MC14526B
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9
APPLICATIONS INFORMATION
Divide–By–N, Single Stage
Figure 11 shows a single stage divide–by–N application.
To initialize counting a number, N is set on the parallel
inputs (P0, P1, P2, and P3) and reset is taken high
asynchronously. A zero is forced into the master and slave
of each bit and, at the same time, the “0” output goes high.
Because Preset Enable is tied to the “0” output, preset is
enabled. Reset must be released while the Clock is high so
the slaves of each bit may receive N before the Clock goes
low. When the Clock goes low and Reset is low, the “0”
output goes low (if P0 through P3 are unequal to zero).
The counter downcounts with each rising edge of the
Clock. When the counter reaches the zero state, an output
pulse occurs on “0” which presets N. The propagation delays
from the Clock’s rising and falling edges to the “0” output’s
rising and falling edges are about equal, making the “0”
output pulse approximately equal to that of the Clock pulse.
The Inhibit pin may be used to stop pulse counting. When
this pin is taken high, decrementing is inhibited.
Cascaded, Presettable Divide–By–N
Figure 12 shows a three stage cascade application. Taking
Reset high loads N. Only the first stage’s Reset pin (least
significant counter) must be taken high to cause the preset
for all stages, but all pins could be tied together, as shown.
When the first stage’s Reset pin goes high, the “0” output
is latched in a high state. Reset must be released while Clock
is high and time allowed for Preset Enable to load N into all
stages before Clock goes low.
When Preset Enable is high and Clock is low, time must
be allowed for the zero digits to propagate a Cascade
Feedback to the first non–zero stage. Worst case is from the
most significant bit (M.S.B.) to the L.S.B., when the L.S.B.
is equal to one (i.e. N = 1).
After N is loaded, each stage counts down to zero with
each rising edge of Clock. When any stage reaches zero and
the leading stages (more significant bits) are zero, the “0”
output goes high and feeds back to the preceding stage.
When all stages are zero, the Preset Enable automatically
loads N while the Clock is high and the cycle is renewed.
Figure 11.
÷
N Counter
P0
P1
P2
P3
CF
RESET
INHIBIT
CLOCK
PE
Q0
Q1
Q2
Q3
“0”
N
V
DD
V
SS
f
in
BUFFER
f
in
N
Figure 12. 3 Stages Cascaded
N0N1N2 N3
N4N5N6 N7
P0P1 P2P3
CLOCK
Q0Q1Q2Q3
f
in
INHIBIT
RESET
V
SS
V
DD
LOAD
N
V
SS
“0”
PE
CF
10 K
V
SS
P0P1 P2P3
CLOCK
Q0Q1Q2Q3
INHIBIT
RESET
“0”
PE
CF
CLOCK
INHIBIT
RESET
“0”
PE
CF
P0P1 P2P3
Q0Q1Q2Q3
N8N9N10N11
V
SS
V
DD
BUFFER
LSB
MSB
f
in
N