ACC HDLC-NRM (SDLC) User's Guide

Using HDLC-NRM (SDLC) Protocols
Application Control Requests
Chapter 336
Application Control Requests
All HDLC-NRM (SDLC) terminals must be enabled prior to sending and
receiving of messages.
The enable request will cause the primary station to initialize the mode
for the terminal by sending a Set Normal Response Mode (SNRM)
command to the terminal. After the appropriate (UA) response, normal
polling will commence.
The enable request will cause the secondary terminal to respond to
commands from the primary station, such as SNRM and polls.
The activate request is used to allow the receiving of messages on a
terminal. Normally, an application will issue an activate request at the
same time it is enabled. The initial enabled state of the terminal will also
be activated. A deactivate request can be used to mark a terminal busy,
so that it is unable to receive messages. When a terminal is busy, it will
acknowledge polls and other frames with a Receiver Not Ready (RNR)
frame rather than the usual Receiver Ready (RR) frame.