Model 34SSA
THEORY OF OPERATION
Section
Vlll
of US8 high to latch the switch code
and
also sets the inter-
rupt input
to the main processor.
8-171
. Upon recognizing the
interrupt input, the processor
sets the interrupt
enable output high to enable buffers U59
and U60
and reads the switch code. This code
represents
a
vector address
to
the processor. The
processor performs
the
program
routine contained at the address
indicated which
includes transferring the
new switch data to the inguard
controller
and outputting data to the front panel to change
the necessary
cnunciators.
8-172. The new enunciator data is output to the data bus
(lines D0
through D7)
by
the main processor and applied to
the inputs of
latches U6S through U70. The new enunciator
code is contained on lines
00
through 05. Lines
06 and
07
are applied to the select
inputs
of
decoder U64 and arc used
to
determine which output of U64 will be set low. Outputs
1Y0 through
1Y3 are enabled
by
the signal from device
select
decoder U41. Outputs 2Y0 and 2Y1 are enabled by
8-173.
Display. Measurement
data
is transferred
to the
display one number
at a
time. The polarity
or
numerical
data is applied to the input of latch US4 and the digit (or
position in the display) and decimal information is applied
to
the
input of latch U63. The output of device select
decoder U41 is applied to the clock input of US4 and U63
to latch the
information. The position
information is ap-
device select decoder
U33. The outputs of U64 are acti-
vated
by the delayed clock signal from
U52F and applied
to the clock inputs of latches
U6S
through
U70. All
outputs of U64 are high except the one driving
the latch
which is to accept the
data.
The
enunciators are lit when
the output of the latch driving them is set
low.
plied to the select and
data inputs of US6 to determine
the
proper display driver to be activated.
The outputs of U.56
are applied to the display drivers
(Q1
1 throu^
Q18)
and
are enabled by- the signal from
U48B (interrupt circuitry).
The display is
scanned
from left to right one
number at a
time.
8-33/8-34
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