ACC HDLC-NRM (SDLC) User's Guide

36 Chapter3

Using HDLC-NRM (SDLC) Protocols

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 t o

commands from the primary s tat ion, 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.