Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols
EnvoyACP/XF Application Programming Manual–132179
3-44
NRM Nonswitched Point-to-Point
command or response. The applications must examine bits 3 through 7 of the MCW in
the read buffer to determine which command or response was received. For example, a
SNRM code in MCW.<3:7> is %20.
The link is now in NRM. In the primary station, upon posting a READ, EnvoyACP/XF
begins polling the secondary station by sending Receive Ready (RR) frames with the P
bit set. In the secondary station, EnvoyACP/XF automatically responds to the polls by
sending RR frames with the F bit set. The applications use the READ, WRITE, and
WRITEREAD procedures to exchange data.
Because the actual use of READ loops, WRITE loops, and WRITEREAD procedures
varies considerably from one application to another, the following line activity is shown
without a corresponding application-level code sequence. The diagram of line activity
shows what EnvoyACP/XF does at the link level in response to various I/O calls.
Transmission frames automatically generated by EnvoyACP/XF and the CLIP are
enclosed in brackets.
The following example shows typical line activity in NRM. After the primary station
posts the initial READ, EnvoyACP/XF begins polling the secondary station:
PRIMARY SECONDARY
[Nr(0),RR,P] —————————————>
EnvoyACP/XF
automatically
responds to
poll.
<—————— [Nr(0),RR,F]
[Nr(0),RR,P] —————————————>
<—————— [Nr(0),RR,F]
.
.
.
.