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Divide–By–N, Single Stage
Figure 11 shows a single stage divide–by–N application.
The MC14522B (BCD version) can accept a number greater
than 9 and count down in binary fashion. Hence, the BCD
and binary single stage divide–by–N counters (as shown in
Figure 11) function the same.
To initialize counting a number, N is set on the parallel in-
puts (P0, P1, P2, and P3) and reset is taken high asynchro-
nously. 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. Re-
set 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" out-
put pulse approximately equal to that of the Clock pulse.
LSB
N0 N1 N2 N3
P0 P1 P2 P3
Q0 Q1 Q2 Q3
f in
CLOCK
INHIBIT
V SS
RESET
"0"
PE
V DD
LOAD
N
10 KΩ
V SS
MC14522B MC14526B
6–314
APPLICATIONS INFORMATION
P0
Q0
Q1
P1
N
Q2
P2
Q3
P3
V DD
CF
"0"
RESET
INHIBIT
V SS
f in
CLOCK
PE
Figure 11.
N4 N5 N6 N7
P0 P1 P2 P3
CLOCK
CF
INHIBIT
V SS
RESET
Figure 12. 3 Stages Cascaded
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 sig-
nificant 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 sig-
nificant 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.
BUFFER
f in
N
N Counter
Q0 Q1 Q2 Q3
CF
"0"
PE
V SS
MOTOROLA CMOS LOGIC DATA
MSB
N8 N9 N10 N11
V DD
P0 P1 P2 P3
Q0 Q1 Q2 Q3
CLOCK
CF
INHIBIT
RESET
"0"
PE
BUFFER
f in
N
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