Racal Instruments 9916 Workshop Manual page 31

I
I
I
I
I
_ _J
SEVEN
SEGMENr
DECODER
' - v - - - - '
1 SEGMENTS
t-
d,p
I
I
L _
1 - - - - - - - - - - - - -
1
I
By
I
}""+- -t t -
j- -j-
-r--{--r- i
~::+~"
I I ,
I
,1, ,1, , , ,
I I , , ,
OICITAL
I "
I , , , , I I , , J I I I
I
INDICATORS
I
I
I
SEGMENT CHECK
--------:~-__I
INDICATOR Bl.ANKING
----'--_.,;;>--_ _
--1
8CO
TO
DECIMAL
Of
co
DE
RESET
RIo!
8CO
COUNTER
SERIAL RtAoour}
:.~:~=== ~~
J
OAr... fROIrol T
COl CHt"
,.
Multiplex Display System
Fig.3.2
Multiplex Readout
3.4 The readout data is fed from the CD! Chip to the Display Assembly via a
four-line b.c.d. connection. To permit this simple interconnection a
parallel-ta-serial (multiplex) system is used. The principles are shown in Figure 3.2,
al though it should be noted that part of the system is in the CDI Chip.
3.5 In the CDI Chip the data stores feed in parallel into a common b.c.d. four-
Iine output. The store outputs are enabled in turn for approximately 100
micro-seconds by ala kHz reference signal, derived from the frequency standard.
3.6 The b.c.d. data is fed to a 7-segment
de~oder
(ICl) in the Display Assembly,
which offers the decoded data to the bank of I.e.d. numerical indicators. The
la kHz reference signal is fed to a counter and BCD/Decimal decoder, enabling each
indicator in turn for 100 microseconds: A reset pulse R(o) which is generated in the 100
state of the counter ensures that the display enable is synchronised with the data store
I .
readout. Provision is made via ICl for a segment check and also for blanking out the
display in BURST mode.
3-3