Technics ST-9038 Manual page 5

*
t
ESIZER
1-5
Programmablefrequencydivider
The
prograr"nmable
frequency (variable) divider plays the most important role in
setting
the
frequency
for the PLL
synthesizer.
Thefrequencydividingratio 1ln=1/983(9BB)
-
llBOnecessaryfortherespectivecountryisdone
in this section.
ln
the
case
of
this equipment, lC's
SVlSN74LS192 and ¡rPDB61 are
series-con-
nected,
and
the
results
of
division
by
the fixed and
variable codes are totalled
to
achieve the
dividing ratio.
"1"
74L574
ü
o
$
fin
,Ç
.O
-.9
87
(88)
-
107
To
Phase
comparator
Programmable
frequency divider circuit
1-5-1
Operational description
of
lC
SVISN74LS192
4-bit BCD up/down programmable
counter.
ln this
circuit,
it
is used
as a
down counter, and the borrow output
is
fed into
¡rPDB61C.
When
the
BCD
output
changes
from 0 to g,
a
down counter input
pulse
of
negãtive
polarity
äppears
at
the borrow output.
Also, when
the load line
is
ar
"1"
level,
the inputs of
tl-ie preset inputs Da
-
Do
are
inhibited
and
the counter counts down the frequency. But when the
load signal becomes
"0"
level, the preset
data are given
priority
and set ¡nto each
F/F
irrespective of the input frequency conditions.
When
the load line
is
again
shifted
back
Io
"1"
level,
the counter
counts
down from the
preset
value.
c
o
õ
D
ocK
CLR
B
74L574
oA oB oc
oD
74L5192
Load
Db Dc
Dd
down
Ða
Borrow
CLR P2
P3 P4 P5
P6
P7
P8
pPD861C
OUT ln
3