ACC HDLC-NRM (SDLC) User's Guide

Protocol Specific Configuration
Protocol Configuration Values
Chapter 4 49
Select Word
T1R - T1 Timer Resolution
In the case of a primary station this bit determines the resolution which
applies to the T1 parameter as follows:
T1R Bit clear (0) - 100 Millisecond units
T1R Bit set (1) - 1 Second units
In the case of a secondary station this bit becomes the top bit of the “Poll
Timeout” parameter.
T1 - Poll Timeout
This parameter is used to set the T1 response timer for a primary
configuration or the Poll Timeout for a secondary configuration.
For a primary terminal, the T1 response timer value is set by a
combination of the T1R timer resolution parameter and the T1 poll
timeout value. The value of the timer should be chosen so that it is longer
than the time taken to transmit the longest I-frame. The T1 timer is
started after a frame with the poll is transmitted and is restarted after
each I-frame that does not contain the final bit is received. A detailed
explanation of the T1 timer processing is given in Chapter 3, “Response
Timer”.
The user may choose a value for the T1 parameter between 2 and 31. A
value of 1 is not recommended as it can lead to an arbitrarily low timeout
value. The default value for the poll timeout value (if both T1 and T1R
parameters are zero) is one second.
When choosing a value for the timer, care should be taken to ensure that
the internal rounding down of the timer value, which occurs at run time,
does not lead to a shorter than expected timer value. This can be
achieved by either choosing a higher resolution (100ms), if possible, or by
choosing a value of the T1 parameter which is one unit larger than the
minimum desired timer value.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
TIR T1 Frame size Window N2