Texas Instruments 990 User Manual page 247
Dx10 hdlc communications package
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Communications Structures
Communications between primary station tasks and TM990
or
PMSSO
should be peformed in accordance with this appendix.
D.S.1
Network Information Table (NIT)
This
section describes the purpose of the destination and source
IDs and how they are used by the primary station software.
A Network Information Table (NIT) in the primary station includes
the information required to route messages from
primary
station
tasks to secondary station tasks or devices.
There are two table
formats
defined.
The
long form is an output format, the short
form is an input format.
The input format is refered to
as
the
short
form
because it includes the minimum information required
to route input messages to tasks at the local station.
For
each
PVC
supported
in
the
local
line network, there is one output
format NIT entry.
At each station that uses the the NIT formats,
there is one input format NIT entry for each task that
uses
the
communications services.
TXS secondary stations also use the NIT input and output
The
requirements
for,
and
format
of,
NIT
entries
secondaries is essentially the same as at
the
primary
For
those
stations
that
do not support multi-tasking
TM990 and PMSSO) no NIT is required.
formats.
at
the
station.
(such as
The NETGEN program that builds the NIT tables executes
a
series
of
prompts
to
an
interactive
device.
This program uses the
responses to these prompts to
build
the
NIT
entries
for
the
primary
station or the TXS secondary stations.
The user of this
program must know the local line network configuration
in
order
to
properly build the tables.
This program is further described
in Section
3.3.
The concept of 16-bit destination and source IDs is derived
from
the
need
to
extend the range of data link addresses (currently
limited
to
64 for LLM type devices).
These IDs are also used
to
address logical entities (tasks or programs) within a distributed
computer system.
For each physical address (such as LLM or PMSSO
switchs)
and
for
each
task
ID
in a TXS secondary station, a
unique network address is assigned.
This address has
a
decimal
range
of
0
through
9,999,
providing
up to 10,000 unique IDs
within a
network.
Use
of
these
IDs
allows
duplication
of
physical
addresses
(such
as
LLM switch addresses) and logical
addresses (such as task IDs)
within
the
network.
One
ID
is
assigned
to
one
device or one task, and there are no duplicate
IDs within the network.
2270S26-9701
0-13
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