User`s manual
CHAPTER 1
INTRODUCTION AND GENERAL DESCRIPTION
1.1
PURPOSE
AND
SCOPE
This manual
is
intended
to
provide operational pro-
gramming information for
the
DVll
Commu-
nications Multiplexer.
The
manual consists
of
three
chapters plus appendices:
Chapter I provides an introduction and overall
functional and physical descriptions
of
the
DVII;
Chapter 2 contains site preparation, interfacing,
and
installation information;
Chapter 3 includes all information necessary for
operation
of
the
DV
II
via
the
PD
P-II
program;
Appendices contain reference data, commu-
nications introductory data,
and
an extensive
glossary
of
terms
and
abbreviations.
The
reader unfamiliar with communication line pro-
tocols should read Appendix B before attempting
Chapters I and
3.
Terms unique to the
DVII
are generally defined
at
their first appearance. However, should the reader
encounter a word
that
is
not
fully understood, refer
to the glossary provided in Appendix C before
proceeding.
1.2
DVII
COMMUNICATIONS
MULTIPLEXER
The DV II
is
a communications multiplexer for
the
PDP-II
family
of
computers.
By
means
of
the
DVII,
I-I
8
or
16
serial data lines can be multiplexed directly to
PDP-II
core memory for bidirectional data transfer.
The
DVII
is
intended for use with a PDP-II-program
that provides the rules
or
protocol which govern the
data transfers
and
the generation
and
interpretation
of
data link control
and
character codes.
Protocols require processing to
(1) monitor trans-
mitted and received characters in order to identify
and respond to control characters, (2) maintain a
record
of
control and data transmission a nd recep-
tion sequences, and (3) compute the error checking
~ode
(block check calculation) on each character
transmitted
or
received.
The
DVII
performs these
functions, thus relieving
the
processor
of
this over-
head. A Core Memory
Control
Table, set up by
the
PDP-II
program,
is
used by the
DVII
to direct the
processing
of
received
and
transmitted characters.
The control table
is
comprised
of
control bytes,
which form a one-to-one correspondence with each
cha~acter
transmitted
or
received.
1.2.1 D
VII
Ol'eniew Block Diagram
Figure I-I
is
a
DV
II
overview block diagram, show-
ing the principal functional units,
and
data
and con-
trol lines for the DV
II.
The
DVII
consists
of
two
primary functional subsystems, as indicated on the
block diagram: a Modem Control
Unit,
and
a Data
Handling Section. The Modem Control
Unit mon-
itors
and
controls operations
of
the line modems as
directed
by
the PD
P-II
program. The
Data
Handling
Section sequences
and
synchronizes transfer
of
data
between the modems and the
PDP-II
Unibus (effec-
tively, core memory).