Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols
EnvoyACP/XF Application Programming Manual–132179
3-13
Establishing and Controlling a Data Link
Mode, the primary-station application issues a CONTROL 14 call. In a primary station,
this call sends a Set Initialization Mode (SIM) command frame to the secondary
stations. In a supervisory station, the CONTROL 14 function uses the auto-poll
capability of EnvoyACP/XF to send a SIM frame to all tributaries.
In a secondary or tributary station, a CONTROL14 call sets the station so that it will
respond with a Request Initialization Mode (RIM) response to anything but a SIM
command.
When a command frame incurs an error, the CONTROL call continues through all
stations before it issues an error message (the error is reported for the first failing
station). The application then can issue READ(s) to determine which station or stations
caused the error. The CONTROL call does not stop when the error occurs unless the
error is a link failure. EnvoyACP/XF sends the mode-set command to all stations on the
link before EnvoyACP/XF terminates the CONTROL.
Establishing and Controlling a Data Link
The primary or supervisor station issues a CONTROL 13 call to send a Set Normal
Response Mode (SNRM), thus establishing a normal response mode link with a
secondary station. If the secondary station can accept transmissions, it responds with an
Unnumbered Acknowledgment (UA). If the secondary station cannot accept
transmissions, it responds to the SNRM with a Disconnect Mode (DM).
Standard Link Establishment and DM
When the standard link-establishment procedure is being used and the primary station
receives a DM in response to a SNRM (Figure 3-3), the primary station resends the
SNRM once. If the primary station receives another DM response, the primary station
places the nonresponding station(s) in an error-stop state and removes the station(s) from
the polling list.