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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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