The Cdi Chip - Racal Instruments 9916 Workshop Manual

THE CDI CHIP
3.1 A basic digital frequency meter comprises a chain of de<;:ade counters feeding
b.c.d. data into latched stores. Counting is controlled via a main gate which
is opened for a period determined by the time base. Provision is made for resetting the
counter and releasing the data for display. In the 9916 these functions are carried out in
the integra'ted circuit lC4, which achieves large scale integration, using the col lector-
diffusion-isolation principle. For convenience, IC4 will often be referred to in the
handbook as the 'CDI Chip'. Fig 3.1 is a simplified diagram of the frequency measurement
mode, showing the principal functions performed by the CDI Chip.
c:;=
'SPLAY
MULTIPlEXED BeD
OUTPUT DATA
I
STORES
I
I
I~PUT
INPUT
(JATE
1
CIRCUITS
COUNf(R
I
CONTROL
I
I I
FREOUENCY
I
I
CD I
TlHE 8ASE
'So
TANOARQ
I
CHIP
Ext£RNAl
t;
1
STANDARQ
, Y
,
.
). LINE TIME BASE SELECTiON
·9916 Vol. 2
Basic FrequencY
~eter
Fig. 3.1
3-1