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MC14522BCL Datasheet(PDF) 8 Page - Motorola, Inc |
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MC14522BCL Datasheet(HTML) 8 Page - Motorola, Inc |
8 / 10 page MOTOROLA CMOS LOGIC DATA MC14522B MC14526B 8 APPLICATIONS INFORMATION 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. 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. Figure 11. ÷ N Counter P0 P1 P2 P3 CF RESET INHIBIT CLOCK PE Q0 Q1 Q2 Q3 “0” N VDD VSS fin BUFFER fin N Figure 12. 3 Stages Cascaded N0 N1 N2 N3 N4 N5 N6 N7 P0 P1 P2 P3 Q0 Q1 Q2 Q3 fin CLOCK INHIBIT VSS VDD LOAD N VSS RESET “0” PE CF 10 K Ω VSS P0 P1 P2 P3 Q0 Q1 Q2 Q3 CLOCK INHIBIT RESET “0” PE CF CLOCK INHIBIT RESET “0” PE CF P0 P1 P2 P3 Q0 Q1 Q2 Q3 N8 N9 N10 N11 VSS VDD BUFFER LSB MSB fin N |
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