Texas Instruments 990 User Manual page 220
Dx10 hdlc communications package
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- Operation manual (276 pages) ,
- Manual (211 pages) ,
- Installation and operation manual (122 pages)
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Throughput
B.5
FCCC MULTILINE OPERATION
The communications package software
supports
operation
of
all
four
channels,
or
lines, of the FCCC card included in the DXlO
system.
Including the FCCC card in DXIO is a
system
generation
function
and
including
the HDLC operation of an FCCC line is a
network generation function.
Any FCCC line to be operated by the
HDLC package is .specified at network generation time.
A
set
of
software
programs
off loaded in FCCC RAM at COMMGO time performs
the
HDLC
data
link
control,
polling,
and
timing
functions
required
to
control traffic flow at the data link level.
After
the
user
specifies
the
number
of
FCCC
lines
and
the
characteristics
of
these
lines
during network generation, the
tables are created to operate the FCCC lines as specified.
This
operation is transparent to the user tasks.
B.5.l
Data Rate Selection for Multiline Operation
The
FCCC
card has a total character-handling capability of 3800
characters per second (cps), one character equals
one
eight-bit
byte.
This
limits
FCCC
throughput to an average of less than
9600 bits per second (bps) per channel.
In the synchronous mode,
a 9600-bps (9.6K-bps) line can transfer 1200 cps.
Therefore, the
FCCC
cannot
operate
at
9.6K
bps
on
all
four
channels
simultaneously.
A
lesser
aggregate bandwidth must be selected
for the FCCC to operate correctly.
Refer to Section 3
for
data
rate
combinations
that
can be selected to make use of the FCCC
maximum
bandwidth.
This
chart
should
be
consulted
before
beginning
the
network
generation
process
and
when
creating
documentation on the network.
B.6
AVOIDING BOTTLENECKS
Depicted below is a communications system node
with
a
9600-bps
communications
line
and
a
300-bps
print
device.
Messages
arriving at this node are directed to the print device.
A
rapid
succession
of input messages arriving on the communications line
at 1200 cps is printed out at
37.5
cps.
Under
any
practical
conditions,
the
communications
buffers
available
to
that
secondary station soon fill
up
and
the
communications
system
stops
accepting
input
messages from that station (that is, the
node rapidly becomes congested, at
least
for
that
station
or
line,
because
the communications transfer rate is significantly
higher than the printer transfer rate).
B-8
2270526-9701
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