count of the character is even, a logical zero if the
bit count of the character is odd.
Vertical redundancy check (VRC) and longitudinal
redundancy check (LRC) are provided. Any error
detected sets the Data Check bit within the sense
byte. A Data Check does not cause immediate
termination of the current command.
Polling and Addressing
Polling and addressing of the 1050, 1060, 1070, or 2740 terminals are performed by a Write and a Read
command or by a Poll command preceded by a
Start I/O instruction. When polling, command
chaining is utilized so that the Read command and
the allocated storage are ready to receive the in­
coming data. In the first case (a Write and a Read
command), on sending out polling characters (pro­
vided by the program), chaining occurs to a Read
command, and a timeout begins. At this point, the
IBM Terminal Control Type I pre-empts the 28-
second timeout provided by the common controls and
storage with its two-second short timeout. The 2703 interrupts the CPU program if a ® character
is received or if a timeout occurs. Unit Exception
is set in the unit status byte if ® is received. Unit Check is set in the unit status byte if a timeout occurs;
the Timeout bit is set in the sense field. Using the
Poll command, the 2703 will end the command with
the Status Modifier if a positive response is received
from the terminal. If no response, or an incorrect
response, is received, the command is ended with
Unit Check status and the appropriate sense indica­
tion. If all terminals have been polled and no posi­
tive response has been received, the command will
end normally. 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. To initiate a receive operation
from a 2740 or 2741, a Prepare command is followed
by a Read command; then, data transmission is
started.
During addressing, command chaining to a Read
command is used to provide for receiving the ® or ® character. ® sets Unit Exception in the status
byte, as in polling, to interrupt the CPU program. ! causes a normal end, which can be command
chained to the output message.
Character-Recognition Summary
The following characters are recognized during
transmit operations:
1. ©, which sets control mode and resets the
check-character (LRC) accumulator.
2. @' which sets text-out mode and initiates LRC accumulation. @ is recognized if the
line is in transmit direction and in control
mode or text-in mode. This character has no
control effect if transmitted while the line is in
text-out mode. (It is treated as a normal data
character. )
3. @ , which sets LRC sequence. Termination
of the Write command is initiated by ® .
4. In text-out mode and in downshift ( a 0 in the
shift bit), any character with the S bit ON causes
the line to send the upshift character and sets
a 1 in the S bit before being transmitted.
5. In text-out mode and upshift ( a 1 in the shift
bit), any character with the S bit OFF causes
the line to send the downshift character and
sets a 0 in the S bit before being transmitted.
6. A pad character from the channel causes all
marks to be transmitted for one complete
character time.
PROGRAMMING NOTE: For the ending sequence of any text
message, the ® and © must be in the same case. If not,
the 2703 will detect this as a change of case and will insert
a shift character ahead of the ©.
The following characters are rec ":gnized during read
operations:
1. ©, as end of transmission, which sets
control mode and End and Unit Exception status
in the address lines.
2. @, which is recognized when the subject
line is in control mode or poll mode and causes
text-in mode to be set and LRC accumulation
to be initiated. When in the receive direction,
and when not in control mode, @ is treated
as a normal data character.
3. ®, which sets the LRC control sequence.
The next received character will be checked
against the accumulated LRC before the Read
command is terminated.
4. ®, which sets End and Unit Exception when
in control mode. End and Data Check are set
when ® is received and the operation is in
text-out mode.
5. <l?, which sets End during control mode anc1 text-out mode.
6. Upshift, which sets upshift (1 in the S bit) if the
line was in downshift (0 in the S bit); if the line
was already in upshift or in control mode, this
character has no effect. In any case, the
terminal control inhibits transfer of this
character to the data word, removing it from
the incoming data stream, although it is
included in the accumulated LRC character
if the line is in text mode while receiving.
41

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: