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EO T - Start Code
Answer-Back
(Cont'd)
RULES FOR PAUSE
AND BREAK
RECOGNITION
Pause
CCM Initialization
It
is not necessary to inform the program through CMs of the
presence of STX and ETX when transmitting data to a remote
terminal.
Since length of message is known, byte count will
lapse upon EOM; (ETX)
this. automatically generates a CM.
It
would not then be necessary to check in data block because NDB is
always valid during CCM transmit.
For systems employing merely a character parity check, only the
bad message CRB (parity error) is generated automatically as a
result of OW-I, bits 12- 9. Therefore, the good message CRB must
be specified by an OW generated CM if desired o Any appropriate
EOM indication can cause
access~o
an OW-l specifying in bits 12-9,
good message reporting. The CCM will then check for the setting of
the error bit, and in its absence, will report a good message. In sys-
tems utilizing block parity both indications are automatic and the
generation of a CM as a result of OW recognition is unnecessaryo
(See Data Accuracy Control, Section 10)
•
Pause and Break duration detection, where required by the particular
system involved, is implemented through the use of operational wordso
•
The three conditions under which Pause detection is normally required
are:
1.
When input from the remote device is generated as a result of
manual keyboard operation:
interrupted transmission is inherent.
Therefore, the processor does not want to be notified on these fre-
quent data lapses, nor does it want these Pause characters to enter
memory ..
In this case the operational word specifies the deletion of all- in-
coming Pause characters.
2. When input from the remote device is generated by an automatic tape
transmitter:
torn tape conditions can occuro In this case the pro-
cessor should be notified immediately through the generation of a
coordination message.
The operational word may be set to recognize a specified number of
sequential Pause characters,. up to four. The resulting coordination
message causes termination of the Read command to that buffer.
3. When a Pause of a certain duration is used for specific signalling
purposes, a coordination message is generated as a result of
operational word recognition.
The operational word is set to recognize the specific number of Pause
characters which create the particular signaL
2-14
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