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Data Communications
Table 7-7. Summary of Block Protocol Control Characters (Continued)
TEXT-IN
TEXT-OUT
RECEIVED
TRANSMITTED
RECEIVED
TRANSMITTED
Sent by CPU as a response
Sent by terminal as a
to an ACK received from
response to an ACK
terminal.
received from CPU.
CPU has no more TEXT to Terminal has detected CPU has decided to abort Term has no moreTEXT
to
xmit to terminal.
data overrun. This is a terminal xmission.
send to CPU or has just
permanent condition, as
received an ttRVI".
the size of the transmis-
sion exceeds the size of the
terminal input buffer.
CPU requests terminal
Term requests CPU
send last TEXT response.
retransmit last response
to TEXT.
Terminal acknowledges CPU acknowledges last
last text block and re- TEXT block & requests
quests the CPU to stop term send ttEOT".
sending ( . ) .
Terminal tells CPU that CPU tells term that last
last TEXT block was TEXT that term sent was
received OK.
OK.
Term acknowledges last CPU acknowledges last
TEXT block received is TEXT
b~
.k sent by term,
OK, but now term has no but tells term to wait be-
more buffers & cannot ac- cause CPU does not have
cept more TEXT.
any more buffs.
Term detected error in last CPU detected error in last
TEXT block CPU sent. In- TEXT block term sent. In-
valid VRC/BCC, etc. This valid VRC/BCC, etc.
includes temporary buffer
overrun, where size of
transmission does not ex-
ceed size of terminal input
buffer.
CPU is temporarily out of
Term is temporarily out of
text. The terminal must
data.
respond with a NAK.
7-41
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