Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols
EnvoyACP/XF Application Programming Manual–132179
3-30
NRM READ Procedure
The effect of a READ request depends on the type of station your application is
controlling and on whether any received frames are present in the input buffer:
For a point-to-point primary or multipoint supervisor station, the EnvoyACP/XF read
unit for the line either initially enables the first READ request or the CONTROL 13
request that sets NRM. Thereafter, EnvoyACP/XF automatically enables and disables the
read unit, as appropriate.
For a point-to-point secondary or multipoint tributary station, a READ request initially
must enable EnvoyACP/XF’s read unit for the line. Thereafter, EnvoyACP/XF
automatically enables and disables the read unit.
Standard I-Frame Acknowledgment
Using the standard procedure for I-frame acknowledgment, a supervisor station receives
an I-frame with the poll-final bit set and immediately sends back an RR-frame with the
poll bit set to acknowledge the received I-frame.
The example in Figure 3-8
assumes the presence of two tributary stations (address 01
and address 02) and shows the standard procedure for I-frame acknowledgment.
Type of Station Effect of a READ Request
Multipoint supervisor When no received frames or WRITE requests are queued, READ
initiates the polling process.
Subsequent READ requests are queued and completed as the
multipoint supervisor receives frames from the remote stations.
Multipoint tributary If no received frames are present in the input buffer, the multipoint
tributary queues and completes all READ requests as frames are
received from the remote station.
Point-to-point
(primary or secondary)
Same as multipoint tributary, above.