMAT DATA FIELD CONTAINS 576
BYTE RESULTING IN A TOTAL OF 672 BYTES PER
SECTOR.

11- 2472

Figure 2-6 Sector Format (16 Bit Mode) Diagram

2-39

Header Field. This consists of five words whose content is described below:
Word I - Cylinder address and format bile used to specify anyone of the addressable cylinders on
the disk (411 for an RP05; 815 for an RP06). A format bit may be set (under software control) to
specify the 16-bit format.
Word 2 - Sector/Track Address used to specify anyone of 19 tracks per cylinder and anyone of
20/22 sectors per track depending on format. Bits 0-4 of the low order byte specify sector
address while bits 8-12 of the upper byte indicate track address.
Words 3 and 4 - Key field I and 2 respectively are available for programming use and have no
bearing on control operations within the DeL.
Word 5 - Cyclic Redundancy Check (CRC) word for header. This is generated by the DCL and
then written onto the disk when formatting. It is checked by the DCL when reading from the disk
to establish the accuracy of the header field content.

Header Gap is a 6 word/12 byte field that consists of 11 bytes of zeros followed by a sync byte. This
allows time for CRC checking and to determine that a sector identification has been made when reading
from the disk. The sync byte is inserted, as befOIe, to define the start of valid information.

Data Field allows for writing up to 256 words of data. This is true in either 16-bit or 18-bit format. The
additional space consumed in the 18-bit mode results from the fact that there are only 20 addressable
sectors per track as opposed to the 22 sectors available in the 16-bit mode.

Error Correction Code (ECC) Field. Two words of error correction code are required due to the length
of the polynomial used in the error correction process. These are generated during write operations, and
are read and checked during read operations.

Data Gap. Two bytes of zeros are inserted after the ECC field to ensure a clean break between ECC data
and the tolerance gap and to compensate for the timing differences between the DCL and the Drive.

Tolerance Gap consists oC14 words (28 bytes) equivalent to 34.72 microseconds. It is insert~d here to
compensate for mechanical tolerances.

For each element (field) making up the format, certain control sequences are required. Moreover, the control
sequence implemented in the DCL can vary depending on whether the operation called for involves formatting,
writing, or reading data. Table 2-2 attempts to point out some of the more salient sync and control requirements
implemented during each field, consistent with the type of operation being performed; that is, formaHing (write
header and data), writing data only, reading header and data, and reading data only.
2.4.5 Disk Addressing Logic, Block Diagram Discussion
Figure 2-7 is a block diagram of the DCL circuits used to address and compare cylinders, tracks, and sectors on the
disk. Cylinder addressing is effected when: the controller executes a seek command; the implied seek condition
occurs as a result of the controller executing any read/write command; or the cylinder address is updated during an
extended read/write.
Sector/track addressing is effected as part of any read/write or search command. Even though no mechanical
movement of the read/write heads may be required (heads. already positioned) sector/track address information is
essential to the header formatting or header identification process.
Sector addressing may also be effected on execution of the search command by the controller; tha~ is, under
conditions where the operating system is cognizant that the proper cylinder (seek complete) and track have already
been selected and need only be informed when the addressed sector passes under the heads.
2-40

Table 2-2
SECTOR FORMAT PROCESSING FOR READ/WRITE COMMANDS
WRITE HEADER A..~D DATA, 63 8

SECTOR FORMAT
ELEMENT
Sector Pulse

WRITE DATA, 618

READ HEADER AND DATA, 73 8

READ DATA, 718

Same as write data

(FORMATTING)
Clocks sector counter to current sector address

Clocks sector counter to current sector address

Clear data shift register to ensure writing of ZEROs

Provides sector compare at addressed sector

onto disk. Clear Byte Counter prior to beginning
byte count.

Clears shift register

Sets sector-found and format command flip-flops

Clears Byte counter prior to beginning byte

meaning ttl",t the sector to be formatted has been

counter

found.
Sets the sector found flip·flop (when sector
count equals desired sector address) as precondition to initiating the header compare
process.

Pre-Header Field

Sync clock signal (ECO BUS SYNC ClK l) is sent

Byte Count of 30 sets read enable flip-flop

to Controller informing it that DCl is ready to

(SNI READ ENABLE H) and sync strobe flip-

accept 1st header word.

flop to prepare DCl logic for sync byte de-

Controller responds with write clock (TAO WRT

tection and to enable reading of header words
from disk.

ClK A HI to indicate that the first header word is
on the data lines. First header word is strobed into

Detection of sync byte indicates that DCl

the data buffer register.

is now looking at header field (SSO

Same as write data

HEADER AREA (11 H flip-flop is setl
Zeros are written onto disk until byte counter
counts to 39. At this time sync byte multiplexer

Detection of sync byte also clears byte

is enabled to insert sync byte into sh ift register

counter.

for writing onto disk. DCl is now prepared to
accept header from controller.

loading of sync byte in shift register also clears
byte counter.

During byte count of 39, DCl initiates the follow·
ing.

1. DCl producesSN4 BUF ClK l signal to enter first header word into data buffer register.

Table 2-2 (Cont)
SECTOR FORMAT PROCESSING FOR READ/WRITE COMMANDS
SECTOR FORMAT
ELEMENT

WRITE HEADER AND DATA, 63 8
(FORMATTING)

WRITE DATA, 618

READ HEADER AND DATA, 73 8

READ DATA, 71,

Same as write data

2. Sync byte is shifted out of shift register
and written onto disk in the byte 39

(Cont)

position.

3. After sync byte is shifted out of shift
register, first header word is loaded
into shift register by SNO lOAD SR H
Header Field
1. Cyl. Addr.

Sync clock signal is generated to controller

First header word (current cylinder address) is

Same as write data except that sync

which in turn responds with write clock to
enter second header word into data buffer
register.

read from disk into shift register and then
clocked into data buffer register.

clock (ECO BUS SYNC ClK l) is
asserted to send each of the four
header words to controller.

Cylinder address is shifted out of shift
register and written onto disk as first

desired cylinder address are compared at byte
count of 02. If match exists, SSO CYl MATCH

header word.

l signal is asserted.

2. SectJFrk

Sync Clock signal is generated to controller

Second header word (sector/track address) is

Addr

which responds with write clock to enter third
header word into data buffer register (see dis-

read from disk into shift register and then
clocked into data buffer register.

First header word (current cylinder address) and

cussion under pre-header field).
Second header word (current sector/track adSector/track address is shifted out of shift

dress) is compared with desired sector/track

address at byte count of 04. If match exists,
signal SSO All MATCH l is asserted.

3,4 Key Field

Sync clock signal is sent to controller to

Key fields are successively read from disk for

words

in itiate process for entering fourth header

entry into shift register followed by entry into

word into data buffer register.

data buffer register. However they are not
sampled and acted upon by DCl logic.

Third header word (now in shift register) is
sh ifted out and written onto disk after which

the 4th header word is strobed into shift register and then shifted out for writing onto disk.

Same as write data

Table 2-2 (Cant)
SECTOR FORMAT PROCESSING FOR READ/WRITE COMMANDS
SECTOR FORMAT

WRITE HEADER AND DAT A, 63 8

WRITE DATA, 61b

READ HEADER AND DATA, 73 8

READ DATA, 718

(FOR.MA TIING)

ELEMENT
(cont)
5. CRC word

CRC word (generated during the 1st four words

CRC word from disk is clocked into CRC logic

Same as write data except header found

of the header field) is now written onto disk as

for CRC check. If error, HCRC bit in error

flip-flop is set at byte count of 10 even

fifth header word (this word does not go

though CRC error occurs.

through the shift register).

flip-flop iSSO HEADER FOUND (1 i Hi is set.

Same as write data

Header Ga p

Byte COllnt 10

Clears read eanble flip-flop (SN1 READ EN·

Clears the read enable flip-flop but only

Same as read head.-

ABLE HI since the header identification has

temporarily as this flip-flop is again set

and data

been made and no further word need be read

later on in the header gap.

from the disk as part of the write command
operation.
Byte Count 11

Clears sh itt register so that zeros are written

Resets header area flip-flop since all header

onto disk for remainder of header gap

words have now been read from disk (signal

(SNO SHFT CLR LI.

SSO SEARCH RESET L c!ocksSSO HEADER

Same as write data

Clears header enable flip-flop (SN 1

Same as read header

HEADER ENABLE (1) H since all

and data

AREA (1) H flip-flop resetl.
First byte clock pulse after trailing edge of
SN8 BYTE 11 (13) H signal clears and presets

CiearsSN1 HEADER ENABLE (1) H flip-flop.

byte counter shift register (this is done in anticipation of writing the sync byte at the end of
the header gap).

First byte clock pulse after trailing edge of SN8
BYTE 11 (131 H signal clears and presets byte
count shift register. This is done in anticipa-

Sync clock signal is sent to controller informing

tion of writing sync byte at end of header gap.

it to send first data field word. Controller responds with write clock wh ich enters first data
word in data buffer register.
Byte Count 15 4

header information has already been
sampled for both read commands.
Sets read enable fl ip-flop

• Used during read operations only.

Table 2-2 (Cont)
SECTOR FORMAT PROCESSING FOR READ/WRITE COMMANDS

WRITE HEADER AND DATA, 63 8
(FORMATTING)

SECTOR FORMAT
ELEMENT

WRITE DATA, 618

READ DATA, 718

READ HEADER AND DATA, 73 8

(Cont)
Sets read sector flip-flop (SN 1 READ

Same as read header

SECTOR (1) H.

and data

Jam presets sync strObe flip-flop (SN 1

Same as read header

SYNC STROBE (1) H) in anticipation

and data

of detecting sync byte at end of header
gap.
Same as write header and data

Sync byte multiplexer is enabled to insert sync

Byte Count OS·
(Byte Count 21)

into 8 low order bits of shift register (SNO
WRITE SYNC l)

Same as read header

detected indicating that the DCl is

and data

now ready to receive the data field.

Sync byte is read into shift register and

Sync byte is written onto disk.

Same as write header and data

Data envelope flip-flop is set to indicate data

Same as write header and data

Data envelope flip-flop is set to indicate

field and to initiate generation of the error

data field and to initiate generation of

correction code.

the error correction code.

First data word is entered into shift register for

Same as write header and data

writing onto disk.

Same as read header
and data

Byte counter and byte count shift regis-

Same as read header

ter are cleared

and data

First data word is shifted into shift reg-

Same as read header
and data

DATA FIELD
Word 1

First data word is shifted out of shift register
for writing onto disk.

Same as write header and data

ister and when fully assembled in the
shift register (EC5 WORD IN H) the

Sync clock signal is sent to controller informing

word is strobed into data buffer register.

it to send next word etc.

The Del now generates the sync clock
(ECO BUS SYNC ClK l) to the controller informing it to take the word in the
data buffer register.
Once the first data word is strobed into
data buffer register, the second data
word is shifted into shift register etc.

·Since the byte count shift register was cleared and preset at byte 11 time (i.e., at a time that defines the twelfth byte following the first header word) the byte count of OS occurs after byte count 15
and for write operations defines the time that the sync byte is to be written on the disk.

Table 2-2 (Cont)
SECTOR FORMAT PROCESSING FOR READ/WRITE COMMANDS
WRITE DATA, 61~

WRITE HEADER A."lD DATA, 63"

SECTOR FORMAT

READ HEADER AND DATA, 73 8

READ DATA, 718

(FORMA TII:-.IG)

ELEMENT
DATA FIELD
(Cont)

Same as write header and data

Last data field word is shifted out of sh ift

Word 256

Data envelope flip-flop is now reset (SN 7 DATA
ENVELOPE (1) H) and ECC envelope flip-flop
is set (ECC ENVELOPE (1) HI.
SYNC CL K TI ME (1) H flip-flop is cleared since

I Same as write header and data

I
II

Last data word is shifted into shift

and data

Same as write header and data

no more sync clock pulses are to be sent to the
controller (SN8 EOB BYTE HI.
I

ECC Field

I
I

The two ECC residue words are taken from the

Last byte of data field (byte 512, EOS

Same as read header

byte is detected by byte count decoder.

and data

Data envelope flip-flop is reset and ECC

Same as read header

envelope flip-flop is set.

and data

The two ECC words are checked to de-

Same as read header

tect any error condition.

and data

Same as write header and data

error correction logic and written into the disk.
Signal SN8 END ECC BYTE H is now generated

Same as read header

Same as write header and data

Signal SN8 END ECC BYTE H is now
generated to clear the ECC envelope

to clear the ECC envelope flip-flop.

flip-flop.

Data Gap

At the end of the data gap, signal SN8 EOB W
BYTE H is generated to effect the following

Same as write header and data

At the end of the ECC field, the byte

Same as read header

count shift register produces SN8 EOB

and data

W BYTE H to effect the following
1. Reset the write sector flip-flop (SNO
WRITE SECTOR (1) H

1. Develop signal SN5 END ECC GTL
to clear the read sector flip-flop (SN 1

2. Trigger the end-of-block one shot multi-

READ SECTOR (1) H)

vibrator that issues the end-of-block signal
to the controller (SN5 EBL (1) H l.

2. Triggers the end-of-block one shot
multivibrator that issues the end

Table 2-2 (Cont)
SECTOR FORMAT PROCESSING FOR READ/WRITE COMMANDS
SECTOR FORMAT
ELEMENT
Data Gap iCont}

WRITE HEADER AND DATA, 63 8

WRITE DATA, 618

READ HEADER AND DATA, 73 8

READ DATA, 718

(FORMATTING)
3. Clears sector area flip-flop (SN5 SECTOR

of block signal to the countroller
(SN5 EBL (1) H).

AREA (1) HI.

3. Clears sector area flip-flop (SN5
SECTOR AREA (1) HI.
Tolerance Gap
(14 words)

No action

RG3 GOO H
RG5 DES CYL
ADR SEL L
~---------------- SS2 CYL DIR H

RG 5 WRT REG L - - - - ' .
DP0 E00 AB

- - - - - - - , - - - - + 1 DESIRED CYLINDER
SEE
NOTE

ADDRESS

10 LI'NES

(DCA)

S51 DCA 00 HS51 DCA 09 H

SS1 DCA 0¢ HSS1 DCA 09 H

(SS1 )

DP0 TC!l9AB

SS2 CYL DIF 00 H

10 LINES

SS1 CCA 00 L
SS1 CCA 09 L

5S5 CYL COMP H

CYLINDER

SS3 CLR TRK H

CYLINDER
ADDRESS

CURRENT
CYLINDER

COMPARE
.-----;~

SN3 BUF 00 H5N3 BUF \2I9H
SN2 SHIFT 15 IN H

iO liNES

(SS5)

REG!STER
(SN3)

10 LINES

'5 LINES
SECTCJl PULSE
SECTOR COUNTER
INDEX PULSE

(DPG)

5 LINES

SECTOR

DP6 SECT CNT 00 HDP 6 SECT CNT 04 H

COMPARE

L.OG!C
SS3 SECT DES 00 H SS 3 SECT DES 04 H
5 LINES

RG5 DES SECT TK SEL L - - - - - ,
RG5 WRT REG L

(SS2)

10 LINES

SS2CYLDIF

-l ~~~~~ I

5S5 SECT
COMP H

I
I

f----.

4
COMPARE

TRACK REGISTER

LOGIC

SN5 EBl (1) L

DPG LAST SECTOR H

1. THE DESIRED SECTOR ADDRESS IS CONVEYED OVER
LINES DP\2I C00 AS - DP'" C04 AS. THE DESI RED
TRACK ADDRESS IS SENT OVER LINES DP£) TC 08 AS
THROUGH DP0 TC 12 AS

2. DCA and associated logic are implemented for either
an RP05 or an RPOG depending on the drive type.

t----.LAST CYL H

SS5 SECT
TRK COMP H

SS 3 TRACK 130 H-

/-~~--S-S-3-TR-A-C-K-0-4-H---_.----~
5 LINES

DP{1l TC 12 AB

____ SECTOR/TRACK

(S53)

~ RG1 CYL OFF/DIF¢9 H

SS 2 DCA = CCA H

DESIRED SECTOR I

( SECT DES I TRACK)

RG1

09H

MAX TRK. AND / - - - . 5 S 4 AOE SET (1) L
CYL. DETECT
ILLEGAL
ADDRI t-----.SS4 IAE 5ET (1) L
(SS5)
AOE DETECT
IL -_ _ _ _ _ _ _ _ _+-~------------------~~ LAST BLOCK / - - - · L B T
TRANSFER
/ - - - . SS4 TRACK 18 H
DETECT

DPI1 CI1>I1> AB

RG3

10 LINES

MULTIPLEXER

ADDRESS
REGISTER

(SS4)

(SEE NOTE 1)

DIFFERENCE

ss0 CCA CLK H

DP6 SECT CNT 11>0 HDPG SECT CNT ¢4 H

10 LINES

RG1 CYL OFF/DIF 0taH

LOGIC

SN:3 BUF 1010 H - SN:3 BU F ~4 H i
SN3 BUF 08 H - SN3 BUF 12 H

SUBTRACT

(SS1 )
DATA
BUFFER

r--r--

CYLINDER
OFFSET I

(5S5)

SS3 TRACK ¢0 H
553 TRACK 04 H
5 LINES

GOO H
L-._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

04H - } TO MA0
SS3 TRACK 00H

CP-2085

Figure 2-7 Disk Addressing Logic Block Diagram

2-47

2.4.5.1 Cylinder Addressing - Cylinder addressing begins with loading the desired cylinder address (DCA) register
prior to executing the instruction (seek or read/write) that asserts the SEEK/OFFSET GO PULSE to the Drive. The
cylinder address register is a 10-bit register capable of addressing any of the addressable cylinders comprised in the
disk.
The cylinder address is supplied to the desired cylinder address register from the dual controller (DP) logic via the
lines designated DPO COO AB through DPO C07 AB and also DPO TC08 AB and DPO TC09 AB.
Signal RGS DES CYL ADR SEL L together with RGS WRT REG L effect parallel loading of the address into the
DCA register provided that RG3 GOO H is not asserted.
Once loaded, the desired cylinder address (DCA) is applied to the cylinder address subtract logic whose outputs
determine the magnitude and direction of the head movement. The cylinder address subtract logic develops its
outputs by subtracting the current cylinder address (CCA supplied from SSI) from the desired cylinder address
(DCA) resulting in three possible computational actions:
1.

If (DCA) - (CCA) is greater than zero, no borrow is generated by the cylinder address subtra~t logic and
the direction of the head movement is forward. (In this case, signal SS2 CYL DIR H is not asserted.) The
magnitude of head movement is determined by the contents of the 10 output lines, SS2 CYL DIF 00 H
through SS2 CYL DIF 09 H.

If (DCA) - (CCA) is less than a zero, a borrow is generated by subtraction logic and the direction of
drive head movement is reverse. (In this case, signal SS2 CYL DIR H is asserted.) Again, the magnitude
of head movement is defined by the content of the ten difference lines.

If (DCA) - (CCA) is equal to zero, the output of the cylinder address subtract logic is equal to zero and
no movement of the heads is initiated.

Signals SS2 CYL DIF 00 H through SS2 CYL DIF 09 H are multiplexed with the outputs of the offset register in the
register logic (RGl) before being sent to the drive via the MDLI interface. These signals are also sent to the DCA =
CCA detect logic, which determines if the DCA and CCA are equal. If all ten difference lines are zero, it indicates
that a seek operation need not be initiated or that a seek operation has just been completed. An all zeros condition
asserts signal SS2 DCA =CCA H to enable clocking the sector found flip-flop (in the SSO logic) now that it has been
determined that the heads are properly positioned.

•

Substituting the Desired Cylinder Address for the Current Cylinder Address - When the outputs of the
cylinder address subtract logic are received by the Drive, the Drive drops the FILE REAQY line and
kceps it low until the head positioning process is complete. Reassertion of the FILE READY signal
informs the DCL logic that the read/write heads are now positioned over the desired cylinder. The
contents of the current cylinder address register must now be updated by inserting the contents of the
desired cylinder address register into the current cylinder address register. The DCL logic does this by
generating SSO CCA CLK H as a high at the reassertion of the FILE READY signal. Once the
substitution is completed, the desired cylinder address becomes the current cylinder address because this
is where the read/write heads are now positioned. When the substitution occurs, signal SS2 DCA = CCA
H is asserted.

•

Cylinder Address Updating (Mid Transfer Seek) - During extended read/write operation, (e.g., when
data block overlays two or more cylinders) the desired cylinder address register is incremented when
transfer is complete, or when the last track of the cylinder address has been read from/Written on.
Clocking to update the cylinder address is provided by signal SS3 CLR TRK H.

2-48

Updating the cylinder address means that a difflerence exists again between the contents of the desired
cylinder address register a.nd the current cylinder address register. As a result, the following occurs:
1.

The cylinder address subtract logic issues new outputs that are fed into the Drive over the SEEK
DIRECTION LEVEL and CYLINDER DIFFERENCE OFFSET lines.

A seek/offset GO signal is sent to the Drive.

The Drive lowers the FILE READY lint! until the process of moving the heads to the newly
addressed (next) cylinder is completed.

The drive reasserts the FILE READY line causing substitution of the desired cylinder address for
the current cylinder address, etc., as described in the preceding paragraphs.

In this way, a new seek ils carried out each time: the contents of the desired cylinder address register are
updated.
•

Cylinder Overflow DeteGtion and Invalid Cylinder Address - The DCL logic contains circuits for
detecting when the cylinder address exceeds the :addressable cylinders contained in the disk. If, during an
extended read/write operation, the desired cylinder address register is updated to a count exceeding 410
(for an RP05) or 814 (for an RP06), then the address overflow error flip-flop is set to produce signal SS4
AOE SET (1) L.

If the operating system loads the desired cylinder address register with an invalid address, i.e., exceeding
410 (for an RP05) or 814 (for an RP06), then the invalid address error flip-flop is set to generate signal
SS4 IAE SET (1) L.
•

Cylinder Compare Logic - The contents of the desired cyHnder address register are also applied to the
cylinder compare logic .and compared with the cyHnder address read from the disk during header
verification. When the cylinder address (word 1 of sector header field) read from the disk matches that
contained in the desired cylinder address register, the cylinder compare logic asserts signal SS5 CYL
COMP H to indicate a valid matchup. Signal SS5 CYL COMP H is used by the header handling logic as
one factor in the header identification/verification process.

2.4.5.2 Track Addressing - Since all Drive read/write heads are positioned during the cylinder addressing process,
no mechanical movement is necessary for track addressing. Hence track selection is effected by simply supplying the
address over the five head select lines going to the drive.
The track address supplied from the controller is loaded into the desired sector/track register prior to executing the
read/write command. Signal RG5 DES SECT TK SEL L (register select) ANDed with signal RG5 WRT REG L (write
register) clocks the track address into the desired sector/track register. Signals SS3 TRACK 00 H through SS3
TRACK 04 H at the output of the registers convey the track address to the Drive via the interface logic. Then the
Drive selects the addressed head for the read/write operation..
•

Updating the Track Address -- When all sectors on a particular track (20 or 22 depending on format)
have been read/written during an extended read/write (e.g., transfers conveying 2 or more tracks), the
track address must be updated to select the next read/write head for continuing the operation. With a
read/write operation in progress, the GO bit is set and signal RG3 GOO H is asserted. This allows
incrementing the track address when the transfer is complete or on transfer of the last sector of the
track.

2-49

During extended read/write operations the track address can be incremented from 0 to a maximum
count of 18 (19 tracks). When a count equal to track 18 is detected in the desired sector/track register,
signal SS4 TRACK 18 H is asserted. At the completion of the track 18 transfer, this signal is eventually
used to clear the track bits and thereby addre'ss the first track (track no. 0) of the next cylinder.
•

Sector/Track Compare Logic - When reading sector headers from the disk for header identification
purposes, the contents of the second head(~r word are compared against the track bits of the desired
sector/track register (the sector bits are also compared against the output of the sector counter). This
comparison occurs in the sector/track compare logic which looks at the data buffer register (contains
second header word from disk) and the desired sector/track register to determine the match up. (This
compare logic also receives sector count information from the sector counter.) When a match occurs,
signal SS5 SECT TRK CaMP H is asserted to inform the header handling logic that a valid comparison
has been made.

2.4.5.3 Sector Addressing - Sector addressing occurs when the sector address is written into the sector field of the
desired sector/track register. This is performed before the controller executes the read/write comman:d. The sector
field from the desired sector/track register is compared with the sector count from the sector counter. When a match
occurs between the addressed sector and the count from the sector counter, signal SS5 SECT CaMP H is asserted.
This is important to the search logic because it initiates header comparison.
The sector field of the desired sector/track register is also updated at the completion of each sector transfer when a
read/write operation is in progress. Incrementing the count is accomplished by signal SN5 EBL (1) L, which is
asserted at the end of each sector after transfer is complete. Signal DP6 LAST SECTOR H (asserted to indicate last
sector of a track) is used to clear the sector/track register following the transfer of last sector on a track.
2.4.6 Error Correction Code Logic Block Diagram Discussion
Figure 2-8 is a block diagram of the circuits used to implement error correction processing within the DCL. The
circuits on this diagram can be looked at as performing three separate functions, all related to error correction code
processing.

Generation of a 32-bit ECC redundancy code during write operations. This information is written
serially on the disk immediately following thl~ 256 word data field (Figure 2-6).

Checkout of the ECC redundancy field during read operations to detect the possible presence of a data
check error. The check is made by ORing together the low order 21 bits of the ECC register and looking
for a zero status.

Entry into the error correction process on detection of a data check error indicated by the fact that the
low order 21 bits of the ECC register are not zeros. This has two immediate effects with respect to the
Massbus Control Interface lines:
•

The end-of-block (EBL) signal normal1y inserted at the end of a sector is inhibited or delayed until
completing error correction processing.

•

The data(;heck error (DCK) bit in Error Register 1 is set causing the setting of the composite error
bit in the status register and subsequently raising of the ATTENTION line.

Following the error correction process, the DCL detects one of two conditions:
1.

Detects the II-bit error burst and its position (physical location within the data field). The, burst pattern
and position information are supplied to the software operating system via the appropriate registers.

Determines that the error is non-correctable and sets the error correction hard (ECH) error bit in Error
Register 1.
2-50

EC0

SH FT CLOCK H

SHIFT
CLOCK
ENABLE
GATE
(EC2)

N CODE
WORD
COUNTER
(EC2)

I
I

r--L--

I
SNI READ COM OR H

PATTERN
REGISTER

DATA FIELD
ENTRY/HARD
ERROR DETECT
(COMPARATOR
CIRCUIT. EC2 )

~~~~:rX
t-- -

POS. REG
SHIFT
CLOCK
ENABLE
GATING
(EC2)

ECC
POSITION
REGISTER
(EC2)

r----

SN7 DATA

DATA
CHECK
ERROR
DETECT

ECC
CORRECT!ON
ENABLE
(EC3)

I
I

TO
MASSBUS
INTERFACE

EC2 ECC POS REG 00 H

EC2 ECH (1) L

PART OF ERROR REG #1

1
1

EC2 ECC POS REG 11 H
I

EC3 EC CORRECT EN
RGI ECI L

SNI WRITE COM OR H

EC2 NCODE
WRD HICNT(1) H

I 1

ERROR
8URST
DETECT
(EC3)

-lRG0 ERR REG 01 (06)(f) H

BIT 6

EC3 ECC READY L

GEN~~}TlON SN5 E BL (1) L
LOGIC
(SN5)

ECI ZERO
DETECT L

EC3

DCK H
TO
MASSBUS
INTERFACE

SN6 ECC/
CRC DATA H

PART OF ERROR REG. # 1

ECI ECC PAT REG 31 H

L
SN7 ECC
ENVELOPE

(fl H

EC0 SHFT CLK H

ECC CODE
WRITE
CONTROL
FLIP-FLOP
(EC3)

L
r--

EC3 ECC REG
FDBKCTRL H

ECC READY L

r-----

r--

SHIFT
CLotK
ENABLE
EC0 SHFT ClK H

---

ECC
REGISTER
ECC
REG
FEEDBACK
GATING
(ECIl

I
I PA~~~
I REGISTER
1 (BITS
I 21-31)
I

ECC
REGISTER
(BITS
0-20)
(EC 1)

~
I
I

BIT 15
(RGO)

i
EC3

r--I~G~
rt 10 r.rtrt rtr." 101 lIol\il H

EC3 SET DCi< L

ECI ECC PAT REG 31 H
I

I ECI ECC PAT REG

21 H

TO
MASSBUS
} INTERFACE

ZERO
DETECT
GATING
(EC1)

I
EC3 SHIFT IN L TO SN2

Figure 2-8 Error Correction Logic Block Diagram

11-2583

2.4.6.1 Generating and Writing the ECC Field (Write Operation) - Generating and writing the ECCredundancy
code in the ECC field (Figure 2-6) occurs when the DCL executes either of the write commands. The code is formed
within the ECC register during the time that the data field is written onto the disk. Each bit shifted from the shift
register (for transfer to the disk) is also entered into the ECC register. This is accomplished as fol1ows:
a.

Signal SN1 WRITE COM OR H (applied to the ECC register feedback control logic) is asserted since a
write operation is in progress.

At the start of the data field, signal SN7 DATA ENVELOPE (1) H asserts. This in turn causes signal EC3
ECC REG FDBKCTRL H to switch high and enable the ECC register feedback gating.

ONEs and ZEROs coming from the shift register (signaJ SN6 ECC/CRC DATA H) now enter the ECC register
throughout the data field transfer. In this way, the ECC redundancy code (to be written onto the disk following the
data field) is formed. At the end of the data field, signal SN7 ECC ENVELOPE (1) H asserts because itis now time
to write the ECC field associated with the data just written. The latter signal is applied to the ECe code write
control flip-flop as an enabling level. Also applied to the flip-flop is the output of the ECC register (EC 1 ECC PAT
RI~G 31 H). The ECC code write control flip-flop is now set/reset (consistent with the bits coming out of the ECC
register) to form serial pulse train EC3 SHIFT IN L. This pulse train is written onto the disk as the ECC field.
2.4.6.2 Checkout of the ECC Redundancy Code (Read Operation) - During read operations, the ECC redundancy
code is formed again by applying each data field bit read. from the disk to the ECC register. When reading from the
disk, the enabling of the ECC register feedback gating is effected in the following way:
a.

With a read operation undertaken, signal SN1 READ COM OR H (applied to the ECC register feedback
control logic ) is asserted.

At the end of the header gap, signal SN7 DATA ENVELOPE (1) H asserts to define the start of the data
field.

Signal EC3 ECC REG FDBKCTRL H now asse-rts to enable the ECC register feedback gating and thereby
allows each bit coming from the disk (SN6 EOC/CRC DATA H) to enter the ECC register.

Applying each bit read from the disk to the ECC register (with the feedback loop enabled) reconstructs the same
code that was attached to the ECC field when the data wa:; written.
When the end of the data field is reached, signal SN7 DATA ENVELOPE (1) H negates; however, signal SN7 ECC
ENVELOPE (1) H immediately switches high to maintain signal EC3 ECC REG FDBKCTRL H at the asserted level
allowing the ECC field bits coming from the disk (SN6 ECC/CRC DATA H) to enter the ECC register while the
feedback loops are still enabled.
When the ECC redundancy code read from the disk and clocked into the ECC register matches that developed (in
the ECC register) at the close of reading the ECC field, then the 21 low order bits of the ECC register all contain
zeros. This means that the data field has checked out OK. As a result, signal EC1 ZERO DETECT L asserts and
sector processing is terminated normally by raising the EBL signal to the controller.
NOTE
The 21 low order bits of the ECC pattern register are inverted
and then wire ORed together. When all bits are zeros, signal
ECI ZERO DETECT L asserts.
When the 21 low order bits of the ECC register fail to contain all zeros, it means that there is an error in the data
read from the disk. The actual location and the nature (soft or hard) of that error is not known at this time. The
DeL now enters the error correction process (provided it is not inhibited from doing so) as described in the
subsequent paragraphs.

2-52

2.4.6.3 Error Correction Processing - When signal ECI ZERO DETECT L fails to assert at the end of the ECC
envelope, the data check error detect logic issues three outputs that are used as follows:
1.

Signal EC3 SET DCK L asserts to set bit 15 (data check error, DCK) in Error Register 1.

Signal EC3 DCK H asserts. This is used in the synchronous logic to inhibit generation of the end-of-block
(EBL) signal.
NOTE
If the Error Correction Inhibit (ECI) bit in the offset
register iis set, an EBL signal is sent to the controller even
though signal EC3 DCK H asserts. The error correction
proc1ess lin this case, is inhibited.

EC3 DCK H is applied to clock the ECC correction enable logic. The latter circuit now asserts EC3 EC
CORRECT EN provided that the error correction inhibit signal (RG 1 ECI L) is negated.

Assertion of EC3 EC CORRECT EN begins the error correction process and has two immediate effects:
1.

It asserts signal EC3 ECe REG FDBKCTRL H via the ECC register feedback control logic to enable the
ECC register feedback paths. (This is essential for the error correction process.)

Enables clocking of the N Code word counter to maintain a count of each bit serially shifted within the
ECC register.
NOTE
The polynomial used for th.e error correction process is
capable of accommodating :a data field much larger than
the 256 word data field of each sector. For this reason,
the DCL goes through a process of shifting leading zeros
with.in the ECC register and feedback paths. The
N Code word counter maintains a count of the leading
zeros. This is done so the time at which error correction
code processing enters the data field can be decoded and
the task of detecting the II-bit error burst can begin.

The number of leading zeros shifted within the pattern register depends on whether the 18-bit or 16-bit format is
being used. The leading zero values are as shown below:
LEADING ZEROS
18-bit

38,347

DATA FIELD

ECC FIELD

~~------------~~--..--------~--,

-1 1 1 - - - - -

I1~ADING ZEROS

16-bit

38,859

'----,

DATA FIELD
ECC FIELD
, ~~----------·--~I---------~I~I
~

~~----

When the applicable number of leading zeros has been counted, the data field entry detect logic asserts signal EC2 N
CODE WRD HICNT (1) H. This acts as an enabling signal to the position register shift clock enable gating. The
position register keeps a count of data field bits shifted (in the ECC register) until such time as the II-bit error burst
is located. A second use of signal EC2 N CODE WRD HICNT (1) H is its application to the error burst detect
circuits. Here it acts as an enabling signal, (Le., in an anticipation of detecting the II-bit error burst) because the
shifting of bits is now within the data fielld.
2-53

Conditions are now set up for detecting the presence of lthe error burst in the 11 high order bits of the ECC register.
That portion of the ECC register is also called the "ECC pattern" register. Design is such that the locatIon of the 11
bit error burst is detected as being identified when the 21 low order bits all contain zeros (Le., as a ~resu]t of the
continuous shifting/feedback process). An all zero condition is sampled in the zero detect gating and 'asserts signal
ECI ZERO DETECT L. On application to the ECC correction enable logic, signal ECI ZERO DETECT L
immediately negates EC3 ECC CORRECT EN to produce the following results:
a.

Inhibits the position register shift clock enable gating to stop the count of the position register at that
point in the data field (or ECC field). The count stored in the "ECC position" register identifies the
physical location, within the data field, of the fust bit of the II-bit error burst.

Causes the error "burst detect logic to assert signal EC3 ECC READY L. This, in turn, has a double
effect:

Inhibits the ECC register shift clock enable gating so that no further shifting of bits occurs in the
ECC register. This is necessary because the 11 high order bits ("ECC pattern" containing the error
burst) must now be sent to the central processor.

Forces the EBL generation logic to send an end-of-block signal to the controller. This is done to
indicate that error correction processing is complete and that the CPU may now takethe contents
of the ECC position and pattern registers.

Inhibits further counting by the N Code word counter.

This completes DCL error correction processing for those cases where the location of the error burst is detected
within the data field and the error is correctable. If the error correction logic fails to detect an error burst within the
data (or ECC) field, the DCL notifies the CPU of a "hard error" condition. This condition is indicated to the logic
by the fact that the N Code word counter has exceeded the maximum size of the entire ECC code length without
having found an all zeros condition in the low order 21 flip-flops of the ECC register.
NOTE
By definition, "hard error" means that the DCL failed to
detect a correctable error burs;t within the data or ECC fields.
The error correction logic keeps a count of the bits being shifted in the pattern register after the shifting process
enters the data field. Consequently, when the N Code word counter reaches a value of 4128 1 0 bits* (following entry
into the data field) it means that no error burst has been detected and the ECH bit in Error Register 1 must be set.
This occurs when the data field entry/hard error detect logic determines that the count from the N Code word
counter has gone past the ECC field and asserts signal EC2 ECH (1) L.

*16-bit mode. The value of 4128 10 represents 256 words times 16 bits plus 32 bits of ECC field. In the IS-bit mode, the value for
detecting a hard error is 4640 1 0 (256 words times 18 bits plus 32 bits of ECC field).
.

2·54

CHAPTER 3
S:E~RVICE INFORMATION

3.1 GENERAL
Because no adjustment procedu]['es ar(: necessary when servicing the DCL, this chapter consists entirely of detailed
theory covering flow diagrams, timing diagrams, and logic diagrams within the print set. Discussions here center
primarily on the flow diagrams that il1ustrate the step-by-step sequences used to implement DCL control operations.
Certain circuit groups such as those implementing the header compare process and those involved in byte counting
are also described here in greater depth.
3.2 DeL POWER SUPPLY AND POWER MONITOR
The power source for the DCL is a digital standard H764 supply located behind the hex printed circuit board nest.
This power supply develops three different dc output voltages that are distributed within the DCL in the following
ways:
1.

+5 Vdc supplies the integrated circuit chips on all hex PCBs in the DCL. This supply also feeds logic
circuits on the MDLI PCBs.

-15 Vdc is used in the MDLI MAO PCB.

+15 V is fed to the power monitor.

The H764 power supply is turned on by throwing circuit breaker CBI at the base of the drive. When this circuit
breaker is activated and power is applied to the DCL, certain control flip-flops are cleared as part of the power up
process. These flip-flops are:
1.

Composite error

Port A/Port B request flip··flops

Port A/Port B lock flip-flops

Offset mode flip-floJP.

The pins, over which power is applied to each PCB, are indicated on the first page of PCB subsets making up the
complete drawing set.
The power monitor unit provides a constant check of DCL voltage conditions. As long as line and dc power voltages
remain within tolerance, the POWER OK signal is asserted. When the line and dc voltages fail, the AC POWER and
DC POWER signals (in sequence) are raised to set error flags. The negating of the CONTROL GROUND signal
occurring on a power loss informs the Drive that the DCL has lost power.

3-1

3.3 ASYNCHRONOUS DATA TRANSFER (HANDSHAKE)
3.3.1 Writing a Register
The asynchronous data transfer - write register - sequence loads one of the interface registers with data from the
control bus to prepare for a command sequence (see drawing number RP04-O-28). The interface registers that can be
loaded during a write register sequence are:
1.

Desired Cylinder Register

Desired Sector/Track Register

Offset Register

Error Register 01

Error Register 02

Error Register 03

Maintenance Register

Attention Register

Control Register

Prior to the start of the write register sequence, the Drive unit is addressed, the register to be written is selected, and
a write register sequence is specified. The Drive unit is addressed by comparing TCO DRV SEL A with DP2
DISPLA Y (1,2,4). If they match, DP2 MACH SELED A asserts, indicating that this Drive has been selected. DP2
DISPLA Y (l ,2,4) is the Drive unit number, in binary, as determined by the position of the three topmost Drive
address switches on the DP printed circuit board. TBO REG SEL A (00:02) and TAO REG SEL A (03:04) decode to
select the register to be written; the assertion of TAO CTOD A specifies a write register sequence.
The write register sequence is initiated by the assertion of MASSDEM on the MASS BUS which causes DP3 REC
CONT EN A to assert enabling the control bus receivers to gate the 16 control lines and parity line into the DCL. A
parity check is performed and DP4 ODD PARITY asserts if the check is good.
MASSDEM also asserts DP3 SEL DEM A enabling thE: handshake time generator and end around .counter that
develops time intervals DP3 SYNC EN A, DP3 HS TIM 2 A, DP3 HS TIM 3 A, and DP3 TRANSFER A (drawing
number RP04-O-29).
At time DP3 HS TIM 3 A, the selected register is written. If the attention register is selected, the Drive unit device
code selects one of the first eight control lines of the control bus. If the selected line is true, DP2 CLR ATTENTION
A will assert and reset the attention bit.
Writing the attention register is effected to clear the attention bit. The bit is set by any of seven conditions shown in
the various command flow diagrams. The conditions are 1isted below along with the flow diagram in which they are
shown:
1.

A controller being released while a port request exists. Drawing number RP04-O-32.

Completion of any of the five positioning commands. Drawing number RP04-O-3,4,5 ,6,7.

3-2

Issuing of a seek command, but a seek operation its not performed. Drawing number RP04-O-3.

Completion of a search command. Drawing number RP04-0-8.

A composite error exists but no command sequence is in operation. Drawing number RP04-0-34.

A composite error exists and an interface register is about to be written. Drawing number RP04-0-28.

Whenever the Drive unit goes offline or comes on-line.

If the maintenance register is selectl~d, RG5 ASY WRT gates the data into the register. If any of the remaining
registers are selected, RG5 WRT REG gates the data into the register, but only if a command sequence is not already
in progress.
When the control register is selectt~d, bits (01 :05) of the control bus assert RG3 F (0:4), which is the coded
command to be executed. Bit 00 is the GO bit and asserts RG3 STO GO to enable the GO FF.
After time DP3 HS TIM 3 A, DP3 TRANSFER A asserts and is placed on the MASSBUS signifying that the control
bus data has been written into the interface register. The controller responds with the negation of MASSDEM, which
negates DP3 TRANSFER A to end the write register sequence. If the GO bit in the control register is set, RG3 GO
asserts upon the negation of DPS SEL DEM AB. This initiates the command sequence contained in the control
register.

3.3.2 Reading a Register
The asynchronous data transfer-read-register sequence (drawing number RP04-0-30) reads one of the interface
registers by accessing the register and making its contents available on the control bus. Any of the sixteen interface
registers can be read during a read register sequence.
Prior to the start of the read register sequence, a read sequence is specified, the Drive unit is addressed and the
desired register is selected. The negation of MASSCTOD specifies a read register sequence. The Drive unit is
addressed by comparing TCO DRV SEL A with DP2 DISPLAY (1,2,4). If they match, DP2 MACH SELED A asserts,
indicating that this Drive has been selected. DP2 DISPLAY (ll ,2,4) is the Drive unit number, in binary, as determined
by the position of the Drive address switches.
TBO REG SEL A (00:02) and TAO REG SEL A (03:04) asserts DPS REG SEL AB (00:04), which decodes to select
the register to be read. The desired register is selected by enabling a multiplexer which gates the register contents to
the RG2 CONT OR (00: 15) lines.
If the attention register is selected, an RG2 CONT OR (00:07) rendezvous is enabled. The DP2 DISPLAY (1,2,4)
drive address selects one of the first eight control OR lines, if the attention bit DP2 AT A A is set, the selected line
will be true.
A similar rendezvous asserts one of ei.ght DP2 ATA A BIT (00:07) lines. However, the eight AT A A BIT lines are not
gated to the MASSBUS while DPS PORT A ON is true. If controller B had acquired the Drive, DPS PORT A ON
would be negated and the attention A bit would be gated to the control bus [MASS C (00:07)] . Thus the controller,
not having control of the Drive (in this case controller B), can still read its attention register.
Controller B can access the B attention bit by asserting DP2 AT A REG SEL B even though the Drive is acquired by
controller A. DP3 TRAS B EN asserts to gate out the attention bit when controller Braises MASSDEM on the B
Massbus.

3-3

The read register sequence is initiated by asserting MASSlDEM, which causes DP3 TRAS A EN and DP3 PARITY EN
A to assert. These latter signals enable the control bus transmitters to gate the DCL to the 16 control lines and the
parity line on the MASSBUS.
MASSDEM also asserts DP3 SEL DEM A, enabling the handshake timing generator that develops time intervals DP3
SYNC EN A, DP3 HS TIM 2 A, DP3 HS TIM 3 A, and DF'3 TRANSFER A (draWing number RP04-O-29).
At time DP3 HS TIM 3 A, the selected register (except the attention register) is read out to the control bus. RG5
ASY READ docks the control OR Hnes into the control output register asserting DPO TC (00:07) A and DPO TC
(08: 15) AB to the MASS BUS . The first eight bits of the control word route to the MASS BUS via a port A/port B
multiplexer. While DPO TC (00:07) A is routed to MASS.C (00:07) of MASSBUS A, the multiplexer is routing the B
attention bit to MASSC (00:07) of MASSBUS B.
After time DP3 HS TIM 3 A, DP3 TRANSFER A asserts and is placed on the MASSBUS signifying that the contents
of the selected register are now on the control bus. The ,;::ontroller responds with the negation of MASSDEM, which
negates DP3 TRANSFER A to end the read register sequence.
3.3.3 Dual Control
3.3.3.1 Port Acquisition (drawing number RP04-0-31, 33A) - If the Drive unit isin the neutral state,controller A
can acquire control of the Drive by addressing it and asserting MASSDEM. If the controller requests a read register,
MASSDEM holds the Drive for the HANDSHAKE read register sequence. When MASSDEM negates, the Drive
returns to the neutral state. If the register selected is the control register, or the controller requested a write register
sequence, a port A request latch is set during the handshake. When MASSDEM negates, the port request latch
continues to hold the Drive until a port release command is issued or a one second time-out elapses, whichever
comes first.
If controller B has control of the Drive when controller A makes its request, the port A request latch is still set.
When controller B releases the Drive, the port A latch causes controller A to automatical1y acquire control of the
Drive.
The Drive unit is addressed by comparing TCO DRY SEL A (00:02) with DP2 DISPLAY (1 ,2,4). If they match, DP2
MACH SELED A asserts, signifying that this Drive has been selected. DP2 DISPLAY (1,2,4) is the binary
representation of the Drive unit number as determined by the position of the three topmost drive address switches
on the DP printed circuit board.
Port Acquisition is initiated by the assertion of MASSDEM. DP3 SEL DEM A asserts and enables the handshake
timing generator - and end-around counter that develops time intervals DP3 SYNC EN A, DP3 HS TIM 2 A, and
DP3 HS TIM 3 A (drawing number RP04-O-29). At time ))P3 SYNC EN A, if DP5 PORT B ON is negated, controller
A acquires the Drive in sync with handshake dock A and asserts DP5 PORT A ON.
DP3 SYNC EN A also asserts DP3 INHIBIT A SET, which inhibits controller acquisition during the latter part of the
handshake cycle. The asynchronous transmitters and receivers are not enabled until DP5 PORT A ON is true. They
must be enabled early in the handshake cyde to gate the control bus to the DCL and al10w time for the interface
register to be accessed.
At time DP3 HS TIM 2 A, a port request is made if controller A requests a write register sequence or requests to read
the control register when controller B does not have control of the Drive (neutral state). Once DP5 PORT A REQ is
asserted, the request state is held until controller B releases control and DP5 PORT B ON is negated. When this
occurs, controller A acquires the Drive and DP5 PORT A ON asserts. A port request is made at time DP3 HS TIM 3
A if the attention bit has cleared (DP2 CLR ATTENTION A asserted).

3-4

3.3.3.2 Port Release (drawing number RP04-0-32, 33B) - In the referenced port release flow diagram, a condition
is assumed of controller A having control of the Drive unit with DPS PORT A ON asserted.
One means of releasing port control is via a release command sequence. When the GO FF is set, RG3 RELEASE
COM asserts and sets the DPS RELEASE A FF. This resets: the DPS PORT A REQ FF and two handshake clock
cycles later, DPS PORT A ON is negated . If a port B request ,exists, controner B acquires the Drive and DPS PORT B
ON asserts in sync with handshake clock B (SO ns later).
A port release also occurs if DPS SEL DEM AB is asserted longer than one second under conditions where no
command sequence is in progre!ss. In this case, the DPS RELEASE A FF sets and the release sequence just described
occurs.
3.3.3.3 Simultaneous Controller A and Controller B Demands (drawing number RP04-0-33, C) - The referenced
diagram illustrates the condition wh~~re MASSDEM is assertl~d simultaneously by controllers A and B. NotIng that
handshake clocks A and Bare 180-d,egre:es out-of-phase, the diagram shows that the controller whose clock has the
next rising edge (following the assertion of DEMAND) seizes the control. The acquisition sequence is as shown in
drawing number RP04.Q-31. Drawing number RP04.Q-33, C shows those time periods when simultaneous demands
would seize controller A and the alternate periods when control1er B would be seized.
3.4 MECHANICAL MOVEMENT
3.4.1 Seek
The seek sequence positions the! Drive unit heads over the cylinder whose address is contained in the desired cylinder
address register. When a seek command is to be executed, the contents of the desired cyHnder address (DCA) register
and the current cylinder address (CCA) register are compared. If a difference exists, a seek is performed to reduce
the difference to zero. If a sector search or any synchronous data transfer command is issued, the desired cylinder
address and current cylinder address registers are examined. If DCA =1= CCA, an impJied seek is performed before the
command is executed.
3.4.1.1 Seek Flow (drawing number RP04-0-3, 12) - The GO FF is set, asserting RG3 GO and starting the seek
command sequence. RG3 SEEK COM is decoded from the function code in the control register. If DCA =CCA, a
seek is not required; the command is l:erminated by resetting the GO FF and setting the attention bit.
A bad address (SS4 BAD ADDR) also inhibits the SEEK s~~quence and causes a command termination. SS4 BAD
ADDR asserts if the desired cylinder address is greater than the number of addressable cylinders (411 for the RPOS;
815 for the RP06), the track address is greater than 18, or the desired sector is greater than 19 (I8-bit mode, 21 in
the 16-bit mode).
The Drive does not execute a SEEK while in the offset mode. If the Drive is in the offset mode and a seek command
is issued, SSO SS RTC is asserted and the flow branches into a return to centerline process. This causes return of the
heads to track centerline and takes the Drive unit out of the offset mode. Exit from the return-to-centerline process
occurs on the negation of RGS OFFSET MD.
RGS MOV COM is asserted by SSO SEEK GO and enables ,m end-around counter. The counter is clocked by DP6
FUNC SECT ClK and develops move timing gate RGS MOV TIM 1, RGS MOV TIM 2, and RGS MOV TIM 3. After
the three timing gates have been developed, the counter resets to its initial state until another RGS MOV COM is
issued (Figure 3-1).
RGS MOV TIM 2 asserts RGS SEEK/OFFSET GO which triggers the seek operation within the Drive unit. When the
Drive has completed the seek operation and the heads are positioned over the desired cylinder MBO FILE READY is
asserted. MBO FILE READY terminates the command by resetting the GO FF and setting the attention bit. SSO
CCA CLK is asserted and transfers DCA into the current cylinder register making DCA =CCA.

3-5

---i

1 BYTE

------.j I. 24 JJ. s
I
I

DP6
FUNC SECT CLK

RG5
MOV COM

13,440 CLK PULSES PER. REV.

I
I

nYnL

.-J

:I
I

:
I

I
I

L~_ _

D3~

R3(1)

I--

I
14--

~8!~S---1~

-+.__ I
:

R0 (1) _____ II
I

---I.

____~_______________________

R0(0) ---II----'l~~S
,_T_I_M_1__..,..-_ _~
I

R1 (1)

----+I------J
I

R1 (0) ----+-I-------~
I
2 BYTES- 2.48
JJ.s
RG .;;.,5..;.,;M.;.,;;0;.";.V.-,,;.,T;,;,;IM.;.,,.,;;;.2_...A

r-I
I
I

R2(1)---~I----------·-----...A
I

R2(0)---~I--__---.----~
: - 3 BYTES - 3.72 JJ.s

===t

RG 5 MOV TIM 3
11-2464

Figure 3-1 Move Timing Diagram

3.4.1.2 Implied Seek (Figure 3-2) - The seek flow (RP04-O-3) can be entered from a sector search flow. When a
sector search sequence (or read/write operation sequence) is initiated and DCA =1= CCA, the sequence is held up until
an implied seek is performed and DCA = CCA. After SSO CCA CLK sets DCA = CCA, the implied seek process is
complete, Command termination (setting attention bit and resetting the GO FF) does not occur because a
positioning command does not exist.
3.4.1.3 Mid-Transfer Seek - During a spiral read or write operation, when the last sector of the last track of a given
cylinder has been read (or written), a seek is needed to move the heads to the next cylinder. SS4 TRACK 18 HOLD,
SS3 EBL, and DP6 LAST SECTOR assert SSI DCA CLK to increment the desired cylinder address register causing a
difference of 1 between DCA and CCA. The next read (or write) sequence asserts SSO SEEK OR (via a sector search
sequence) to initiate an implied seek sequence. After tht: heads have moved to the next cylinder, DCA again equals
CCA and the read (or write) operation can continue.
3.4.2 Offset
The offset sequence displaces the heads slightly off of track centerline by a specified amount and in a specified
direction by the data contained in the offset register. The heads remain offset until a return to centerline command
(issued directly or implied) is issued.

J·6

- - - - : 1 BYTE

DPG

FUNC

r---

: 1.24

SECTCLKiJ~[LJL
I

((

)~j-------------

SS0 SEEK OR

---T------r------+---------------~~r~-------------

SS0 SET SEEK GO

SS0 SEEK GO

SS0 CCA ClK

RG5 MOV COM

I
1

RG5 MOV TIM 1 _ _--+1

I
I
RG5 MOV TIM 2 - - - - t o1
I
1

RG5 MOV TIM 3 _ _~I

I
I

RG5 SEEK /OFFSET
GO PULSE

If---------'l'ri----\--

iI
~I'--

-----'I'rt---___+_

-~~
I

I
I
-----I.

------'I
~RTS WHEN

MB0 FilE READY

IMPLIED
SEEK IS COMPLETE

SN6 COUNT EN _ __
11-2465

Figure 3-2 Implied Seek Timing Diagram

3.4.2.1 Offset Flow (drawing number RP04-0-4, 13) - The: GO FF is set, asserting RG3 GO and starting the offset
command sequence. RG3 OFFSET COM is decoded from the function code in the control register. RG5 OFFSET
MODE and RG5 OFFSET MD assert and remain asserted for as long as the heads are in an offset position.
RG5 MOV COM is asserted by RG3 OFFSET COM and enables the end-around counter. The counter is clocked by
DP6 FUNC SECT CLK and develops move timing frames RG5 MOV TIM 1, RG5 MOV TIM 2, and RG5 MOV TIM
3. After the three timing signalls have been developed, the counter resets to its initial state until another RG5 MOV
COM is issued.
RG5 MOV TIM 2 asserts RG5 SEEK/OFFSET GO which triggers the offset operation within the Drive unit. When
the Drive has completed the offset sequence and the heads are offset from centerline by the desired amount, MBO
OFFSET READY is asserted by the Drive. MBO OFFSET READY terminates the command sequence by resetting
the GO FF and setting the attention bit.

3-7

The sequence shown in drawing number RP04-O-4 offsets the heads by the amount specified in the offset register. If
the heads are to be offset a different amount, or in the other direction, the new OFFSET value is placed into the
offset register (in a handshake operation). Then the OFFSET command is issued and the sequence of drawing
number RP04-O-4 is repeated. The sequence is completed when the heads are over the new offset position.
While moving the heads to the new offset position, the offset mode FF remains set and RGS OFFSET MODE and
RGS OFFSET MD remain asserted. They are negated only when an offset reset pulse is asserted and the Drive
executes a return to centerline sequence.
3.4.3 Return-to-Centerline
Execution of a return to centerline sequence returns the Drive heads from an offset position to track centerline. The
sequence can be initiated by a return-to-centerline command in the control register or an implied return to centerline
derived from a seek command or either of the synchronous write commands.
3.4.3.1 Return to Centerline Flow (drawing number RP04-0-S, 14) - The GO FF is set, asserting RG3 GO and
starting the return-to-centerline command sequence. RG3 RET TO CL COM is decoded from the function code in
the control register.
RGS MOV COM is asserted by RG3 RET TO CL COM and enables an end-around counter. The counter is clocked
by DP6 FUNC SECT CLK and develops move timing signals RGS MOV TIM 1, RGS MOV TIM 2 and RGS MOV
TIM 3. After the three timing signals have been developed, the counter resets to its initial state until another RGS
MOV COM is issued.
During RGS MOV TIM 1, RGS OFFSET RES PULSE is asserted and initiates the return to centerline operation
within the Drive. When the Drive has completed the RETURN-TO-CENTERLINE operation and the heads are
positioned over the track centerline, the MBO OFFSET READY signal is asserted by the Drive. MBO OFFSET
READY terminates the sequence by resetting the GO FF and setting the attention bit.
3.4.3.2 Implied Return to Centerline (Figure 3-3) - The return to centerline flow process can be entered from a
seek flow or from either of the write flows. The respective flow will assert SNI RTC and a return to centerline
sequence will be carried out. When the sequence is completed, RGS OFFSET MD is negated and a return is made to
the SEEK or the WRITE flow.
Note that in Figure 3-3, signal RGS OFFSET MODE is negated at MOV TIM 3 while RGS OFFSET MD is held true
until MBO OFFSET READY is asserted. The negation of RGS OFFSET MODE at MOV TIM 3 causes. the negation
of RGS MOV COM early in the sequence. If the implied RETURN TO CENTERLINE originated from a SEEK flow,
the SEEK command is waiting for the negation of RGS OFFSET MD to assert RGS MOV COM for the SEEK
sequence timing. The early negation of RGS MOV COM ensures that it wi11 have settled in the negated state when
the SEEK command asserts it for the SEEK timing.
3.4.4 Reca1ibrate
The recalibrate command sequence is intended to position the Drive heads over cylinder 000 while clearing the
current cylinder address register.
3.4.4.1 Recalibrate Flow (drawing number RP04-0-6, 15) - The GO FF is set, asserting RG3 GO and starting the
recalibrate command sequence. RG3 RECAL COM asserts from the function code in the control register.
RGS MOV COM is asserted by RG3 RECAL COM and enables an end-around counter. The counter is clocked by
DP6 FUNC SECT CLK and develops move timing signals RGS MOV TIM 1, RGS MOV TIM 2, and RGS MOV TIM
3. After the three timing signals have been developed, the counter resets to its initial state until another RGS MOV
COM is issued.

3-8

-I

10- 1 BYTE

r-I

.-1
I

DP6 FUNC. SECT ClK

SN1 RTC

1.24 p.SEC

JLJL.JLr
I

d=
I

i
I
I

~--!----~-------------~

RG5 MOV COM

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

I
I

RG5 MOV TIM 1

RG5 MOV TIM 2

RG5 MOV TIM 3

RG5 OFFSET RES PULSE
RG5 OFFSET MODE

MB0 OFFSET READY

RG 5 OFFSET MD
11-2466

Figure 3 ..3 Implied Return to Centerline Timing Diagram

RG5 MOY TIM 1 asserts RG5 RECAL PULSE which starts the RECALIBRATION operation within the Drive unit.
The latter signa] also clears the current cyHnder address register (CCA). When the Drive has comp]eted the recalibrate
operation and the heads are centered over cylinder 000, the MBO FILE READY is asserted by the Drive. MBO FILE
READY terminates the command sequence by resetting the GO FF and setting the attention bit.
3.4.5 Unload

An unload command causes the Drive unit to retract the heads, the spindle to cycle down and the STANDBY light
to illuminate. When the START button is pressed the spindle will cycle up to speed and the heads will load
completing the unload sequence.
3.4.5.1 Unload Flow (drawing number RP04-0-7, 16) - The GO FF is set, asserting RG3 GO and starting the
unload command sequence. RG3 UNLOAD COM is decoded from the function code in the control register.
RG3 UNLOAD COM asserts DP4 DEY IN STNBY, which initiates the Drive unit cyc1e down process. Cycling down
the Drive unit causes the heads to retract and the STANDBY Jight to i11uminate. MBI ON LINE now negates
indicating that the disk pack is unavailable.

3-9

Operator intervention is required to finish the command sequence. Pushing the START button initiates the cycle-up
process. After the heads are loaded and the spindle hm; come up to speed, signals MBI ON LINE and MBO FILE
READY are asserted. MBO FILE READY terminates the sequence by resetting the GO FF and setting the attention
bit.
3.5 SECTOR SEARCH
The sector search sequence functions to locate the desired sector loaded into the desired sector/track address
register. A sector timing circuit produces a count of tht! sectors as the disk rotates. The count is compared to the
desired sector, and if they match, a sector found signal is asserted.
3.5.1 Sector Timing (drawing number RP04-0-11, 17)
A multiplexer selects the index pulse and sector clock either from the Drive unit or from the diagnostic circJlitry. At
the beginning of a disk revolution, DP6 FUNC INDEX PULSE will set the sector pulse FF and reset the sector clock
counter and the sector pulse counter.
The sector clock counter starts a count of sector clocks and outputs the count to the sector clock decoder. Th~
decoder looks for a binary count of 608* or 671 * (depending on the format) signifying that the sector is completed.
When this occurs the clock counter is reset and a sector pulse is generated to start the next sector.
The sector pulses are counted and decoded for a sector pulse count of 19 or 21 (depending on the format) as the last
sector signifying that the disk has completed a revolution.
During the last sector, the sector pulse FF is inhibited from setting through normal clocking. On occurrence of the
index pulse, the sector counter is cleared and the sector pulse flip-flop is set to assert sector pu]se No. O.
3.5.2 Sector Search Flow (drawing number RP04-0-8 and Figure 3-4)
The GO FF is set, asserting RG3 GO and starting the SEARCH command sequence. RG3 SEARCH COM asserts
from the function code in the control register. If an mega] address is decoded in either the DCA register or the
sector /track register, the illega] address error {lAE) bit is set and the command is aborted. If the addresses are legal
but DCA =1= CCA, an implied seek is executed. The implied seek process is entered by asserting SSO SEEK OR but
does not progress any further unless DCA =1= CCA. When the implied seek has been executed and DCA =CCA, the
flow exits back to the sector search flow.
At the leading edge of each sector pulse, the sector counter is incremented. If the output of the s¢ctor counter
matches the desired sector address, signal SS5 SECTOR COMP H is asserted. At the trailing edge of the same sector
pulse, the SSO SECTOR FOUND flip-flop is set. Signal SSO SEARCH COMP is then asserted, thereby terminating
the sequence by resetting the GO flip-flop and asserting the attention bit.
~ ... /'" BEGINNING OF NEW SECTOR

DP6 SECTOR PULSE

SS5 SECTOR COMP

~~_'1_.2_4_~_S_E_C________________________

~---- ASSERTS IF SS3 SECT DES < 00: 04> =
:

DP6 SECT CNT < 00 04 >

SS0 SECTOR FOUND

_---'I

11-2467

Figure 34 Sector S,~arch Timing Diagram

*Since a count of zero is given significance, the actual count is one greater than that decoded; i.e., 609 or 672.

3··10

3.5.3 Implied Search
If any of the four synchronous data transfer commands are initiated, an impJied search is executed. RG3 READ
COM, RG3 READ HD DT COM, or RG3 WRITE COM asserts SNI HEADER ENABLE while RG3 WRT HD DAT
COM asserts SNO SECTOR SEARCH. Both header enable and sector search initiate a search sequence. Exit for both
of the implied search flows is SSO SECTOR FOUND.
3.6 WRITE HEADER AND DATA FLOW DIAGRAM DISCUSSION
Drawing RP04-O-26 shows the flow sequence for the write·header-and-data operation (used to format the disk) from
the time command setup occurs until the desired number of sectors have been formatted. A timing diagram, showing
principal control pulses occurring within a sector, is also provided in drawing RP04-O-24.

3.6.1 Command Setup
The write header and data command is initiated when the control register is loaded with a function code of (63 8 ),
This sets the RG3 GO FF allowing the function code decodler to assert RG3 WRT HD & DAT. The setting of the GO
FF also asserts RG3 GOO which is sent over to the Drive as MODULE SELECT to indicate that this particular Drive
has been selected by the controller. The RG3 COM ENA FF is set when the contro11er raises the RUN line (EC 9
RUN). This causes assertion of RG3 WRT HD DAT COM which, in turn, produces the following:
I.

Asserts signal SNI WRITE COM OR H. This is used later (during the sector header gap) to set the write
sector FF.

Generates signal SNO WRT HD EN to set the SNO SECTOR SEARCH FF. With the sector search
flip-flop set, the process of detecting the addressed sector now begins.

3.6.2 Sector Search/Sector Found
If at this time, the contents of DCA ar1e not equal to CCA, an implied seek operation is executed before returning to
the flow process shown on RP04-O-26" If signal SSO DCA:= CCA is already asserted (which results when the implied
seek is completed), detection of the desired sector is initiated. Signa] SSO SECTOR COMP asserts at the leading edge
of the sector pulse if the sector count matches the desired sector address. At the trailing edge of the same sector
pulse, the sector found flip-flop is set.
3.6.3 Pre-Header Field
Setting the sector found flip-flop iniitiates pre-header field processing as fo]]ows:
1.

The sector search flip-nop is cleared triggering a one shot to generate signal SNO GT LD SYNC CLK.
This signal forces the first ECO BUS SYNC CLK which (following receipt of the write clock) results in
loading the first header word into the data buffer register.

The S'NO FORMAT COM FF is set, asserting signal SNO WRITE OR. This enables the write gating logic,
and also asserts signal MAO WRITE COMMAND LEVEL to inform the Drive that a write operation is to
begin.

As a result of the sector pulse, the byte counter is reset to a count of zero, while the data shift register
is cleared. As the byte counter counts up from this time on, a pre-header gap of 39 bytes of zeros is
allowed to pass through the shift register and onto the disk.

3.6.3.1 Writing the Sync Byte - At byte 39 time, signals SNO WRITE SYNC and SNO LOAD SR are asserted to
load the sync byte into the shift register. At this time, the process of serially shifting the sync byte onto the disk is
begun.

3-111

3.6.4 Header Setup Operations and Writing the Header
As the sync byte is being shifted serially onto the disk, various timing operations are being set up to strobe the
header words from the controller into the DCL and then onto the Drive. These are as follows:
1.

SNI SYNC CLK TIME flip-flop is set to enable the ring (word-in) counter and the SNI SYNC CLK EN
nip-flop. In general, this signal envelopes a period when sync clocks are to be generated.

ECS WORD IN (produced by the ring counter) will assert four times during the header area. Each
assertion loads a header word from the data buffer register into the shift register through generation of
SNO LOAD SR. The loading occurs when a complete word has been shifted out of the shift register.

While the serial shifting is in process, the data buffer register is paral1elloaded with the next header word
received from the controller. Signal ECO BUS SYNC CLK is asserted three more times. (The first
assertion occurred earlier in the pre-header area.) Each assertion results in a SN8 WRITE CLK signal and
then a SN4 BUF CLK signal. The latter signaJ para11el loads a word from the controller into the buffer
register.

At byte 5 time (when all header information has been obtained from the controller), the SN8 SYN CLK
STOP flip-flop is set to inhibit further generation of sync clocks.

At byte 8 time after the second key word has been recorded onto the disk, the SN7 ~RC WORD
flip-flop is set to allow the CRC word to be written. Signal SS7 CRC IN represents the eRC word in
serial form. The cyclic redundancy check (CRC) word is the last header information written onto the
disk.
Also at byte 8 time, SNO FORM SYNC TIME CLR asserts to reset the SNI SYNC CL,K TIME FF,
clearing the ring counter and the SNI SYNC eLK EN flip-flop.

At byte 10 time, all header information has been recorded and the SN7 CRC WORD flip-flop is reset. A
header gap of bytes of zeros follows.
.

3.6.5 Header Gap
A header gap of bytes of zeros separates the header field Hnd the data field sync byte. The byte counter is allowed to
continue the header field count up to byte 11. At this point, SNO WRITE COM SET asserts to produce the following:
1.

The byte counter is reset by SNO BYTE CNT SYNC CLR and allowed to count up to byte 9 for a total
of 21 bytes before the data field sync byte is to be written.

The SNO WRITE SECTOR flip-flop is set to maintain the assertion of SNO WRITE ENABLE and MAO
WRITE COMMAND LEVEL. At this point, SNO FORMAT COM flip-flop is cleared.

Signal SNO WRITE COM SET also triggers a one shot to assert signal SNO GT LD SYNCCLK. This in
turn forces a ECO BUS SYNC CLK to the controller. As a result, the first data word is loaded from the
controller into the data buffer register.

3.6.5.1 Data Field Sync Byte - At byte 9 time the data field sync byte is being written. Immediately following the
sync byte is the 2S6-word data block. The synchronous clocking is almost identical to that described in Paragraphs
3.6.3.1 and 3.6.4. Assertion of SNO WRITE SYNC at byte 9 time enables the sync byte to be written onto the disk.
3.6.6 Data Field
After the sync byte is written, a total of 255 more ECG BUS SYNC CLK signals are generated. After the last data
word has been loaded into the buffer register from thl;! controller, the SN7 SYNC CLK STOP flip~flop is set to

3-12

inhibit sync clock generation. After the complete data block has been transferred (at byte count 512), SN8 EOB
BYTE is asserted to reset SNO SYNC CLK TIME flip-flop, disabling the ring counter and SNO SYNC CLK EN
flip-flop. The SN7 DATA ENVELOPE flip-flop is set at the beginning of the data block and is reset at the end of the
data block. This signal enables the generation of the two ECe words that follow the data block.
3.6.7 Error Correction Code (ECC) Field
At the end of the data block, when SN8 EOB BYTE resets SN7 DATA ENVELOPE flip-flop, it also sets the SN7
ECC ENVELOPE flip-flop. As a result, EC3 SHIFT IN, which is the serial representation of the two ECC words, is
asserted. This signal is written onto the disk as the ECC fie!ld before the SN7 ENVELOPE flip-flop is reset by SN8
END ECC BYTE.
3.6.8 Data Gap
A data gap of two bytes of zeros is written following the ECC Field. This occurs before the complete write control
logic is reset by the assertion of SN8 EOB W BYTE. At the assertion of this signal, the SNO WRITE SECTOR
flip-flop is reset disabling SNO WRITE ENABLE and MAO WRITE COMMAND LEVEL; at the same time, SN5 END
COM triggers the SN5 EBL one-shot signaling that the sector transfer is completed. Then EC9 RUN is sampled to
determine if the transfer is to continue" If EC9 RUN is ass,erted, SN5 COM CONT sets the SNO SECTOR SEARCH
flip-flop and re-initiates the complete process. If EC9 RUN is not asserted, signal SN5 RESET GO resets the GO FF
and terminates the command.
3.7 HEADER COMPARE PROCESS (dlrawing number RP04-O-9, 19 and Figure 3-5)
The header compare process is entered from any synchronous data transfer command flow except write header and
data. The purpose of this process is to compare and verify the header read from the disk against the desired cylinder,
desired sector, desired track and the format bit. A CRC check is also performed on the header data. If the desired
cylinder, sector, and track addlress match the header address, and the CRC check is good, SSO HEADER FOUND is
asserted which returns the flow back to the basic command.
The process is initiated by SNI HEADER ENABLE which asserts from RG3 WRITE COM, RG3 READ COM, or
RG3 READ HD DT COM.
Before a header compare can take place, the desired sector must be found. The sector search process locates the
desired sector and asserts SSO SECTOR FOUND at the trailing edge of the sector pulse. The sector pulse resets the
byte counter which starts a byte count of the pre-header field.
When byte 30 of the pre-header field is reached, SNI READ ENABLE enables the DCL read logic circuits. At this
time, SNI SYNC STROBE is asserted to allow the sync byte to be detected by the sync byte decoder. When the
logic recognizes the sync byte, signal SN7 SYNC CLR is asserted to clear the CRC logic before the header words are
shifted in. SN7 SYNC CLR resets the byte counter to begin a byte count of the header. It also enables the ring
(word in) counter to count serial data lbits and assert ECS WORD IN to load a complete 16-bit word from the shift
register into the data buffer. Each time a word is loaded, 3l sync clock is developed. The bus sync clocks are sent to
the controller only during the read header and data command. The first header word loaded into the data buffer by
EC5 WORD IN contains the format bit and the cylinder address. (If the format bit, bit 12, does not match the
format bit contained in the offset register, ssa FMT ERR SET will assert.) If the cylinder address matches the
desired cylinder address contained in the desired cylinder address register, ssa CYL MATCH asserts.
The second header word strobed by EC5 WORD IN is the header sector/track address. If these match the desired
sector and track addresses (in the desired sector/track address register), signal ssa SECT TRK MATCH asserts.
The third and fourth header words are key words and are not verified by hardware. After the key words are read, if
either ssa CYL MATCH or ssa SECT TRK MATCH has not been asserted, ssa HCE (header compare error) is
asserted.

3-13

HEADER

----_14----- HEADER GAP - - - -...

SN1
HEADER ENABLE

.......~_ _ _ _ _ _ _..;.I_

r-l
L-

DP6
SECTOR PULSE

SS0

_____

[RESETS ON BYTE 11 FOR WRITE

1-- DATA COMMAND.

I
I
I
I

RESETS ON BYTE 15 FOR READ
HEADER
DATA AND READ DATA
COMMANDS

I
I

~rl----~fJ~(----~----~fJr(----~--------~------~------------~--~--~LL
I

SECTOR FOUND
SN0

i----------1

.
_____

~~----~~~(----------~Lr(----~--------~------~------------~--~---,LL:,'

SEND HEADER
RESETS AT END OF ECC BYTE
SN1
READ ENABLE

I
I

SN1
SYNC. STROBE

RESETS AT BYTE 0 OF DATA FIELD

I
I

SN7 SYNC. ClR.

SS0
HEADER AREA

SN1
SYNC. ClK. TIME

L
L

SS0 CYL. MATCH

SECT. TRK. MATCH

SS7 CRC. OK.

--.JL
I
I

SS0
HEADER FOUND

RESETS AT BYTE 6 OF DATA FIELD
11-2468

Figure 3-5 Header Compare Timing Diagram

If no HCE is detected, the CRe word (fifth header word) is shifted serially into the CRC logic for the check. At byte
10 of the header field SS7 CRC OK asserts if the CRC checked out properly. Then SSO HEADER FOUND asserts
and an exit is made from the header I~ompare flow. If a CRe error is detected, SSO HCRC set is asserted.
3.8 WRITE DATA FLOW DIAGRAM DISCUSSION
lliustrations of the write header command flow and timing are given in drawings RP04-O-27 and RP04-O-25
respectively.
3.8.1 Command Setup
The write data command is initiated when the control register is loaded with a function code of (618)' This sets the
RG3 GO FF, allowing the function code decoder to assert RG3 WRT DAT. Setting the GO FF also asserts RG3
GOO, which is sent over to the Driv(~ as MODULE SELECT to indicate the particular Drive that has been selected.
RG3 COM ENA FF is asserted when the controller raises the RUN line (EC9 RUN). This results in the assertion of
RG3 WRT COM and SNI WRITE COM EN which clock sets SNO HEADER ENABLE flip-flop to enter the header
search flow.
3.8.2 Pre-Header Field and Header Field
The header search flow begins at the setting of SNO HEADER ENABLE flip-flop and ends at the setting of SSO·
HEADER FOUND flip-flop which indicates a successful header verification. Detail descriptions are given in
Paragraph 3.7 and drawings RP04-O-9, and.I9.
3.8.3 Header Gap
A header gap of zeros follows the header .yerification before the sync byte and data field are written. The byte
counter continues counting from the header field to byte 11. By then, all read control logic and header handling
logic are reset to produce the following:

The SNO WRITE SECTOR flip-flop is set by dearing the SNO HEADER ENABLE flip-flop. From this
point on, all write control logic begins to function.

As the SNO HEADER E;~A1BLE flip-flop is reset, it triggers a one-shot to assert SNO GT LD SYNC CLK.
This signal forces the assertion of ECO BUS SYNC CLK which (on receipt of the write clock) loads the
first data word from the controller into the buffer register.

The byte counter is cleaJred and then renews its count to byte 9. At this point, the write logic is initiated
to write the sync byte and data field.

3.8.4 Data Field Sync Byte and Data Field
From the time SNO WRITE SYNC is asserted at byte 9, all control functions are identical to those described in
Paragraphs 3.6.5.1 and 3.6.6.
In short, SNO SYNC CLK TIME FF is set to enable the ring counter and the sync clock generation. SN7 DATA
ENVELOPE is raised. After a total transfer of 256 words from the controller, the sync clocks are terminated. After
the complete data block is recorded onto disk, the ECC field follows.
3.8.5 ECC Field
Here again, control timing is identical to that described in Paragraph 3.6.7. The SN7 ECC ENVELOPE flip-flop is set
to allow the two ECC words to be recorded.
3.8.6 Data Gap
The termination of the sector transfer (or command) is :identical/to that outlined in Paragraph 3.6.8 with one
exception: if the transfer is to continue, SN5 COM CONT is asserted to set the SNO HEADER ENABLE flip-flop.
The write operation is repeated beginning with the header search process.

3-15

3.9 READ DATA COMMAND/READ HEADER ANID DATA COMMAND FLOW DIAGRAM DISCUSSION
(drawing number RP04-0-10, 18 and Figure 3-6)
These two commands resemble each other functionally to the extent that they both transfer data off the disk and
over to the controller. Their major differences, on the other hand, are:
1.

Header information is transferred to the controller during the read header and data command. During
read data command the header is verified internally within the DCL.

Header errors are flagged, but transfer continues during a read header and data command. During read
data command, header errors abort the command. (See Error Handling subsection.)

Both commands are initiated when the proper command codes (accompanied by the GO bit) are loaded into the
control register. These codes and the related control signals they assert are:
I.

Read data (618) asserts RG3 READ COM.

Read header and data (63 8) assert RG3 RD HD & DAT COM.

Both signals set the SNI HEADER ENABLE flip-flop to initiate the header search process. When this process
concludes, SSO HEADER FOUND asserts to indicate a successful header verification.
NOTE
When the read header and data command is being executed,
the sector search process produces four ECO BUS SYNC clocks
to the controller; that is, one for each header word transferred.
When byte 15 in the header gap is counted, SNI SYNC STROBE is asserted. The DCL is now set up to detect the
sync byte from the sync byte decoder. In the interim, SNI READ ENABLE enables serial shifting of data from the
disk into the shift register. When the logic recognizes the sync byte, the signal SN7 SYNC CLR is asserted.
SN7 SYNC CLR resets the byte counter to initiate a byte count of the data field. It also enables the ring (word in)
counter to count serial data bits and assert EC5 WORD IN after a complete word has been shifted into the shift
register. Each time a word is shifted in, a sync clock is developed for the controller. During the data field a total of
256 sync clocks are generated.
SN7 SYNC CLR also asserts SN7 DATA ENVELOPE to allow the ECC logic to accept the data field. The data
envelope signal remains asserted throughout the entire data block transfer; SN8 EOB BYTE negates it, and asserts
SN7 ECC ENVELOPE. Under the ECC envelope the two ECC words are read off the disk to complete the ECC,
check. Four bytes later SN8 END ECC BYTE negates the ECC envelope.
If the ECC check of the 256 word data field is good, SN5 EBL is asserted by SN8 EOB W BYTE. If the ECC check
shows that a data error exists, EC3 DCK asserts to indicate a data check error and the error correction p,rocess can be
entered if the software so desires.
If no data check error is present, SN5 EBL asserts to signal the end of a sector transfer. Then EC9 RUN is sampled
to determine if the transfer is to continue. If the RUN line remains asserted, SN5 COM CONT sets off the header
search subroutine again. If EC9 RUN is not asserted, sig;nal SN5 RESET GO resets the GO FF and terminates the
command.

3-16

....f - - - - - HEADER

GAP - - - - -....1..- - - - - DATA

FIELD

EC0 BYTE ClK

SS0
HEADER FOUND

r---------------------r---------------------~~~r--------~~--------~

SN1
READ ENABLE - - - - - 1

~----------~:------------~'J~'J-----+-4-----,

SN1
READ SECTOR ______-\

SN1
SYNC STROBE _ _ _--I

SN7 SYNC CLR

-1L
II-I

- - - - - - - - - a . . ( j ~~-----+----4

SN1
SYNC ClK TIME

SN7
DATA ENVELOPE

~------------------~~(rJ--------~

SN7
ECC ENVELOPE

I
I

SN5 EBl

---i :.- 200 NSEC :
~ONSEC:
II

SN5 RESET GO

------'h~

DP6
SECTOR PULSE

11-2469

Figure 3-6 Data Field Timing - Read Data and Read Header and Data

3.10 HOUSEKEEPING COMMANDS
3.10.1 No Operation (No-Op) (drawing number RP04-0-21)
The no-op command does nothing within the DCL. When the GO FF is set, the RG3 NO OP command is decoded
from the data in the control register. When RG3 NO OP asserts, the GO FF is reset to terminate t~e command
sequence.
3.10.2 Read In (drawing number RP04-0-20)
The read in command sets the VV (volume valid) bit, clears the desired sector/track address register, clears the
desired cylinder address register, and clears the FMT, Hel, and ECI bits in the offset register. When the STO GO FF
is set, the RG4 READ IN command is decoded from the data in the control register. The command performs these
functions and also resets the STO GO FF to terminate the command sequence.
3.1 0.3 Pack Acknowledge (drawing number RP04-0-20)
The only function of the pack acknowledge command i:i to set the VV (volume valid) bit. When the ~TO GO FF is
set, the RG4 PCK ACK is decoded from the data in the control register. It asserts RG4 READACK RESET which,
sets the VV bit and terminates the command by resetting the STO GO FF.
3.10.4 NG Drive Clear (drawing number RP04-0-21)
The NG drive clear command clears the two ECC registers and asserts the master reset pulse. The mastler reset pulse
(RG4 MAS RES) does the following:
1.

Clears all three error registers.

Clears the AT A and COMP ERR bits in the status register.

Clears the diagnostic mode bit in the maintainability register.

When the STO GO FF is set, the RG4 NG DRV CLR COM is decoded from the data in the control register. When the
command is asserted, the ECC register is reset and RG4 MAS RES asserts to perform the functions previously listed.
The master reset pulse asserts RGO CLEAR GO which resets the STO GO FF to terminate the command: sequence.
3.11 BYTE COUNTER OPERATION (drawing number RP04-0-22)
The purpose of the byte counter is to count the bytes within each sector and provide outputs at Ispecific byte
counts. The outputs are used to time fields/gaps that make up each sector. The byte counter clock is derived from the
shift clock. The source of the shift clock is determined by the mode of operation and the command being executed.
3.11.1 Shift Clock Select
ECO SHFT CLK is the bit clock used to clock the data word register, the ring (word in) counter, the CR:C circuit, the
ECC circuit and the sync clock/byte clock generator. The clock is selected from one of three sources: the diagnostic
clock, the read strobe from the Drive unit, or the pha.se locked oscillator (PLO) from the Drive unit. If, in the
diagnostic mode, the diagnostic clock is used, then read strobe and the PLO are inhibited. If a read operation is in
process, SNI READ ENABLE selects the read strobe for the shift clock and inhibits the PLO. If a write operation is
in process, the PLO is used as the shift clock. The PLO frequency is cut in half by the three level syqchronization
and frequency divider network (12.9 MHz to 6.45 MHz). The 6.45 MHz clock also serves as the ~RITE DATA
STROBE used by the Drive unit to clock data into the Drive during a write operation.
3.11.2 Byte Count Development
ECO SHFT eLK clocks the byte clock generator. The generator is an end-around counter connected to recycle every
eight counts. Outputs from the generator are shown drawing number RP04-O-23.

3-18

The byte counter is a synchronous binary counter clocked by ECO BYTE CLK. The outputs of the counter are
decoded to generate SN8 BYTE 30, SN8 BYTE 39, SN8 BYTE 511/575, and other counts. SN8 BYTE 0 through
SN8 BYTE 15 are generated separately in the byte count shift register. A second, high order-shift register (when
enabled by SN8 BYTE 511/575) produces the EOB, END ECC, and EOB W bytes. The two shift registers are
clocked by ECO BYTE CLK in synchronism with the byte counter.
The byte counter is reset several times during a sector and these times vary according to the command being
executed. The counter is reset by SN6 BYTE CNT CLR and by SNO BYTE CNT SYNC CLR.
SN6 COUNT EN enables the byte eounter if one of the synchronous data commands or a sector command is in
progress, provided an implied or a mid-transfer seek is not being performed.
The counter is also enabled by SSO TRACK LD EN which asserts when the desired sector/track address register is
loaded. After the counter reaches byte 8, SSO TRACK LD EN is negated and the counter must be enabled by the
proper command.
3.12 ERROR HANDLING AND ECe HANDLING
3.12.1 Error Handling (drawing number RP04-0-34)
The error handling flow diagram illustrates how the errors are classified and what action is taken for each class of
errors. There are three classes of errors: Class B, Exception, and Composite. Class B errors (RGO CLASS B ERR)
include most of the errors in error register Oland any error in error registers 02 or 03. Errors in error registers 02
and 03 are caused within the Drive unit.
The following is a summary of the effects of the three error classes.
A Composite Error:

Asserts ATTENTION excl~pt during a command sequence.

Inhibits setting of GO FF.

Negates RG3 GT STO GO.

Inhibits the setting of RG3 ATA MAS RES by RG3 CONT REG WRT.

Sets error bit (14) in the status register.

An Exception Error will:
1.

Do everything a Composite error does.

Assert EXCEPTION to the MASSBUS.

A Class B Error will:
1.

Do everything an Exception error does.

Abort any synchronous data transfer by asserting SN5 CLASS B ABORT.

3-19

When the controller asserts Exception on the MASSBUS, SN5 EXC is asserted and immediately aborts the command
sequence. The EBL FF is also set terminating the command sequence.
3.12.2 ECC Handling (drawing number RP04-()"3S)
The ECC subroutine is entered when an error is detectedl in a sector data field and error correction inhibit (ECI) is
negated. A detected error is indicated by asserting EC3 DCK. (See Read Data and Read Header and Data Flow
Drawing, number RP04-O-10.) Drawing number RP04-O-35 shows the flow sequence leading to the assertion or
negation of EC3 DCK.
The serial data read from the Drive unit (MAO RD/WRT DATA) is shifted into the ECC shift register. The register is
enabled for the duration of the data envelope and the ECe envelope by EC3 ECC REG FDBKCTRL.
With EC3 ECC CORRECT ENA negated, the ECC register zero detect circuit is examined at the end of the ECC
envelope when EC3 DCK SPIKE ELIM asserts. If an ECI ZERO DETECT exists, EC3 DCK is negated signifying that
the sector data field is free of error. If an ECI ZERO DEFECT is not obtained, EC3 DCK is asserted indicating the
presence of an error in the data field. If RGI ECI is negated, the error correction process is entered by asserting
EC3 ECC CORRECT EN.
EC3 ECC CORRECT EN keeps the ECC shift register enabled and starts the N-Code counter. The error correction
code requires that the ECC shift register be clocked 38,347 times for the 18-bit mode (38,859 for the 16-bit mode)
before the actual data field begins within the register.
When the N~Code counter reaches this value, EC2 N CODE WRD HICNT is asserted and enables the ECC position
register which counts bits of the data field.
With EC3 ECC CORRECT ENA asserted, the ECC shift register zero detect circuit looks for an ECI ZERO DETECT
again. If the error is correctable (error bits confined to an II-bit area), a zero detect is sensed when the first error bit
is reached in the ECC shift register. EC3 ECC CORRECll ENA is then negated, stopping both the position register
and the pattern register. The position register contains the position of the first error bit in the data field and the
pattern register contains the pattern of the next 11 bits.
If the error is noncorrectable (error bits separated by more than 11 bits), no zero detect is obtained as the ECC shift
register reaches the end of the data field. The end of the data field is indicated by a count of 42,987 from the
N-Code counter. In this case, EC2 ECH is asserted indicating a noncorrectable error. The exit from the subroutine
occurs by as'5erting EC3 ECC READY.

3·20

CHAPTER 4
REPLACEMENT PROCEDURES

4.1 GENERAL

The only special replacement procedures required for the Deivice ControllDgic involves the DP hex printed circuit
board. When replacing this board, care must be taken to ensure that the dual-in-line rocker switches are set for the
same device address as that of the removed DP board. No otheir special replacement procedures are necessary.

4-1

CHAPTER 5
MAINTENANCE

5.1

GENERAL

Preventive and corrective maintenan,ce procedures for the DCL are carried out by using diagnostic programs.
Individual diagnostic tests, the circuits they exercise, and related test objectives are described fully in the
RJP05/RJP06 Moving Head Disk Subsystem Maintenance Manual. DECsystem-IO diagnostics, which perform the
same function for the PDP-I 0 System, are also available.

5-1

APPENDIX A
INTEGRATED CIRCUIT DESCRIPTION

When data enters the second cell, the transfer of any data
word from a full cell to the next empty cell is automatic
and is activated by an on-chip control. Consequently, data
stacks up at the output to the memory while empty
locations "bubble" to the input of the memory. The
throughput time from input to output of the Silo is from 0
to 32 J.1S (16 J.1S typical).

A.I INTRODUCTION
This appendix contains descriptions of some of the integrated circuits used in the RP05 and RP06. Where applicable,
logic diagrams, schematics, and pin connection diagrams are
shown.
A.2 3341 64-WORD X 4-BIT SERIAL MEMORY (SILO)
The 3341 Silo Memory operates in a first in/first out mode
(FIFO). The output rate is independent of the input rate
and asynchronous or synchronous operation can be
achieved.

When data has transferred to the last cell in the Silo,
OUTPUT READY (OR) is asserted high, indicating that
valid data is present at the output pins (MO through M3 on
each chip). Data is not shifted out of the Silo, however,
until the OUTPUT READY and SHIFT OUT signals to the
Silo are both asserted high. When the data is shifted out,
OUTPUT READY goes low.. The output data is maintained
until both OUTPUT READY and SHIFT OUT go low. At
this point, the contents of the previous memory cell (if it is
full) are transferred to the output cell, causing OUTPUT
READY to be asserted high again. When the Silo memory is
emptied, OUTPUT READY stays low.

The four data inputs (DO through D3) are transferred to the
first' memory location if both the Input Ready OR) and
Shift In (SI) signals are asserted high (see Silo Memory
Block Diagram). After 250 ns to allow the data to stabilize,
IR goes low. However, data remains in the first memory
location until both IR and SI are brought low. At this
point, the data propagates to the next memory location, if
the location is empty. When the data is transf~~rred, IR goes
high, indicating that the device is ready to accept new data.
If the memory is full, the IR signal remaill1s un asserted
(low).

Table A-I lists the minimum, typical, and maximum times
for the above mentioned signals at 0° C and at 70° C.

Table A-I
Control Signal Timing Specifications

(t
Signal

MIN

TYP

Input Ready High Time
Input Ready Low Time
Data Input Stabilizing Time
Data Output Stabilizing Time
Output Ready High Tim e
Output Ready Low Tim e

300
400
250
250
250
450

138
-

90
170

A-I

70°
MIN

TYP

MAX

155

300
400
250
250
250
450

450
520
400
400
350
650

MAX

155

64 WORD x 4 BIT SILO MEMORY

DATA
INPUT

INPUT 2
READY 4--'-~---I
SHIFT ---,=,3~_ _...
IN

SILO
INPUT
STAGE
(I)

MAIN SILO
REGISTER
(62)

INPUT
CONTROL
LOGIC

MAIN REGISTER
CONTROL
LOGIC

SILO
OUTPUT
STAGE

DATA
OUTPUT

(I)

15
OUTPUT
CONTROL
14
LOGIC
t------+-.....:.....:..-

SHIFT OUT

.. OUTPUT READY

VGG
INPUT
READY
SHIFT IN

9
MASTER
RESET

SHIFT OUT

OUTPUT
READY
MO

VDD

PIN CONFIGURATION FOR EACH 3341
SILO CHIP

A-2

VSS

11-2426

The 7442 BCD-to-decimal decoder features familiar
transistor-transistor-Iogic (TTL) circuits with inputs and
outputs that are compatible for use with other TTL and
DTL circuits.

A.3 7442 4-LINE-TO-IO-LINE DECODERS (I-of-IO)
These monolithic decimal decoders consist of eight inverters and ten 4-input NAND gates. The inverters are
connected in pairs to make BCD input data. available for
decoding by the NAND gates. Full decoding of valid input
logic ensures that all ou tputs remain off for all invalid input
conditions.

TRUTH T A1BLES

Decimal Output

BCD Input

D
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1

0
0
0
0
1
1

0
0
1

1
0
0
0
0
1
1
I

1
0

0
0
1
1
0
0
1
1
0
0
1
1

0
1
0
1
0
1
0
I
0
I
0
1

1
1
0
1
1
1
1
1
1
1
1
1
1
1
1

0
0
1
1
1
1
1
1
1
1
1
1
1
1
I
1
1

1
1
0
1
1
1
1
1
1
1
1
1
1
1
1
1

3
1
1
1
0
I
1
1
1
1
1
1
1
I
1
I
1

4
1
1
1
1
0
1
1
1
1
1
1
1
1
1
1
1

5
1
1
1
1
1
0
1
1
1
1
1
1
1
1
1
1

6
1
1
1
1
1
1
0
1
1
1
1
1
1
1
1
1

1
1
1
1
1
1
1
0
1
1
1
1
1
1

1
1
1
1

1
1
1
0
1
1
1
1
I

1
1

9
1
1
I
I
1
1
1
1
1
0
1
1
1
I
1
1

OUTPUT 0
INPUT AO-

A
OUTPUT 1

OUTPUT 2
INPUT BO-

OUTPUTS

INPUTS

B
OUTPUT 3

OUTPUT 4

INPUT

co-

OUTPUT 5

OUTPUT 6
3

GND

OUTPUTS

OUTPUT 7
" -0733

INPUT DO-

0
OUTPUT B
D

OUTPUT 9

" ~O734

A-3

A.4 7485 4-8IT MAGNITUDE COMPARATORS
The 7485 performs magnitude comparison of straight
binary and straight BCD (8421) codes. Three fully decoded
decisions about two 4-bit words (A, B) are made and are
externally available at three outputs.

TRUTH TABLE
COMPARING

CASCADING

INPUTS

NOTE

OUTPUTS

INPUTS

f--

A3,B3

A2,B2

A1, B1

AO,BO

A<B

A=B

A>B

A<B

A"'B

A3 > B3

A3< B3

A3 = B3
A3=B3

A2 > B2

A2 < B2

X
X

A3 = B3

A2 = B2

A1 > B1

A3 = B3

A2 = B2

A1 < B1

A3 = B3

A2 = B2

A1 = B1

AO> BO

A3 = B3

A2 ~ B2

A1 = B1

AO < BO

A3 = B3

A2 = B2

A1 = B1

AO = BO

A3 = B3

A2 = B2

Al = B1

AO = 80

A3 = B3

A2 = 82

A1 = B1

AO = BO

A>B
~-

H = high level, L = low level, X = irrelevant

::~-~-=OL==---r------r

~-------

r----------1======I
A>e

lAIA

eo IN 0-:.:.:.-+--+-++-81 IN o=:--t---t--++-

(A ... 81 IN

1111

Ace

AOC>----+---~,__~

eo C>----t-----.---L
191

--------=0
~--- -------~--

Pin (16) = Vee. Pin (8) ~ GND

- -

A.S 8223 2S6·BIT BIPOLAR FIELD-PROGRAMMABLE
ROM (32 X 8 PROM)

The 8223 is a TTL 256·bit read only memory organized as
32 words with 8 bits per word. The words are selected by
five binary address lines; full word decoding is incorporated
on the chip. A chip enable input is provided for additional
decoding flexibility, which causes all eight outputs to go to
the high state when the chip enable input jls high.

32 X 8 ARRAY

Vee = (16)
GND=(8)
( ) = DENOTES PI N NUMBERS
11-2382

A-5

A.6 8234 2-INPUT 4-BIT DIGITAL MULTIPLEXER
This device is a 2-input, 4-bit digital multiplexer designed
for general purpose, data selection applications. The 8234
features inverting data paths. The 8234 design has opencollector outputs which permit direct wiring to other
open-collector outputs (collector logic).

(1)

(2)

(6)

(5)

(10)

(Ill

(15)

(14)

v(:c • (\6)
GIW·(S)
( ) • DENOTES PIN
NUMBERS
11-2383

A·6

A.7 8242 EXCLUSIVE-NOR 4-BIT DIGITAL
COMPARATOR
The 8242 digital comparator circuit consists of four
independent Exclusive-NOR gates with each gate structure
having an open-collector output to permit multiple bit
comparisons. A 4-bit comparator network is formed by
connecting the independent outputs; such a network is
easily expanded by cascading the outputs.

j~ or F PACKAGE
14 13 12 11 10 9

I~ ~' ., "

Q PACKAGE

8
14

'2 ·2 A2

AO 80 '0 f, 8, A1GND

1l!34567

"-0474

I
I
I
I
I
I
I

(

I
I
I
I

I
I

TRUTH TABLE

,
,
, ,

0
1
0
1

0
0

_.-J
fO

11-0472

A-7

A.8 74157 QUADRUPLE 2-LINE TO I-LINE
MULTIPLEXER
The 74157 quadruple 2-line to I-line multiplexer features
buffered inputs and outputs. All outputs are low when
disabled (enable high). The truth table and logic diagram
are shown below.

INPUTS

OUTPUT V

OUTPUTW

SN54174157,
ENABLE SELECT A B

SN54S174S157

SN54S174S158

X X

L X

H X

X L

X H

= high level, L = low level, X = irrelevant

1AO(2)

(3)

(5)

(6)

(14)
3A
(13)
3B
4A

(11)

(10)

SELECT

Pin 16 = Vee, Pin 8 = GND
ENABLE n;......-----0(']1

Pin (16) = Vee, Pin (8) = GND

A-8

A.9 74174 HEX D-TYPE FLIP-FLOPS

The 74174 contains six flip-flops with single outputs. The
flip-flops contain direct clear inputs and buffered clock
inputs.

INPUT
In

OUTPUTS
In+ 1

_--2-

tn = Bit time befo're clock pulse.
tn+1 = Bit time aiter clock pulse.

A O_ll_I_ _ _ _ ._ _ _~OA

121

8 0_14_1_ _ _ _ ._+-+--t08

1!l1

161
cO---------4-4-~

1111
00___- -_ _ ·

1131

E O--------~~--t

1141
0---------t--i--t OF

CLOCK"""--~-""

Pi" (145) = Vee. Pin (8) = GND

A-9

171

1101

1121

11!11

A.IO 74175 QUAD D-TYPE FLIP-FLOPS
The 74175 contains four D-type flip-flops with dual
outputs. Each flip-flop has direct clear and buffered clock
inputs.

INPUT

141

OUTPUTS
In + 1

0
H

(121

c 0-.-----+-+-1

tn = Bit time before clock pulse.
tn+l = Bit time after clock pulse.

Pin (16) = Vee. Pin (8) = GND

A-IO

A.II 74180 PARITY CONTROL C:iENERATOR/
CHECKER
The 74180 is an 8-bit parity generator/ chc,cker featuring
odd and even outputs and control inputs to provide odd or
even parity operation. Word length i.s e:xpandable by
cascading. The truth table, pin connection diagram, and
functional block diagram are shown below.

Vee

I NPUITS --------\

0
TRUTH TABLE
OUTPUTS

INPUTS
IOF ,'SAT EVEN
o THRU 7

6
7

EVEN ODD
I
INPUT INPUT EVEN

ODD

EVEN

0
0

ODD

EVEN

ODD

I
EVEN

I
ODD

,
,

0
0
1

X= IRRELEVANT

~
INPUTS

EVEN ODD I·EVEN I·ODD GND
INPUT INPUT OUTPUT OUTPUT

IEVEN
OUTPUT
DATA
IN PUTS

:~---v

IODD
OUTPUT

;~
ODD
IN PUT 0 > - - - - - - EVENo~---------

INPUT
11-2384

A-Ill

A.12 74193 4-BIT BINARY COUNTER
The 74193 binary counter has an individual asynchronous
preset to each flip-flop, a fully independent clear input,
internal cascading circuitry, and provides synchronous
counting operations.

COUNT UP

COUNT DOWN

LOAD

MODE

Parallel Load

CLOCK

Count Up

CLOCK

Count Down

H = high level, L = low level, X = irrelevant

Signal/Pin Designation
Signal Name

Pin Designation

DATA INPUT A
DATA INPUT B
DATA INPUTC
DATA INPUT D
CLEAR
LOAD
DOWN COUNT
BORROW OUTPUT
CARRY OUTPUT
UP COUNT
OUTPUTQA
OUTPUT Q B
OUTPUT Qc
OUTPUTQn

A·12

15
10

9
14
11

4
13
12

5
3
2

6
7

DATA
INPUT A

DOWN
COUNT
UP
COUNT

DATA
INPUT S

SORROW
OUTPUT

CARRY
OUTPUT

o---{>oo---{>o-

OUTPUT 0A

OUTPUT Os

DATA
INPUT C

OUTPUT 0c

DATA
INPUT D

CLEAR

o-----(:>o-f
OUTPUT 0D

LOAD

A-I3

A.l3 74197 SO MHz PRESETTABLE DECADE AND
BINARY COUNTERS/LATCHES

when the count/load is low, but will remain unchanged
when the count/load is high and the clock inputs are
inactive.

This high-speed monolithic counter consists of four dc
coupled, master-slave flip-flops which are internally interconnected to provide a divide-by-two and a divide-by-eight
counter. The counter is fully programmable; i.e., the
outputs may be preset to any state by placing a low on the
count/load input and entering the desired data at the data
inputs. The outputs will change to agree with the data
inputs independent of the state of the clocks.

During the count operation, transfer of information to the
outputs occurs on the negative-going edge of the clock
pulse. It features a direct clear which, when taken low, sets
all outputs low regardless of the states of the clocks.

This counter may also be used as a 4-bit latch by using the
count/load input as the strobe and entering data at the data
inputs. The outputs will directly follow the data inputs

J OR N DUAL-iN-LiNE OR
W FLAT P/ICKAGE
(TOP VIEW)*

D/ITA iNPUTS
r-~
Vcc

CLEAR

CLOCK
I

~:...,

°A

CLOCK
2

GND

DATA iNPUTS

ASYNCRONOUS INPUT: LOW iNPUT TO CLEAR SETS 0A
0s.Oc AND 00 LOW.

"Pin assi9nmenls for Ih ... circuits are Ihe lame for all packa9u.
11-0482

SN74197 TRUTH TABLE
(See Note A)
Count

Output
Q
QC
B

QD
L
L
L
L
L
L
L
L

L
L
L
L
II

L
L
L
L

H
H
H
H
H
H
H

0
1
2
3
4

5
6

8
9
10
II
12
13

H
H
H

L
L

H
H

L
L

L
II

H
L
L
H
H
L
L

H
H

H
L

NOTE A: Output Q A ::onnected to clock-2 input.

A·14

PRESET
CLOCI( 1 0------,-,---+--+---,

DATA S

-4------("IT

0-------,---4---I-~

PRESET

Os
CLOCK 2

0----------+-+---CLEAR

DATA C

O-------,--~--I-~

DATA D o - - - - - - - - - - - i f . - + _ - I

11-0411

A-IS

Reader's Comments
RPOS/RP06 DEVICE CONTROL LOGIC
MAINTENANCE MANUAL
EK-RPOS6-MM-OOI

Your comments and suggestions will help us in our continuous effort to improve the quality and usefulness of
our publications.

What is your general reaction to this manual? In your judgment is it complete, accurate, well organized, well
written, etc.? Is it easy to use?

What features are most useful?

What faults do you find with the :manual?

Does this manual satisfy the need you think it was int1ended to satisfy?
Does it satisfy your needs?

_____________ Why? _________________________________________________

Would you please indicate any fa(;tual errors you have found.

Please describe your position.
Name

Organization

Street

Departmen t

City _________________,. State __________________ Zip or Country

-- -- -- -

Fold Herle -

Do Not Tear - Fold Here and Staple -

-- -- --

FIRST CLASS
PERMIT NO. 33
MAYNARD, MASS.
BUSINESS REPLY MAIL
NO POSTAGE STAMP NECESSARY IF MAILED IN THE tJNITED STATES
Postage will be paid hy:

Digital Equipment Corporation
Techninll Documentation Department
146 Maill Stn'l't
Maynard. Massachusetts 01754

DIGITAL EQUIPMENT CORPORATION

~DI~DDmD WORLDWIDE SALES AND SERVICE

MAIN OFFICE AND PLANT

u.s A f)17S4· Telephone Fr<)1T fv1f~'''.{; ..' ,!.J/1 I" ',If)!! Ij.lt) fJfJ(](). I h(!wiJc!" (611) 897-f:)/I1 ."

M;JYllillc1 Mi1:;:;,"jc:!w<;elts

ilVX

ill; :·1/ Ii;!;) C,'/lle :;:C;dil.!.... M/IYN

if'I'~.(

DOMESTIC
NORTHEAST

MID-ATLANTIC (cont.)

WEST

CENTRAL (cont.)

"13/// Cr(!11Jlfl('ld Hndd
, )I,

1,<l~ l

,. 'jl,!!1! <' Id

~Vh, 111<;.111

,1Il0 I~,

O,]tapl1O(1('

313 S57 3063

MID-ATLANTIC

CENTRAL

:Prsl'y0884(
Dataphone 201-!l4R 0144

INTEnNATIONAL
UNITED KINGDOM (cont.)

NETHERLANDS
Olljlt;d Equ,pn,plit N.V

CANADA

TIll: HAGUE
~,r V'l, ~5ton

n,·! "/.. ,k/Ttw
Telf!phone: !}4

BELGIUM
Dl'jlt;d Equlprnent N V /S.A

£3R1JSSErs
lOll niH' [)'A~rt(}'ri

GERMAN FEDERAL REPUBLIC
Olqit,,1 Equipment GmbH
. MUNICH
A MIH)n.;hen '.3, W.1!!~~'lstelT'r:fatz 2
TAI0ph<.ne 0811·3'1Q:11

10,m HrlJssels. RAlqilJIn

1 cllThonA 02 "392~;6

TelAx

ARGENTINA

25207

BUENOS AIRES
COilsln SA
VI( n"!y del Pin~. 4071
T(,lppholl(' :)/.-3185

T(·lex 524·:?26

BlJ~nos Aires

Tfllex 012-/284

ZC··29

NORWAY
Diqltill EqUipment Corp Arj

OS/.O

SAO PAULO

Tlondh,,"nSVf~lp.n 47
0..,1·) '), NorwdV
Tplf'flhnn .... 07/613 34 40

Trlp.x

19079 QEC N

/U (;IONAL orr ICE

DENMARK

1·16 ~A,lln ~:;trl'l'l M,IYIl.,rd. Ivl;lssachuselts 01754
r( kphonc (617) 897;)111
'-rom MelropoJII:m Banton, 646-8600
IINX 710:~17m1J10?1?
Clbl.! DJGITAL MAYN

nil/it;11 Fqlllpment Akll,~bo!.Jq

C!)prNI-lAGEN
H(~I'l'r iPVPC!
)~)OO

GENERAL INTERNATIONAL SALES

fiB
Il(·ilt!rtJp. Df~nm.llk

A/T'bnex SA
RlJa rup'. S3S
San PnlJlo - SP
Telephone 52 7flOfi/1870 ,51-0912

AUSTRALIA
1)l(jll,11 (qlJlpmpnl I\ustr,dld Ply

I trl

A/)I i !l./IJF
f\,1"ntr(l<;" i\'/l'fllH'
.. N"IW"Il·1 '<'l)lh 1\1J~!r"I'd ',061

UNITED KINGDOM

I .,I,'ph l j'1<!

Il)ilj·1) 1T1~1

790-fj?B2~J

I (! Ip.x

INDIA
BOMBAY

/\II!:r.dld400f)

]!l(j,10GII)

Hmdllron Computers Pvl, ltd
69/A. I. l<tgmohandas Mllrg
l3ol'lbay-6{W8) India
Telf!phol1'~ 3H·1G15 36·S~~4
Cable TEKHIND

Telex 011-2594 PIE!nty

MEXICO
MfXICO CITY
Milll()IIr?NI
"'11<

'-, I ~!, ~,.1"lb'"dll'

VIc\Ofld

;'ii-<III

ITALY

PHILIPPINES

])1,:,',11 Iq'ill'lll I'! ';pf,
".·I!1'\I'J
{;,.I',,,t;,lIil)"{!J,l'J

Telt!ph,jne

3;J()'J

Mexitek, SA
l-u~wniH 40B Deplos 1
Apda Pastil I 12-1012
Ivk'(ICO 12. 0 F
rel/~phom~ (90:)) 536-09-10

MANILA

;ji,·lfv1,I.;I'(J

(02) 879 051/7/3/4/5

Stanford Computer Carpqratlon

I!,·I{
Tpl~.(

843-33615

M;J(i!lrllfi

PO Bux 1608
416 DaSIll<lrinilS St
rell'phorw 49-68-96

C'HfJ<Jf,Jtion Ltd

FrIIQIH' 1.lrrf'!.

rf'I.·;( 27?4q

NEW ZEALAND
[\"IIL:I I q(;'1,u)",,! COfl~(1r.j1 'Ill Ltd

·\I)rKI.ANn
Slre(~t

~A,lrl t'f'stl'r M~? IJI1H

1"J,>; f:;6H666

printed in U.S.A.

!"lox 7471

105