Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols
EnvoyACP/XF Application Programming Manual–132179
3-33
NRM WRITEREAD Procedure
WRITE operation completion depends on the type of frame being sent:
For multipoint stations, the station index in the MCW of the application-level WRITE
buffer must not change until all WRITE requests to the same station are completed. That
is, for a multipoint line, the EnvoyACP/XF NRM protocols allow only one transmit
station address to be active at any given time. For example, if you issue a WRITE
request to station A while EnvoyACP/XF has one or more WRITE requests to station B
in the transmit queue, the request completes immediately with a CCL and a file-system
error 170.
If you issue a WRITE request within a multipoint supervisor station while the polling
function is in progress, polling halts long enough for frame transmission and
acknowledgment. Polling then resumes at the point where it was interrupted.
EnvoyACP/XF automatically enables and disables the write unit.
NRM WRITEREAD Procedure
EnvoyACP/XF interprets a WRITEREAD call as two separate requests: a WRITE that is
followed by a READ. Both operations use the same application buffer. The WRITE
request is queued first. After the associated frame has been sent and acknowledged,
EnvoyACP/XF queues the READ request. If any received frames are present in the
SDLC or ADCCP-NRM, dedicated input-buffer, the READ request obtains the oldest
one and completes.
Do not use the WRITEREAD call to send I-frames routinely. Restrict WRITEREAD
call use to special functions, such as sending your own unnumbered frames.
If you use full-duplex line facilities for Two-way Simultaneous transmission (TWS), file
system requests do not automatically complete in the same order at the link level as they
do at the application level. To have the application’s READ, WRITE, and WRITEREAD
requests complete at the application level in the same order in which they are completed
by the I/O process (of the link level), you must issue a SETMODE 30 call.
NRM CONTROL Procedure
Depending on the parameters that you supply in the call, the CONTROL procedure
regulates the Data Terminal Ready (DTR) signal, sets the station state, or requests the
transmission of certain command/response frames. Only one CONTROL call can be
outstanding at any time. For details, see CONTROL Procedure on page 4-2.
Sending I-frames The WRITE operation completes at the link level when the
remote station acknowledges the receipt of the frame.
Sending command/
response U-frames
The WRITE operation completes at the link level as soon as
EnvoyACP/XF sends the frame.
Note. If you issue a separate READ request after the WRITEREAD call but before the READ
portion of the WRITEREAD has been queued, the separate READ completes at the link level
before the READ portion of the WRITEREAD; that is, the separate READ obtains a frame older
than the read portion of the preceding WRITEREAD.