IBM 2265 Manual page 39

I/O Channel Sequences
and Responses
SOH }
2845 Address Addressing
Printer Address Sequences
Write Printer Command (Hex
=
AO)
I
STX
Text
ETX
LRC
I
STX
Etc.
SOH EOT
SOH EOT
* Sets Printer Request.
**
I ndicates printer-buffer overrun.
I
1
1
I
I
I
)1
I
I
I
I
~I
I
I
I
I
I
I
No Response
I
2845 Sequences
and Responses
I
NAK*t
EOT*
Printer Printer
Not Ready Busy
I
I
No Response
ACK
NAK
f
I
ACK
I
EOT**
f
tlf Printer is both Not Ready and Busy, Not Ready is given priority.
f
See "Error Recovery Procedures" for further I/O channel responses.
Figure 12. Write Printer, Sequence/Response Diagram
is not in use as a result of a previous Write Printer opera-
tion and is ready to receive text. Assuming an ACK
response is sent by the 2845, the I/O channel may proceed
with the following sequence containing the message to be
printed: STX, text,ETX, LRC character. As text charac-
ters are received from the I/O channel, they are parity-
checked and stored in the 2845 printer buffer, starting in
position 1. After the ETX and LRC characters are received,
if no VRC or LRC error was detected, the 2845 responds
with ACK to the I/O channel. The 2845 does not transfer
the text to the Printer until the text is completely received
and parity-checked
by~the
2845. Therefore, the I/O chan-
nel must send EOT or SOH in response to ACK to initiate
the actual printing of the message by the Printer. EOT or
SOH also terminates the command operation.
PROGRAMMING NOTE: If another block of text is sent to the
Printer in lieu of SOH or EOT, the previous text remains stored in
the printer buffer, and is not printed out at this time. The text of
the second message is stored in the printer-buffer area immediately
following the preceding text. No printout occurs until an SOH or
EOT character is received by the 2845. Be sure that the total num-
ber of text characters does not exceed 240.
Principles of Operation 39