ACC HDLC-NRM (SDLC) User's Guide

62 AppendixB
SDLC Loop Mode Option
Introduction
Introduction
The SDLC loop mode of operation is described in the IBM document
“Synchronous Data Link Control General Information” GA27-3093. A
subset of this standard has been implemented. Only the primary station
is supported i n loop mode. The “turn-around” signal described in the
SDLC document is not used.
NOTE The SDLC loop mode is not available for use on the 2-Channel ACC
interface.
Frame Types Supported
In loop mode the HDLC/NRM protocol s upports the use o f the following
additional commands and responses:
Request to Send Control
In Primary/Loop mode the HDLC/NRM protocol maintains the RTS
signal in the ON condition.
Unnumbered Poll
InPrimary/LoopmodetheHDLC/NRMprotocolwillpollthesecondary
stations with the Unnumbered Poll (UP) command with the P bit set to
‘0’andwiththeaddressfieldsetto0xFF.
Commands Responses
SIM RIM
TEST TEST
UP