L-.
3-7. The guarded bus connects the controller to the
analog modules through the Bus Interconnect Board or
through the optional Isolator module; the Isolator must
replace the Interconnect Board if an optional remote inter-
face
is installed. The yarded bus consists
of
the following
lines:
1 . Address/Control (IC) lines
—7.
2.
Bidirectional
data (ID) lines
—8.
3.
Real time lines —9.
4.
Handshake
line (AC'K)
~1
.
5 . Power Supply lines.
3-8.
'
The address, handshake,
and
data
lines
of the two
buses serve the
same functions. The
real time and power
supply lines
may
have
differing functions. For example, the
RT lines in
the unguarded
bus
are unused except
for R.T5
(frequency
reference). The
RT lines in the guarded bus
form an
analog bus which carries
all the conditioned and
converted analog signals between the
analog
modules.
The
external reference input lines
are part of the analog bus
(RT7
and RTS). Logic supply
lines (Vcc and Vss)
will
be
different
in the two busses if
an isolator option is installed,
in the guarded bus, Vcc and Vss are
always
-
1 5V and —20V
with respect to analog common. In the unguarded
bus
with
an
interconnect
pcb
installed
Vcc and Vss are diode coupled
to the
guarded bus. But with the isolator option installed,
Vcc an d Vss are isolated
from analog common
.
3-9.
The high quality bus consists of lines connecting
the input switch (Sense HI and ID, source HI and LO,
Guard, Ohms Guard) to the signal conditioning and con-
verting modules (AC converters. Ohms converter, etc.).
Ohms guard is only available through the rear
inputs.
3-10.
Controller
3-1
] .
Under the direction of the software program, the
controller addresses and sets up each of the modules
neces-
sary
to perform a function. Two types of addresses are
used:
direct
and
indirect. An indirect address requires
a
previous direct address
to set
up the indirect address
response
logic.
Data
transfers are accomplished with a
hand-
shake between the address (IC) lines and the
acknowledge
(ACK) line.
When
the controller
addresses
a module, it
places data on
the
data (ID)
lines or receives
data
from the
addressed module.
The addressed module must
respond
with
an ACK
signal signifying that it is receiving
or
sending
data.
3-12.
Tlie controller directs the R^ A/D converter
in
taking
a
sample
and
receives the sample data from the
converter.
The controller stores range and function infor-
mation for application to the sample data. Using the arith-
metic capability of the microprocessor, the software
pro-
cesses the
data
to arrive at a binary
2’s
complement
number
which represents the polarity and value
of the
measurement.
This number is made available to an optional remote inter-
face either
as is or
after further processing to
ASCII
code.
The
number is
further
processed by the controller for
application to the front pane! display in
a
seven segment
LED
format.
3-2
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