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Data Communications
Table 7-7. Summary of Block Protocol Control Characters
CONTROL
POLL
SELECT
RESPONSE
RESPONSE
STX-«TEXT" -ETB/ETX
Positive response to
POLL.
«EOT"
Negative response to
POLL. Terminal has no
TEXT to xmit.
tfENQ"
"RVI"
Terminal acknowledges
select, but requests the
CPU to stop sending
( . ) .
fl\CKO/ACKl"
Terminal tells CPU that it
is ready to accept TEXT
(ACKO).
rtWACK"
Term is temporarily busy
(term has no available
buffers). Cannot accept
TEXT.
rtNAK"
I
STX-GID-DID-CN-ETX
•
has been pressed.
I
STX-ENQ (rtTTD")
,
i
7-40
J
~
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