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Principles of Operation
3-5. Direct Memory Access (DMA)
The INP uses an LSI OMA-controller chip
to
provide
three
high
speed
channels
between data buffers in RAM and the HP-IB Inter-
face, as well as between RAM and datacomm LSI devices.
The
fun-
ction
of the DMA logic is to move bytes between external devices
and RAM in such a way that they will be transparent
to
the
INP
Microprocessor
software.
This
ability
to transfer data con-
currently with instruction execution enables the INP
to
achieve
high throughput rates.
3-6. SDLC and BISYNC Data Communication
The INP uses LSI datacomm devices that are programmed by the
INP
Microprocessor
to
operate with BISYNC and SDLC protocols.
When
transmitting, these devices receive data
and
control
bytes
in
parallel
from
the
INP
Microprocessor
and convert them into a
continuous serial stream for transmission.
Simultaneously,
they
can
receive
a serial stream of data and control information and
assemble it into a series of parallel
data
bytes
for
the
INP
Microprocessor.
3-7. Communication Line Interfaces
The communication line interfaces,
Direct-connect,
etc.,
translate
signals that are electrically and
the respective standards.
3-8.
AUTO CALL UNIT INTERFACE
such
as
RS232C,
Bell
DDS,
data
and
control
lines into
mechanically
compatible
with
The ACU interface uses a single cable which combines the
RS
232
and
RS
366
standards.
Therefore, the INP can be connected to
both the modem and the ACU without using
two
cables.
The
ACU
interface
will
allow
automatic
dial-up of phone lines through
programmatic or command accesses.
HP supports the Bell 801C Auto
Call Unit (used with Bell modems), and the Racal Vadic VA811 Auto
Call Unit (used with the HP 37210T modem).
3-9. FUNCTIONAL-LEVEL OPERATION
In the following typical message transmission sequence,
a
modem
telephone
line
is assumed as the communications medium.
Refer-
ences are made to the functional areas, data paths,
and
service
request
paths
within
the
block
diagram
in
figure
3-1.
The data paths and service request paths
being
referenced
are identified in the diagram by circled numbers.
3-4
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Table of Contents
Troubleshooting
