IBM 3745 Maintenance Information Reference page 510

Modem Interface Management
X.21 Modem Retrain
Time-Out Values
On X.21 lines, modem retrain is entered when a DCE uncontrolled not ready or
DCE controlled not ready steady state is detected. When this occurs:
1. The CSP microcode starts a 20 second timer.
2. The FESH continues any transmission until the end of message is reached.
3. If a transmission 'is in progress when the retrain starts, the following ending
status is sent to the CCU when the transmission completes:
• SCF
=
X'22' (underrun/data transmitted)
• SCF
=
X'20' (underrun)
• SES
=
X'80' (modem retrain)
• LCS
=
X'OO'
4. If data reception is in progress when the retrain starts, the incoming frame
is flushed (to avoid filling the NCP buffers) and the receive command is
ended with the following status:
• SCF
=
X'04' (end of message)
• SES
=
X'10' (data check)
• LCS = X'OO'
5. If the DCE does not return to a 'ready' or 'ready for data transfer' state
before the time out expires, the following ending status is sent to the CCU:
• SCF bit 3
=
1 (modem check)
• LCS = X'EE'
The following is a list of the various timer values used by the HSS along with
their sources:
Enable time out
Disable time out
Reply time out
Taken from the set mode data, it is used during enable
command execution and also during transmit command
execution (to monitor CTS, if it is down).
Taken from the set mode data, it is used during disable
command execution to allow the modem, time to respond
to the changes on the modem-out leads.
Taken from the set mode data, it is used during receive
command execution to monitor for a reply to a trans-
mission.
DSR confirmation A MOSS init value, it confirms a steady state on DSR for
the stated period.
X.21 modem retrain A fixed 20-second value.
V.35 modem retrain The enable time out value is used if it is less than or
equal to 25.2 seconds. A retrain timer of 25.2 seconds is
forced if the enable time out exceeds this value. If the
enable time out is not a multiple of 400 ms, the modem
retrain timer is rounded to the next 400 ms increment.
See examples next:
Chapter 6. High Performance Transmission Subsystem (HPTSS)
6-29