User`s manual
This chapter provides information for interfacing,
installing, and testing the
DVII
Communications
Multiplexer. Interfacing considerations are discussed
in Section 2.1, Site Preparation and Planning.
Instal-
lation, customizing,
and
checkout procedures are dis-
cussed in Sections
2.2
through 2.7.
2.1
SITE
PREPARATION AND PLANNING
2.1.1 Minimum
Through Maximum Configurations
The
DVII
provides multiplexing capability to PDP-
i I core memory for up to
16
modems.
The
DVII
is
housed
in
a nine-slot, double system unit and includ-
es one rack-mounted distribution panel for each
group
of
eight modems in a system. Five
of
the nine
slots are occupied by functions required in any
sys-
tem configuration. The remaining four slots are occu-
pied by four hex-printed circuit boards (M7839
or
M7833), designated as the line cards. Each line card
is
capable
of
supporting
data
transfers to and from four
modems.
The
M7839 line card supports synchronous
data
transfers while the M7833 supports asynchro-
nous data transfers (these line cards contain the
receivers
and
transmitters).
The 5-module unit common to all DV
11
con-
figurations
is
designated the
DVII-AA.
Two
of
the
M7839 module, plus one distribution panel and
asso-
ciated cables, form an eight line synchronous unit
designated the DVII-BA. An eight line asynchronous
unit, the
DVll-BB,
is
generated by replacing the
M7839 modules in the
DVII-BA
unit with two
M7833 modules. Similarly, a mixture
of
one
of
each
line card forms a synchronous/asynchronous unit
designated the DVII-BC. The minimum
DVll
sys-
tem configuration consists
of
one
DVII-AA
unit plus
one line card option,
DVII-BA,
DVII-BB
or
DVll-
BC;
a maximum configuration consists
of
one
DVll-
AA
unit plus two line card options.
2-1
CHAPTER 2
INSTALLATION
2.1.2 Compatibility Considerations and Precautions
The
DVII
with synchronous line cards
is
directly
compatible with
Bell
synchronous modems 201, 208,
209,
or
equivalent.
It
is
also compatible with Bell
asynchronous modems
202 series,
103
series
or
equiv-
alent when asynchronous line cards are used. The
DVII
provides internaal clock rates
of
1200,
2400,
4800, and 9600 baud at
0.005% accuracy for synchro-
nous operation; modems operating at other rates
must supply their own clock signals.
It
is
recommend-
ed that modem-supplied clocking be used where
available.
The
DVII
is
compatible with all members
of
the
PD
P-II
family
of
computers.
PDP-II
standard soft-
ware address allocations provide for the implementa-
tion
of
as many as four
DVlls
in a
PDP-II
system.
DVII
throughput rate, however, forms a more severe
limitation on the number
of
DVlls
in a system, as
will now be demonstrated.
A single
DVII
mUltiplexing
16
modems
at
9600
baud, each
in
full duplex mode,
is
capable
of
transfer-
ring 38,400 8-bit characters per second (1200 charac-
ters per line X
16
lines X 2 directions). Although this
is
well
within the capabilities
of
the
DVll,
on the
average, the
PDP-ll
is
provided with only
26
IlS
to
handle each character. Although most characters are
handled by
NPR
transfers, program and protocol
efficiencies still need to
be
relatively high to maintain
this rate; this would
be
for a single
DVII.
Some
76,800
NPR
cis
would be required,
or
about
10
per-
cent
of
Unibus capacity. With all lines operated in
DDCMP
mode (control byte fetch inhibited), 38,400
NPR
cis
would be required,
or
about 5 percent
of
Unibus capacity.