Technics ST-9038 Manual page 8

I
PART
PLL
SY
ESIZER.
When
the input frequency
fin
enters
the down
of
74LS192 the counter countsdown from
9,8,7
...
1
to
0.
When
the
counting proceeds
from
0 to
9, the borrow output
is
delivered. That
is,
the
input
frequency
fin
is
divided at the
r:atio
of
l/10.
The borrow output
is
put into
¡rPD861C where the
frequency is divided as programmed (codes
from
P'l
-
P6) and
finally
negative
pulse
"1"
is
Out
out.
87
LSI6ísinvertedbythispulse.
SupposethatO
="O"andÕ
="1".
Thenthelogical circuitisas
follows:
74L5192
861C
A
c
D.
tl
¡
A B
C. D
E
o
o
"1"
B
74LS76
Counter
for
scan
From the table
of
true
values
for
OR and AND;when,
"1"
and
"0t'
are
respectively
put
in one
side
of
OB and that
of
AND, then the output
is
"1"
for
OR and
"0"
for AND
irrespective of the input
on the other
side. That
is,
the
kind
of
code
put into the
scanning counter
has
nothing to do with
the results in the above
circuit.
.
Therefore, the code
of 741S192
is
[1010] [5] that of
861C is [010111]
_
t58l
.
Next,
as
861C is "
J
",A74L574
transmits
the D input,
therefore O
-
"1"
and
O=
"0".
Atthat
time, when the content
of
74LSl92
becomes
1 (i.e. OA,
OB, OC and OD are respectively
1,0,0,
O.),
"0"
is added
to all
the diode OR circuits and, therefore, the D input
of
874LS74
becomes
"O".
The D input
is
transmitted
to
O
with the next
Iin
"
--f
".
ln
other words,
"0"
is transmitted
to
O and
the
load signal
is
generated. The generation
of
load
signal causes
the
input [1010]
of
Dn
-
Do
to be preset,
therefore the resultat correcting
is
g - 2+
1*Sinsteadof
9- 2*1*0.
Símultaneously,terminal
CLRof
A74LS74
isclearedwith"O"
added,
and corisequently Õ
becomes
"1".
Then,
the D
input
of
874LS74 becomes
"1",
and
O
is
"1"
with the next
fin "
-l
",
causing
the
load signal
to go
out.
ln the above condition, however, 74LSl92 doesn't count and its content
"5"
remains as
it
is.
With the next
fin
"
J
",74LS192performs
counting:
5+4
*3*2
*1
*0
--9
*8
.-.-:--- That
is,
9
- 2*1 -'@*@*@*@*Ø*O*O
+B+B
""""
Thus, the counting include extra six
pulses
as
shown
by encircling the
numbers.
To
summarize
the
above
description, when
¡tLI-"
(this
òan
be considered
asthe
load signal
from
861C) comes
out at the
OUT
of
861C,
it
includes
6
pulses more
than the ordinary
signal.
Accordingly,
the
number
of
frequency divisions
by the fixed
codes
is 586
obtained by adding
6
and 10
x
58 = 580
that
is
the
number
of frequency divisions by 74LS192
and 861C.
"o" o
"1"
-o
3j
CI
o
6