Envoy ACP/XF Application Programming Manual

EnvoyACP/XF Application Programming Manual–132179
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Asynchronous Balanced Mode (ABM)
Protocols
This section describes application considerations for the Asynchronous Balanced Mode
(ABM) protocols supported by EnvoyACP/XF. The protocols described here are High-
Level Data Link Control (HDLC) and Advanced Data Communications Control
Procedures Asynchronous Balanced Mode (ADCCP-ABM).
ABM Features
EnvoyACP/XF allows you to use HDLC or ADCCP-ABM to establish an ABM data
link between two combined stations. You can use ABM only for point-to-point
configurations.
ABM protocols permit the following line configurations:
•
Two-way alternate transmission (TWA)
•
Two-way simultaneous transmission (TWS)
•
Switched lines
•
Nonswitched lines
Combined stations share the link-management responsibility, alternately serving as the
primary and secondary station. When operating in ABM, either station can transmit to
the other without first seeking permission.
Each combined station can act as both a primary and secondary station simultaneously
and each function has its own address. The primary/combined address transmits
commands, and the secondary/combined station address transmits responses.
Command and Information Frames
Transmitted by Local Station
Response Frames
Transmitted by Local Station
Always contain first configured station
address (primary)
Always contain second configured station address
(secondary)
Defaults to address 01 Defaults to address 03
Note. You cannot use the same address for the primary/combined station on both sides of the
link. For example, you could specify one primary/combined station as 01 and the other as 03.
If both sides of the link are NonStop Tandem systems, you cannot use the default address for
both sides of the link.
For basic address formats (1-octet length), you can change the configured station addresses
by issuing the SETMODE 17 procedure call.