ACC HDLC-NRM (SDLC) User's Guide

Appendix B 63
SDLC Loop Mode Option
Introduction
TEST Command and Response
In Primary/Loop mode the HDLCNRM protocol will periodically issue a
TEST command with the P bit set to ‘0’ to each secondary station. If the
correct response (TEST response with the F bit s e t to ‘0’) is not received
within the T1 timeout period, the TEST command will be repeated. After
N2 repeat transmissions of the TEST command with no response
received the secondary station will be considered to be in the
disconnected mode.
The default value for the contents of the TEST command I-field is six
ASCII characters as follows:
“U TEST”
Thetestpatterncanbemodifiedtoanysequenceofupto6bytesbythe
use of a control write request to the termina l. T he format of the control
write request is as follows:
This request should be the first request to the terminal after it is
enabled.
TEST commands are transmitted to secondary stations in the “up” state
(i.e.afterasuccessfulSNRM/UAexchange)at60secondintervals.The
Information field of the TEST response is not verified.
Bytes
Request Type (=1)
Data length (less than 7 bytes)
TEST data