User`s manual
MODEM CONTROL
INTERRUPT
SET-UP
MODEM
CONTROL
UNIT
MODEMS
I
DATA LINES
TO
---------------~-----
REMOTE
MODEMS
VI
::l
CD
DATA
HANDLING
Z ...------4
::l
SYNC
6FLAGS
Q.
MICRO-
RECEIVED
o
...------f
~------
..
CHARACTER
Q.
PROCESSOR SILO
......
----t
8
~-------"1
RECEIVER
INTERRUPT
CHARACTER
REGISTER
~--------~8~---------------------------------'
~--------~
8 t---------------------------------------------
11-
Z896
Figure I-I
DVII
Overview Block Diagram
1.2.1.1 Establishing the Data Link -
Data
transfer
is
enabled whenever
l.
An
operator
manually initiates a call
to
a
remote modem,
or
the
PDP-ll
program
dials the remote number via the
DNll
Automatic Calling Unit; when the data
link
is
established by the remote modem
answering the call, the
DVII
Modem
Control
U nit signals the
PDP-II
program
via
an
interrupt.
2.
In response to a
RING
signal from a
remote modem, the
DVII
Modem Con-
trol Unit interrupts the
PDP-II
program,
to
initiate an exchange
of
signals
that
establishes the
data
link.
1.2.1.2
DVII
Operation - With
the
data
link estab-
lished, the
PDP-II
program sets
up
the
DVII
Data
1-2
Handling Section to enable the
data
transfer between
the selected local modem
and
core memory.
The
serial/parallel interface
is
accomplished in the
receivers and transmitters. The receivers assemble
characters received from the serial data lines
and
set a
flag each time a character
is
assembled. The trans-
mitters disassemble parallel characters for transmis-
sion on the serial
data
lines
and
set a flag each time
another character can
be
accepted for transmission.
The M aster Scanner cyclically enables the receivers
and
transmitters
to
route
their
flags
to
the
Microprocessor.
The
Microprocessor
is
controlled by a Read-Only
Memory
(ROM), which handles character transfers
and steps the Master Scanner.
Once started by the
PDP-II
program,
the
Microprocessor
runs
continuously.