IBM 2265 Manual page 37

I/O Channel Sequences
and Responses
SOH }
2845 Address Addressing
2265 Address Sequence
Write Addressed DS Command (Hex
=
AD)
I
STX
Text
ETX
lRC
I
STX
Etc .
SOH
EOT
SOH EOT
... Useful in conversation mode to restore 2265 keyboard.
2845 Sequences
and Responses
I
No Response ACK
I
No Response ACK
I
NAKt
t See "Error Recovery Procedures" for further I/O channel responses.
Figure 10. Write Addressed DS, Sequence/Response Diagram
As indicated in Figure 10, the 2845 may also respond
to the text transmission by sending NAK. The NAK re-
sponse indicates that the 2845 detected either a VRC or
LRC error. When a VRC error is detected in a text charac-
ter, the Check symbol is displayed on the screen in place
of the character in error. The program may retry the trans-
mission starting with STX. (See "Error Recovery Proce-
dures".)
No response to text indicates that the 2845 did not rec-
ognize, or detected a VRC error in, a control character
(STX or ETX). The 2701 will time out and the program
must send SOH to re-establish the 2845 in control mode,
then reissue the c.omplete. addressing sequence and message.
Erase/Write Addressed OS (Figure 11)
The Erase/Write Addressed DS command sequence may be
addressed to Display Stations only. It1S essentially an
Erase command combined with a Write sequence. This
command causes the 2845 Display Control to erase the
message displayed on the screen of the selected 2265 Dis-
play Station and causes the cursor to be positioned in
the first character position (upper left corner of the screen).
Thus, it is assured that the message following the address-
ing sequence will be written on the screen of the selected
2265 beginning at the first character position.
Normal 2845 response to the Erase/Write addressing
sequence is ACK. The ACK response indicates to the I/O
Principles of Operation 37