Control Data 3228-A User manual

Reference/InstructionManual
CONTROL DATA@
3228-A/3229-A MAGNETIC
TAPE CONTROLLER

60100300
REVISION
A
B
C
(4-12-65)
D
(6-7-65)
Pub. No. 60100300
June, 1965
Record of Revisions
NOTES
Addition of 2 Parts
Lists as Appendices C and D.
Incorporation of Change Order 893 O. which advanced
the Product Designation to 3228/3229 - A04.
This
manual obsoletes all previous editions.
Table of Contents (iii), 1-1, 1-11 through 1-13, 11-31,
II - 32, II- 33, II - 35, II - 37, II - 39, II - 41, II - 42, II - 43,
11-45, II-47, 11-49,
II-51, II - 53,
II-55, 11- 62, 111-4,
III-9, A-11 and A-13 revised.
Updated Parts List (pages C-1 through C-6).
Address comments concerning this
manual to:
Control Data Corporation
Technical Publications Department
4201 North Lexington Avenue
St. Paul, Minnesota 55112
© 1965, Control Data Corporation
Printed in the United States of America
or use Comment Sheet in back of
this book.

CONTENTS
Part I. Description and Operation
Section 1. Introduction
Section 2. Description
Physical Description
Functional Description
Clear
Connect
Status
Select Function Codes
Format
Interrupt
Information Transfer
Data Conversions
Section 3. Operation
Switches and Indicators
Equipment Selection Switch
Longitudinal Parity
Write
Vertical Parity
I-I
1 .... 4
1-4
1-4
1-5
1-5
1-7
1-8
1-10
1-11
1-12
1-16
1-16
1-16
1-16
1-16
Interrupt 1-17
BCD 1-17
Part II. Theory of Operation
Section 1. Connect
Section 2. Function Selection
Section 3. Function Operation
(Format)
Section 4. Information Transfer
II-I
II-5
II-I0
II-21
Register Transfers During Write II-21
Register Transfers During Write
Reply II-26
Register Transfers During Read II-26
iii
Write Operation Sequence
(First Output Word)
Write Operation Sequence
II-31
(N ot First or Last Output Word) II -31
Write Operation Sequence
(Last Output Word) II-32
Write Operation Sequence
(Non-Stop) II-32
Write Operation Sequence
(Write Reply) II-33
Read Operation Sequence
(First Two Frames) II-41
Read Operation Sequence
(Not First Two Frames) II-42
Read Operation Termination
Sequence (End of Record) II-42
Read Operation Termination
Sequence (Not at End of Record) II-43
Reverse Read Operation
Sequence II-44
Suppress Assembly/Disassembly
Operation Sequence II-44
Section 5. Function Operation Motion
Directives
Skip Bad Spot
Write File Mark
Search Forward to File Mark
II-53
II-53
II-53
Search Backward to File Mark II-53
Backspace II-53
Rewind II-54
Rewind Unload II-54
Section 6. Program Conveniences
Interrupt Function
Status
Lost Data Condition During
Write
Lost Data During Read
II-62
II-65
II-66
II-66
Rev. C

Part III.
Maintenance Section 2. Logic Cabling III -1
Section 1.
Environmental Care
III-l
Section 3.
General Maintenance
Procedure
III -10
Appendix A.
Tape Synchronizer / Controller Glossary
Appendix B. 3228/3229 Operation in a 3400 or 3600
System
Appendix C.
3228/3229 Parts List
FIGURES
Part 1.
Description and Operation
2-23
Write Register
1-1
3228/3229 Control Panel
1-2
(One Channel)
II-25
1-2
3228/3229 Magnetic Tape
2-24
BCD Conversion
II-28
System
1-2
2-25
12-to-0 Conversion II-29
Part II.
Theory of Operation
2-26
Assembly Control
II-30
2-1
Connect FFs
II-2
2-27
Write Timing
II-35
2-2
Connect Operation
II-3
2-28
Flow Chart: Write Prepara-
tion and Write First Data
2-3
Connect Timing
II-4
Word Operation
II-37
2-4
Function Select FFs
II-6
2-29
Flow Chart:
Write Termina-
2-5
Function Reply / Reject
II-7
tion and Write Nonstop Oper-
ation
II-39
2-6
Function Select Timing
II-8
2-30
Read Timing
II-45
2-7 Clear and Release
II-9
2-;:H
Flow Chart:
Read Prepara-
2-8
Parity Mode
II-I0
tion and Read First Data
2- 9
Binary Mode Operation
II -11
Word Operation
II-47
2-10
Clear Operation
II-12
2-32
Flow Chart:
Read Termina-
tion (Not End of Record) and
2-11
Release Operation
II-13
Read Nonstop Operation
II-49
2-12
Density
II-14
2-33
Flow Chart: Read Termina-
2-13
200 BPI Operation
II-15
tion (End of Record) and
Read Nonstop Operation
II- 51
2-14
556 BPI Operation
II-16
2-34
Skip Bad Spot
II- 55
2-15
800 BPI Operation
II-17
2-35
Write File Mark II-56
2-16
Tape Motion Signals
II-18
2-36
Search Forward to File
2-17
Reverse Operation
II-19
Mark
II-57
2-18 Clear Reverse Operation
II-20
2-37
Search Backward to File
2-19
Data Transfer
II-22
Mark II-58
2-20
Disassembly Control
II-23
2-38
Backspace
II-59
2-21
BCD Conversion
II-24
2-39
Rewind
II-60
2-22
0-to-12 Conversion
II-24
2-40
Rewind Unload
II-61
iv

FIGURES (Cont'd)
Part II (Cont'd)
2-43
Inte rrupt on End of Oper-
2-41
Interrupt Select
II-63
ation
II-64
2-42
Interrupt on Ready
II-64
2-44
Interrupt on Abnormal End
of Operation
II-65
TABLES
Part 1. Description and Operation
3-2
Signal and Pin Assignments:
1-1
Assembly/Disassembly Byte
Input Cable 1II-3
Order
1-15
3-3
Signal Definitions 1II-4
1-2
Function Codes and Status
3-4
Signal and Pin Assignments:
Responses
1-17
Data I/O Cable
III-6
Part II.
Theory of Operation
3-5
Signal and Pin Assignments:
Control I/O Cable 1II-7
2-1
Connect Sequence
II-I
3-6
Data Channel Signals
1II-8
2-2
Function Codes
II-5
3-7
Critical Delay Table III -11
Part III. Maintenance
3-1
Signal and Pin Assignments:
Output Cable
III- 2
v

3228/3229 Magnetic Tape Controller

PART I. DESCRIPTION AND OPERATION
SECTION 1. INTRODUCTION
The CONTROL DATA)~ 3228/3229 Magnetic Tape Controllers are input/output devices
for a Control Data 3000 series Computer System (Figure 1- 2). Either controller can be
connected to one 3000 series 12 - bit data channel. The schem e of selection and operation
follows the method inherent in any 3000. series peripheral equipm ent. The controller
allows the data channel to select a particular tape handler and modifies and synchronizes
data flow. The controllers may use all 603, all 604, all 606, or all 607 tape handlers.
The 3228 may use up to four tape handlers, the 3229 up to eight. The tape handlers are
selected and operated by the exchange of requests and replies typical to the 60X tape
systems. The controller can read or write on one tape handler at a time. Search and
rewind functions of the tape handler free the controller or the data channel for other
operations. Operation of the controller using 603 or 606 tape handlers (as opposed to
the higher performance 604 or 607 tape handlers) is a programming consideration.
The 603 and 604 tape handlers move tape at 75 ips, the 606 and 607 at 150 ips. In
this manual, any time a delay period is mentioned by itself, it is common to either tape
speed. If a delay period is mentioned, followed by another delay period in parentheses,
the first delay period is for 150 ips and the second for 75 ips.
Whenever a page reference in this manual is given in parentheses, e. g. : (Page 6), it
refers to a page in the 3228/3229 Magnetic Tape Controller Custom er Engineering
Diagrams Manual (Pub. No. 60093700),
):< Registered trademark of Control Data Corporation.
I-I
Rev. C

0507
~
0501
l
6
LONGITUDINAL PARITY
0
0 0 0 0 0
7 6 5 4 3 2
0 0 0 0
BCD INT
VERT
WRITE
PARI TY
f t i i
0511 OSlO 0509 0508
Figure 1-1.
3228/3229 Control Panel
h~~1
~ L-...J
~~
~ __ 3_00_0 __ 5_E_R_IE~S~,_12_-_B_IT __ ~CONTROLLER
DATA CHANNEL
*
3228-4 TAPE HANDLER MAXIMUM.
3229- 8 TAPE HANDLER MAXIMUM.
603,604,606, OR 607
TAPE HANDLERS
1
Figure 1-2. 3228/3229 Magnetic Tape System
1- 2
[IJ
t
EQUIPMENT
N
(O -7)
* 3228
*
3229
SWITCH

Computer - Tape Handler operations are selected by computer EF codes and signals.
These control the following functions:
1) Connect (code and signal)
Data Channel
Controller
Tape Handler
2) Status (on status lines after connect)
3) Function - Format (code and signal)
Format
Release
Parity Mode
Density
Clear
Reverse Read '- Release Same (604/607 only)
Motion Directives
Rewind
Rewind
Unload
Backspace
Search Forward to File Mark
Search Backward to File Mark
Write File Mark
Skip Bad Spot
Interrupt
Ready and Not Busy - Release Same
End of Operation - Release Same
Abnormal End of Operation - Release Same
4) Information Transfer
Write (signals)
Read (signals)
5) Assembly/Disassembly or Character (signal)
1-3

SECTION 2. DESCRIPTION
PHYSICAL DESCRIPTION
The 3228/29 controllers may be mounted in a number of different cabinets and configu-
rations. The installation engineer can determine the accurate physical description
of an actual installation by using data from the 3200 Site Preparation Manual (Pub. No.
60090100). Description of the 3228/29 control panel is in Section 3, Operation.
FUNCTIONAL DESCRIPTION
CLEAR
Prior to initial use of the tape controller, the system should be cleared. There are
five possible ways of clearing the controller:
1) Clear Channel (100 J,Lsec)
This instruction clears all activity in the data channel and clears the tape
handler connection.
2) Clear (2 J,Lsec)
This instruction clears the tape handler connection but the controller remains
"connected" in the sense that Status signals are still available for the data
channel.
3) Release
This instruction clears only the connection for a connected tape handler (not
relevant in a 3228/3229 - used for compatibility).
The latter two Function instructions (Clear and Release) can only be used after the
controller is connected to a tape handler.
4) Power On MC
When power is applied to the 3228/29, all tape handlers connected are cleared.
Logic in the controller is also cleared, and no Status signals are available to
the data channel.
5) External MC
This clears all tape handlers connected and clears the logic in the controller.
No Status signals are available to the data channel after executing this operation.
Both Master Clear operations place the 3228/29 in binary format.
I-4

CONNECT
The computer sends a 12- bit Connect code over the data channel to the t~pe controller.
A manual Equipment Selection switch on the tape controller locks out all Connect codes
except the ones having the correct bit combinations in bits 9, 10, and 11. These bits
must match the switch setting on the 3228/29 or the processor will not make the connec-
tion. Bits 0, 1, and 2 may have octal values of 0 - 7. These bits determine with which
of the tape handlers the 3228/29 will communicate. Bits 3, 4, 5, 6, 7, and 8 are not
used. If none of the controllers or any other equipments physically connected to the
processor via data channels have the proper switch setting, or a parity error occurs
in the Connect code, an Internal Reject is generated by the computer.
STATUS
After the desired tape handler has been connected, it is usually necessary to check the
status of the handler before attempting any further operations.
Ready (XXXI)
A Ready indicator on the tape handler lights when it is in a Ready condition, i. e. J power
has been applied and the tape handler is in Automatic mode. When in Automatic mode,
the tape handler is controlled by the tape controller.
The Ready signal is not present when the tape handler is manually operated from its
control panel.
Read/Write Control (and/ or) Busy (XXX2)
This signal is present:
1) If the tape handler is Ready.
2) During and for 5 ms after any operation requiring tape motion (Read, \Vrite,
etc. ).
3) Whenever the data channel begins executing or is executing a Read/Write in-
struction.
This signal will not be present if:
1) The tape handler is not Ready.
2) The channel begins executing or is executing a Read/Write instruction, and/ or:
a. Lost Data has occurred in a previous operation.
b. Interrupt On Abnormal End of Operation has occurred in a previous oper-
ation and the Interrupt signal is still present.
1-5

Write Enable (XXX4)
This signal is present only when the file protection ring is on the tape reel. When this
signal is absent, it is impossible to write on tape, although information may be read
from the tape.
File Mark (XX1X)
This signal is present when the tape handler has searched for and located an End of File
Mark. It is also present immediately after writing an End of File Mark. This signal
drops when: (1) reading/writing begins on a new record, or (2) a Backspace, Search
End of File Mark Forward, or Search End of File Mark Backward operation is initiated.
Load Point (XX2X)
This signal is present when the tape is at Load. Point. The signal drops when tape
motion begins.
End of Tape (XX4X)
This signal is present when the End of Tape marker is detected. The signal drops when
tape has been rewound past the End of Tape marker.
Density (X1XX)
See table 1- 2
Density (X2XX)
See table 1- 2
Lost Data (X4XX)
This signal appears during a Write operation (Write signal present) if the tape control-
ler is ready to accept information but the Data signal from the data channel is absent.
When the Lost Data signal appears during a Write operation, tape motion stops. Further
Write operations are impossible until the Lost Data signal is cleared with a new Function
or Connect code.
The Lost Data signal also appears during a Read operation (Read signal present) when
the tape controller has data ready for output, but the Data signal from the data channel
is absent.
1-6

If the Lost Data signal appears during a Read operation, reading continues until the end
of the record. Further Read operations are impossible until the Lost Data signal is
cleared with a new Function or Connect code. (Any legal Function code listed in table
1-2 will clear the Lost Data signal. )
The Lost Data signal is meaningless when the tape controller is attached to a 160/160-A
via a 3681 adapter. However, this signal must be cleared if Read/Write operations are
to continue.
End of Operation (lXXX)
This signal indicates that an operation is completely finished.
Parity Error (2XXX)
This signal indicates that a parity error has occurred during a Read/Write operation.
This signal drops when reading begins on a new record. A Clear Channel instruction,
External Master Clear or a Power On Master Clear causes this signal to drop. The
Parity Error signal also appears when an End of File Mark is sritten or read in Binary
mode.
SELECT FUNCTION CODES
The following information refers to the Function codes used with the Function instruc-
tion, i. e., the lower 12 bits which specify the operation. An octal 0 or 4 in bits 3, 4,
and 5 of the Function code indicates format, an octal 1 in bits 3, 4, and 5 indicates tape
motion, and an octal 2 in bits 3, 4, and 5 indicates Interrupt.
The proper tape handler must be connected before a Function instruction can be issued.
If an error occurs in the Function code (assuming the proper unit is connected), a
Parity Error signal appears on a transmission parity error line and the computer issues
an Internal Reject after 100 usec.
Once a function (Backspace, Rewind, etc.) is initiated un a tape handler on a given
channel, it is possible to connect another tape handler on the same channel, perform
some operation on the second tape handler, and reconnect the first tape handler when
the operation on the second handler terminates.
I-7
Rev. C

FORMAT
Release (0000)
A Release code clears the existing unit connection for a tape handler.
Binary (0001)
A 0001 code allows all information to be written or read in binary notation. A parity
generator makes the total number of 1 bits odd in the transverse (vertical) direction on
a total of seven separate tracks on tape. The End of Record check character makes
the longitudinal number of bits in each of the seven tracks even. During Read or Write
operations, a constant transverse parity check is made. A parity error is indicated on
a status line if a vertical parity error is detected.
Coded (0002)
A 0002 code allows all information to be written or read in binary coded decimal (BCD)
notation. A parity generator makes the total number of 1 bits even in the transverse
(vertical) direction on the seven tracks on tape. Constant parity checks during Read/
Write operations are performed in the same manner as in binary format.
556 BPI Density (0003)
200 BPI Density (0004)
A 0003/0004 code permits all information to be written onto or read from the tape at
556/200 density.
Clear (0005)
A 0005 code clears all existing tape handler connections. It is desirable to issue this
code when the channel has completed all operations on one or more tape handlers.
800 BPI Density (0006)
A 0006 code permits all information to be written or read onto or from the tape at 800
density. (On 604/607 Tape Handlers only. )
Set Reverse Read (0041)
This code is used for a Revers e Read operation. (See Revers e Read section.) (On 604/
607 Tape Handlers only. )
Rev. C
1-8

Clear Reverse Read (0040)
This code clears the condition established by the 0041 Format code.
All of the Format codes (0000-0006, 0041, 0040) result in a Reject if attempted when the
Read/Write control is busy.
Rewind (0010)
A 0010 code rewinds tape at high speed (225-400 inches/second) to the Load Point. Any
further Rewind instructions will initiate an imm ediate Reply. A Load Point signal
appears on a status line when the operation is complete.
Rewind Unload (0011)
A 0011 code rewinds tape at high speed until all the tape is on the supply reel. All
further operations on this tape are locked out until the tape has been reloaded manually.
Backspace (0012)
A 0012 code backspaces tape one record length. If the Load Point occurs than at the
beginning of the tape, this code will backspace tape from Load Point to one record
length behind the Load Point.
Search End of File Mark Forward (0013)
Search End of File Mark Backward (0014)
A 0013/0014 code searches forward/reverse until an End of File :Mark is detected. A
File Mark signal appears on a status line when the operation is complete. If no file
marks are detected, tape motion continues until tape is completely off the supply reel.
Write End of File Mark (0015)
A 0015 code writes 178 as an End of File Mark (even transverse parity) in both binary
and BCD format. Writing an End of File Mark does not change the current format.
Skip Bad Spot (0016)
A 0016 code moves and erases tape 6 inches in a forward direction. If Interrupt On
End of Operation is selected, Interrupt will occur when the Skip Bad Spot operation is
complete.
NOTE
Codes 0010-0016 result in a Reject if attempted when
the Read/Write control is busy.
I-9
Rev. C

INTERRUPT
All desired Interrupt instructions must come before a Read or Write operation, but can
occur during any other operation. The Equipment Selection switch determines which
line the Interrupt signal is transmitted on. For example} if the Equipment Selection
switch is set to 5, any Interrupts coming from the controller will be transmitted on
interrupt line 5. Any new Interrupt instruction clears the existing Interrupt signal.
This signal is also cleared by releasing all three possible Interrupts or doing a Master
Clear.
Interrupt on Ready and Not Busy (0020)
Release Interrupt ob. Ready and Not Busy (0021)
The 0020 code allows a tape unit to send an Interrupt signal out on the channel when this
tape handler is in a Ready and Not Busy condition, i. e., when power is applied, the
unit is in Automatic mode, and all tape motion has ceased. Release Interrupt on Ready
and Not Busy code 0021 clears this condition.
Interrupt on End of Operation (0022)
Release Interrupt on End of Operation (0023)
A 0022 code allows a tape handler to send an Interrupt signal out on the channel
after:
1)
2)
A File Mark has been located in a Search File Mark Forward or Backward
operation
3) Load Point has been detected during a Rewind operation, or
4) A Skip Bad Spot operation has been completed.
Release Interrupt on End of Operation code 0023 clears this condition.
Interrupt on Abnormal End of Operation (0024)
Release Interrupt on Abnormal End of Operation (0025)
A 0024 code allows a tape unit to send an Interrupt signal out on a channel after an ab-
normal operation occurs. The abnormal operations are: End of Tape, File Mark, Load
Point, Transverse Parity Error, Lost Data, and Connected Tape Handler Becoming Not
Ready. In all but the last case, the Interrupt occurs when one or more of these con-
ditions is encountered and an End of Record check character is written or read by the
Rev. C
1-10

tape unit. In the case of Interrupt on Connected Tape Handler Becoming Not Ready,
Interrupt occurs immediately when the handler goes from a Ready to a Not Ready
condition (e. g., if someone were to turn off the power on the tape unit). Interrupt on
Connected Tape Handler Becoming Not Ready will not occur: (1) during a Connect oper-
ation or (2) when a 0000 Function instruction (Release Connected Unit) is being executed.
A new Read/Write operation cannot start until the Interrupt signal is cleared by one of
the methods mentioned previously in this chapter under the Interrupt section. Release
Interrupt on Abnormal End of Operation code 0025 clears this condition.
The processor will enter an Interrupt routine and process the Interrupt. A Stop Channel
Activity instruction (in the processor Interrupt routine) will terminate data channel
activity and store the present word count, etc. When the Interrupt signal is cleared
(in the processor Interrupt routine), reading may be initiated by a new Read instruction.
The processor will enter an Interrupt routine and process the Interrupt. When the
Interrupt signal is cleared (in the processor Interrupt routine), writing may be initiated
by a new Write instruction.
INFORMATION TRANSFER
Write
Mter the tape handler has been connected and format chosen, the programmer should
check status for a Write Enable (bit 2 in the Status Reply code). If this signal is not
present, the protective ring is probably missing from the tape reel. It is possible to
write on the tape only when this condition has been corrected. (If the Write Enable is
not present, the data channel hangs up.) If the Write Enable is present, accompanied
by the Ready signal, the Write operation may begin.
Read
In a Read operation, the order of events is similar to the Write operation. After con-
necting, checking status, and choosing the proper format, the Read operation begins.
It is not necessary to check for a Write Enable, since Read operations from the tape are
possible when the protective ring is not present on the tape reel.
During Read and Write operations, the programmer may choose to check status period-
ically. He may also program one or more Interrupts to let the computer know when
1-11
Rev. C

the present operation is complete.
Reverse Read (On 604/607 Tape Handlers Only)
The 322X can read information in a reverse direction from tape. Six-bit frames are
read from tape and assembled into 12-bit bytes and sent to the data channel. When a
word is read in a reverse direction from tape and entered into storage, it is identical
to the word which was initially written on the tape from storage. There is no change
made in the final order of the bits during a Reverse Read operation.
To initiate a Reverse Read operation (assuming format has already been selected and
all tape motion has stopped), a 322X controller must first receive the Function code
0041 (Reverse). When the Read instruction is executed in the processor, the Reverse
Read operation will begin. A Reverse Assembly signal will be sent to the data channel
from the 322X to indicate that the 12-bit bytes should be assembled in reverse order.
Transverse and longitudinal parity checking occurs as in a normal Read operation with
one exception: if the first frame read is a record check character, no vertical parity
check is made on that character. Vertical parity checking is performed on all remaining
frames.
If C\. Reverse Read is attenlpted from Load Point,
The Read
operation will halt indefinitely.
Parity errors and Interrupts may be handled as if the operation were a Normal Read.
An End of Record signal is returned to the data channel ~hen a record gap is reached.
If a Backspace function is selected during the time a Reverse Read format is selected,
the tape will "backspace" forward.
The Function code 0042 (Clear Reverse) should be issued when the Reverse Read oper-
ation terminates.
DA T A CONVERSIONS
Transmission Parity
All information transfer between the data channel and the controller uses 12 bits of data
and 1 parity bit (odd parity). The controller checks the accuracy of the parity bit during
a Write operation and generates the bit during a Read operation.
Rev. C
1-12

Illegal BCD
The tape handler generates a sprocket pulse whenever it senses a bit in a frame on the
tape. Therefore, if a 6-bit data character of all zeroes is written in BCD mode, the
tape handler will not recognize the frame and an error would occur. To prevent this,
the controller automatically converts a character of all zeroes to 128 when writing and
128 to all zeroes when reading. This makes 128 BCD an illegal number in relation to
the computer.
Assembly / Disassembly
Example I in table 1-1 shows the order in which the two characters in each data channel
word are written on tape. Example IV shows the order in which data on tape is assem-
bled to the data channel. Example V shows the assembly during a Reverse Read.
Suppress Assembly/Disassembly
If the Suppress Assembly/Disassembly signal is sent to the controller during a Write
operation, bits 6 through 11 of the Data Channel word are discarded and only bits 0
through 5 are written on the tape (table 1-1, examples II and II!).
If the signal is sent to the controller during a Read operation (forward or reverse),
bits 6 through 11 of the Data Channel input word are packed with zeroes (examples VI,
VII, and VIII).
Programlning Considerations:
1) If data is to be assembled from a tape that was recorded in Suppress Assembly/
Disassembly mode, assembly difficulties may be encountered. The problem
is that in Suppress Assembly/Disassembly mode, an odd number of frames
may be written on the tape. If this occurs, and the tape is read forward, the
controller will automatically fill in bits 6 through 11 of the last input word
with zeroes. If an odd number of frames are written, and a Reverse Read is
attempted, the inverted assembly will be one frame out of order and bits 0
through 5 of the last Data Channel word will be filled in with zeroes (table 1-1,
example IX).
2) If a Reverse Read is attempted in Suppress Assembly / Disassembly mode, the
check character may be read to the Data Channel as the last frame (first Data
Channel character). If no check character exists (check character = zero
because of an even number of bits in each tape channel), the last frame will be
read as the first Data Channel character (table 1-1, examples VII and VII!).
I-13
Rev. C