System-Level Operation - HP 3000 Series Installation And Service Manual

Principles of Operation
LSI devices, ( 10) The datacomm device that is being used
ser ial izes the data and sends it over the 1 ine, (11)
effectively completing the initialization of data transmission.
The INP initiates the data reception function by initializing the
modem control lines to indicate that data can be received. It
then begins monitoring the communication line for a start-of-
message sequence.
Having initialized the transmission and reception of data, the
INP Microprocessor now performs functions such as managing
special characte rs in the data stream, calculating and compar ing
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.
4-9. SYSTEM-LEVEL OPERATION
The following discussion demonstrates the functioning of an INP
at the system level. A very basic DS/3000 example is given here,
but INP usage with other data communications subsystems (such as
RJE, MRJE, etc.) can easily be construed.
INP ope ra tion begins with the sys tem opera tor opening the DSLINE
(by means of the =DSLINE 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 INP
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 tha t messages com ing fr om 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 INP then becomes dormant until the next
=DSLINE command.
4-5