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Principles of Operation
special characters in the data stream, calculating and
comparing
CRCs,
transferring
blocks to and from the HP 3000, and managing
modem signals.
When
an
end-of-message
sequence
is
detected,
the
CRC
is
calculated
and
checked.
If there is no error, the message is
accepted and transferred to the HP 3000.
The INP returns to
its
task
of
monitoring
the
line
for
the
next
start-of-message
sequence.
Terminating
the
transmission
sequence
involves
sending
the
necessary end-of-message information and changing the appropriate
modem control lines to indicate the end of transmission.
3-10. SYSTEM-LEVEL OPERATION
The following discussion demonstrates the functioning of
an
!NP
at the system level.
A very basic DSN/DS example is given here,
but INP usage with other data communications subsystems (such
as
DSN/RJE, DSN/MRJE, etc.) can easily be construed.
INP operation begins with the system operator opening the DS line
(by means of the :DSCONTROL OPEN console command).
At this
time
the INP hardware logic is reset and the ROM-resident verification
test (SELF TEST) is invoked.
Upon the successful
completion
of
SELF
TEST,
the respective communications line protocol software
is downloaded to the INP RAM.
The HP 3000 then commands the
!NP
software to begin execution.
The software initializes itself
to
conform
to
the
DSLINE
as
configured
on
the
mainframe.
At this time, a read command is
issued to the INP,
so
that
messages
coming
from
the
remote
computer
through
the
data communications line can be received.
When a message is received from the remote
computer,
the
local
HP 3000 is notified (and data is moved to the mainframe RAM) only
at successful completion of the read.
Closing the DSLINE causes any current INP - to - HP 3000 messages
to
be
completed.
The
!NP
then
becomes
dormant
until
the
next :DSCONTROL command.
3-6
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Troubleshooting
