Basic Frequency Meter - Racal Instruments 9901 Maintenance Manual

CHAPTER
3
PRINCIPLES OF
OPERATION
THE CPI CHIP
3.1
A
basic digital
frequency meter comprises a chain
of
decade 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 timebase. Provision
is
made
for
resetting the
counter
and
releasing the
data
for
display.
In
the 9901 these functions are carried
out
in
the integrated
circuit
IC2,
which achieves large scale integration, using the collector-
diffusion-isolation principle. For
convenience, IC2
will often
be
referred to in
the
hand-
book
as
the
'CD
I
Chip'
.
3.2
In
addition to
frequency measurement,
the
CDI Chip performs
numerous
other
functions
such
as
Autorange operation and the correct routeing of signals
for
start/stop,
time base drive and external standard input, etc.
Basic Frequency Meter
Fig.
3.1
9901 Vol.
2
3-1