7. Delete (BA8421C) is removed from any in­ coming data stream because its transfer is
inhibited by the terminal control. However,
this character is included in the accumulated LHC characte r if the line is in text mode.
8. Idle (B8421) is removed from any incoming
data stream because its transfer is inhibited by the terminal control. However, this
character is included in the accumulated LRC character if the line is in text mode.
IBM Terminal Control Type II
This fcatllre I)rovidcs the controls necessar,Y for the nf 1 it:p11t stationc::; 8nri thp 10:12 output
printer at 600 baud. The transmission code is six
bits plus parity, with the following relation to the <3{)O ehannp1 interface: a 2 3 4 5 6 7 System! 360 Byte B A 8 4 2 C 1030 Code
B is the first bit transmitted onto the line following
the start bit.
A minimum of two stop bits will be transmitted
for every character; however, due to the unique
mode of operation of the 1031 input station, only
one stop bit is anticipated in receive mode (after
which the 2703 begins looking for the next start bit). Start B A 8 4 2
Check ;- C (Outgoing Data
Stop.! - - l Character
Each received and transmitted character is checked
for odd vertical parity. VRC errors will cause
Data Check to be set in the control-word sense field
bit will not cause termination of the current com­
mand. Unit Check will be set in the status field.
Polling and Addressing Polling of 1031 input stations is performed by Write
and Head commands or Poll and Read commands
issued under Start I/O. When polling, command
chaining should be uti1 i zed, so that the Read command
and allocated storage is ready for incoming data as quickly a:3 possible. .. fter the polling characters U)ro\"ided the program) arc sent out, chaining
occurs tu a Read command, and a three-second
timeout begins. The IBM Terminal Control Type IT pre-empts the 28-second timeout provided by the
common controls with the three-second short time­ oul bt'callse the line is in control mJde. Interruption
()j Ulf' program w ill occur if ® is received or it ti nH'uut occurs. Unit Exception \vill be set in the
unit status byte if ® is received. Unit Check will L' be set in the unit status byte if a timeout occurs, and
the Timeout bit will be set in the sense field. When
using the Poll command, the program is required to
follow each address with an index character, which
will be returned to the processor upon a positive
response from the terminal.
Addressing of 1030 output de\'ices (1033) is per­
formed by a Write command issued under Start I/O. The address characters © , ® ' and
terminal address are provided by the program. Command chaining to a Read command is utilized to
provide for receiving the ® or G> character. ® will set Unit Exception status to interrupt the
processor program, will cause the normal end,
which allows command chaining to a Write for the
output message. If no response is received, Unit Check is set in status, Timeout is set in sense, and
the command is ended.
Character-Recognition Summary
The following characters are recognized during
transmit operations:
1. ©, which. sets control mode in the control
word of the line.
2. @ , which sets text-out mode in the control
word when in control mode.
3. Pad character.
The following characters are recognized during
receive operations:
1. ®; which sets End in the control word.
2. @' which sets text-in mode.. (D is
recognized only if the line is in control mode
or poll mode; otherwise, it has no control
effect and is treated as a normal data character.
3. ®, which sets End and Unit Exception when
in control mode. End and Data Check are set
when ® is received in text-out mode.
4. Q:), which sets End in the control word of the
associated line.
5. Delete (BA8421C) is removed from any incoming
data stream because :'ts transfer to the control
word is inhibited by the terminal control.
6. Idle (B8421) is removed from any incoming data
stream because its transfer to the control word
is inhibited by the terminal control.
Telegraph Terminal Control Type I
This terminal control provides the necessary controls
for operating telegraph terminals under AT&T 83B2,
AT&T 83B3, or WU Plan 115A line control. The
transmission speed is either 45. 5, 56.9, or 74.2
bps. One uf these speeds must be chosen. Trans­
mission code is Baudot, with the following relation­
ship to the System/360 channel interface:

o 23456 7 System/360 Byte S 2 3 4 5 Baudot "S" represents the case. A logical one identifies
upper-case; logical zero, lower-case. The 1 bit is
the first bit transmitted after the start bit.
Shifted-character-set conversion is provided as
standard. The shift characters are L TRS for "letters" (or "downshift") and FIGS for "figures" (or "upshift"). In addition, "unshift on space" is
provided as a standard-wiring optional feature of
this terminal control; "unshift on space" means
that the space character causes the line to go to
LTRS mode if transmitted or received. The terminal
control most be wired for "unshift on space" only
if the attached 83B2 or 83B3 and 115A teletypewriter
terminals have this feature installed; a combination
of Type I telegraph lines with and without this
feature is not permitted in a single 2703.
LTRS and FIGS characters are automatically
deleted from the received data stream, and the case
is remembered in the lines-control word. Space
characters are not deleted from the received data
stream (whether with or without the "unshift on space" feature wired in), but the LTRS case is then
remembered. A sixth bit, set by the terminal con­
trol, is added to the code to indicate case to the pro­
cessor. Data bytes transferred from the channel
will be in six-bit form. The terminal control will
remove the sixth bit and remember the case. A
change in case will automatically cause insertion of
the proper shift character (LTRS or FIGS) into the
outgoing stream. The terminal control will send
1. 5 stop bits and check for the presence of one stop
bit on receive. After the 2703 is reset, the line
will be in lower case.
Polling and Addressing
Polling and addressing of 83B2, 83B3, or 115A
terminals are performed by Write or Read commands
issued under Start I/O. When polling, command
chaining should be utilized so that the Read command
and allocated storage is ready for incoming data as
quickly as possible. After the polling characters
(provided by the program) are sent out, chaining
occurs to a Read command, and a two-second time­
out begins. The Telegraph Terminal Control Type I
pre-empts the 28-second timeout provided by the
common controls with its two-second short timeout
while the line is in sequence zero. Interruption of
the program will occur if a timeout completes. Unit Exception will be set in the unit status byte if
the EOT sequence is received. For this terminal
control, the EOT sequence is FIGS-H, LTRS (where
FIGS-H is the H character received while the line is
in upper case; that is, the last shift character
received before the H was "figures-shift"). FIGS-H
must be followed immediately by the letters-shift
character (LTRS) to complete the EOT sequence. Unit Check is set in the unit status byte, and the
Timeout bit will be set in the sense field if a time­
out occurs. However, note that when the program
sends EOT, it should send the three-character
sequence--FIGS-H, LTRS--because some teletype­
wrjter terminals will recognize only this sequence
as EOT. When addressing, command chaining to a Read
command is utilized to provide for receiving the "V" (or "M") response.
A time rut will set Unit Check in the unit status
byte and Timeout in the sense field as when polling,
to interrupt the processor program. A "V" (or "M") answerback will cause a normal end, which may be
used to command chain to the output message.
Terminal-to-Terminal Operation with Search
For terminal-to-terminal operation between two
terminals on the same line, the operation should
proceed as follows:
1. The sending terminal be polled to acti­
vate its tape reader (assuming it has a
message to send). This should be done in the
conventional manner with A Write command.
If the message is to be sent to stations on
other lines or if it is to be logged or processed
by the CPU, the first address on the tape
should be "AZ" , the CPU's own address.
Otherwise, the addre ss on the tape should be
that of the station on the same line to which
the terminal-to-terminal message is to be sent.
2. The Write command that sends the polling
characters should be command chained to the
Search command. The Search command
should have a byte count of two and the SLI (suppress length indication) bit should be OFF in its CCW. If the polled station has no mes­
sage to send, it will respond \vith "V", and the
command will be terminated with Channel End
and Device End status. Because only one b J te
is transferred to the channel (the "V" or "M '
reply), the channel causes a record-length
interrupt to the program. The program should
then proceed to poll the next station.
3. If the station had a message and the first
address is '1AZ", the "AZ" is transferred to
the processor under the Search, and the
command is then ended with Channel End and
Device End status. Because two bytes were
43