Texas Instruments 990 User Manual page 29
Dx10 hdlc communications package
Hide thumbs
Also See for 990:
- Operation manual (276 pages) ,
- Manual (211 pages) ,
- Installation and operation manual (122 pages)
Table of Contents
Advertisement
PRIMARY STATION
TRANSMISSIONS
FRAME TO
SECONDARY 1
POLL
FRAME TO
SECONDARY 2
POLL
COMMUNICATIONS LINE
Introduction
44----------~--------------=~=~
________________________________________ •
TO PRIMARY
L
..
SECONDARY
STATION 1
TRANSMISSIONS
SECONDARY
STATION 2
TRANSMISSIONS
2280120
RESPONSE
FRAME FROM
SECONDARY 1
TIME
TO SECONDARIES
RESPONSE
FRAME FROM
SECONDARY 2
Figure 1-6
HOLC Network Polling Sequence
The
HOLC
polling
software operates in a handshaking mode, that
is, a response is expected
to
each
frame
transmitted
by
the
primary
station.
(This requisite does not necessarily apply at
the higher levels.)
The primary station, therefore,
acts
as
a
central
controller
for
all
operations at the HOLC level.
The
primary station maintains a
sequence
count
of
the
number
of
messages that remain unanswered by a given secondary station at a
given
time
and
relates
this to the maximum number allowed for
that secondary.
This maximum number is termed a
"window
size".
It
varies
according
to
the
type of secondary station and the
software level.
Consider the following examples:
2 2 7 0 5 2 6 -9 701
1-17
Advertisement
Table of Contents
