transferred, .!lQ record-length interrupt occurs
and the channel can command chain to a Write to send the "V" answerback to the polled
station. This permits the station to start its
tape reader and continue to send the message.
4. If another reply to the poll is received under
the Search, the 2703 will scan the data on the
line until it recognizes the EOT sequence
(FIGS-H, LTRS), at which point it transfers
the "H" to the processor and ends the command
with Channel End, Device End, and Unit
Exception status. No transfer of data occurs
during this scan.
5. The Write command should then be command
chained to a Read to receive the message.
6. Line timcouts are active during execution of
the Search command. If the first address on
the tape begins with "A" but is not "AZ", the "A" will be transferred to the processor, but
otherwise the operation is normal; the "H" of the EOT sequence will be placed in the next
position in core storage.
Character-Recognition Summary The following characters are recognized during
write-type operations:
1. In LTRS mode, any character with the S bit ON causes the line to send the FIGS character
and set the shift bit before it is transmitted.
2. In FIGS mode, any cn'lracter with the S bit OFF causes the line to send the LTRS charac­
ter and reset the shift bit before it is trans­
mitted.
3. If wired for "unshift on space" operation, the
space character sets LTRS mode. In this
case, the S bit accompanying the space charac­
ter is ignored.
The following characters are recognized during
read-type operations:
44
1. A "V" (or "M") received as the first character
w ill set End status.
2. FIGS-H, LTRS received as EOT (end of trans­
mission) sets End and Unit Exception status.
3. The two-character processor address "AZ", if received as the first two non-letters
characters of a message under the Search command, will set End.
4. LTRS (letters shift), which sets downshift (0 in the S bit) if the line was in Ufshift (1 in
the S bit). In any case, this terminal control
inhibits transfer of this character to the I/O channel, removing it from the incoming data
stream.
5. FIGS (figures shift), which sets FIGS mode if
the line was in LTRS mode, and has no effect
if the line was already in FIGS mode. In any
case, this terminal control inhibits transfer of
this character to the I/O channel, removing it
from the incoming data stream.
6. If wired for "unshift on space" operation, the
space character sets downshift (0 in the S bit)
when it is received. The space character is
thcn transferred to the I/O channel with its S bit zero.
Telegraph Terminal Control Type II
This feature provides the controls necessary for the
attachment of Teletype Corporation's Models 33 and
35 Teletypewriter terminals to the 2703. Operation
is point-to-point and, generally, on a dial-up basis.
The transmission speed is 110 bps, with an eight­
bit data code. The code employed is the eight-bit
data-interchange code with the following relationship
to the System/360 interface:
o 234 567 System/360 Byte
2345678 35 Teletype Code One start bit and two stop bits are transmitted and
received by this terminal control.
Identification answerback from the 2703 is handled
by the processor. Output messages may be of any
length or format. Input messages may be of any
length. However, certain format restrictions are
imposed due to the line control adopted by these
terminals. On input, or during read-type operations,
the following characters are recognized by the 2703; they cause termination of the I/O operation, with
subsequent interruption of the Communications IOCS: 1. WRU--"Who are you"--which causes End
status in the LCW. 2. XOn--"Transmitter on"--which causes End
status in the LCW. 3. XOff--"Transmitter off"--which causes End
status in the LCW. 4. EOT--"end of transmission"--which causes End
and Unit Exception status in the LCW. 5. The delete character (all Marks) is recognized
by the terminal control. Transfer of deletes
to the I/O channel is inhibited during all read­
type operations.
The Break signal may be detected during trans­
mission. If the receive-data lead at the data set is
at Space for two successive transmit-start times,
the write operation is term inated with Channe lEnd,
Device End, and Unit Check status, and Intervention
Required is set in the sense field.
World Trade Telegraph Terminal Control
This terminal control provides controls for opera­
ting WT teleprinter attachments at transmission
speeds of 50, 75, or 100 bps. The transmission
code is ITA2, with the following relation to the
I/o interface and the 2703 serial data field.
o 23456 7 ::'hut 5 2 3. 4 5 System/360 Byte Shifted Code S represents the case. A logical one identifies
upper case; logical zero, lower case. The one bit
is the first bit transmitted following the start bit.
Shifted character set conversion, a standard
feature, automatically deletes LTRS and FIGS char­
acters from the received data stream, notes the last
shift character received, and inserts a sixth bit in
the code set to indicate the case to the processor. On outgoing data, the S (case) bit is removed and
noted. A change in the S (case) bit automatically
causes insertion of the appropriate shift character
in the outgoing data stream before sending the data
character.
Attachment to the World Trade Telegraph Ter­
minal Control is point to point with contention.
For transmitting, the programmer inserts from
4 to 20 LTRS characters before the start of message
character (line feed) to insure that the terminal is
able to receive properly. If the terminal bids for
the line simultaneously with the processor, an echo
check occurs, terminating the write operation at the CPU. For receiving, the Prepare command is issued
to the terminal line to wait for the completion of
the first character from the terminal. Command
chaining to a Read command can be used to accept
the message. This terminal control does not have
a short timeout to pre-empt the normal 28-second
timeout.
Character Recognition
End of Transmission (EOT) format is FIGS, CHAR­
AcTER' LTRS, with the character assigned on a
per system basis. EOT sets channel end, device
end, and unit exception status.
End of block (EOB) format is FIGS, CHARAC­
TER, with the character assigned on a per system
basis. EOB sets channel end and device end status.
Message Restriction
Terminal to Processor:
1. The characters used in EOB and EOT must
not be the same.
2. A space character received by the 2703 will
not downshift (FIGS to LTRS) unless the "Un­ Shift on Space" option is installed.
3. Although text following t...H EOT or EOB is not
transferred to the processor, the receive
type command is not ended until the trans­
mission line is quiet for one character time.
Text immediately tollowing FIGS, CHARAC­
TERS, LTRS is lost. EOT must not be sent
between blocks of data.
Processor to Terminal:
The terminal control automatically inserts the
proper shift character in outgoing data when a
change of case is encountered.
44.1
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