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Principles of Operation
Initially, the HP 3000 is powered up, and the communication
line
has been installed, but is not currently operational. The process
of powering up invokes the
ROM-resident
control
program.
The
control
program both resets the !NP logic and verifies !NP oper-
ation.
The results of the operation verification
are
available
to the HP 3000 on request.
To initiate transmission, the system issues a
control
parameter
over
the
Hewlett-Packard
Interface
Bus
(HP-IB)
to the HP-IB
Interface of the INP,
(1) •
This action causes an interrupt bit
to be set,
(2) , which interrupts the INP Microprocessor,
(3) •
The INP Microprocessor then reads the interrupt register,
(4)
,
to
determine
which device is requesting service.
Next, the INP
Microprocessor
interrogates
the
HP-IB
Interface,
(5)
,
to
determine
the nature of the service being requested (new control
word, new data word, etc.).
In this example, the control word read in
(5)
tells
the
INP
microprocessor
to
start
transferring data words from the HP-IB
Interface to the !NP RAM for local buffering.
Typically, the !NP
reads a whole buffer or block from the HP 3000
before
beginning
to transfer data over the data communication line.
The following steps occur between the INP and the auto call
unit
in
the
process
of establishing a connection between two remote
points:
The !NP performs a DLO (data line occupied) and then, if the data
line is unoccupied, raises DLO and performs a CALL REQUEST.
The
auto call unit responds with a PND (present next digit).
The !NP
then sends a DIGIT PRESENT along with NBl, NB2, NB3, NB4
(repre-
senting
the phone digits).
After the phone digits are sent, the
auto call unit responds with a DSS (data set status), which indi-
cates that a connection is established.
The flows from the HP 3000 into memory are represented by
(6)
and
(7)
in figure 3-1.
Upon receiving a full
block,
the
!NP
Microprocessor
raises
RTS,
(8) , and sets up an interrupt for
when the modem returns CTS.
When CTS becomes active,
an
inter-
rupt
is
generated
to
the
!NP Microprocessor,
(9) •
The !NP
Microprocessor then sends data from the !NP RAM to
the
datacomm
LSI
devices,
(10)
•
The datacomm device that is being used
serializes
the
data
and
sends
it
over
the
line,
(11)
,
effectively completing the initialization of data transmission.
The !NP 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
3-5
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Troubleshooting
