Ch. 12 : Counter Circuits

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Ch. 12 : Counter Circuits

& Applications

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Outline Outline

Analysis of Sequential Circuits Ripple counters

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Design of Divide-by-N Counters Ripple Counter ICs

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System Design Applications

7-Segment LED Display Decoders

S h C t

Synchronous Counters

Synchronous Up/Down-Counters ICs

A li ti f S h C t IC

Ch. 12: Counter Circuits 2

Applications of Synchronous Counters ICs

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12.1 Analysis of Sequential y q Circuits

p

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12 2 Ripple counters 12.2 Ripple counters

A counter circuit can be built by cascading flip-flops together.

(Connecting the Q output of one flip flop to the clock input of the (Connecting the Q output of one flip-flop to the clock input of the next)

The number of states in a counter (modulus) is 2^N where N is the number of flip-flops.

number of flip flops.

In order for a counter to operate properly each flip-flop must toggle. For J-K flip-flops this means both J and K must be high.

In a ripple counter the clock input has to propagate through each pp p p p g g flip-flop of the counter.

A ripple counter is also called an asynchronous counter because each flip-flop does not change at the same time.

The propagation delay of each flip-flop adds together to give a

total propagation delay for the counter. This propagation delay will limit the maximum frequency allowed by the input trigger clock.

A down counter can be formed by taking the output from the

A down counter can be formed by taking the output from the output instead of the Q output of each flip-flop.

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Three bit binary ripple counter Three bit binary ripple counter

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Effect of propagation Delay Effect of propagation Delay

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Down Counter (Exp: Mod 8) Down Counter (Exp: Mod 8)

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12.3 Design of Divide-by-N g y Counters

A counter can also be used as a frequency divider. q y

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Mod 6 : 7 6 5 4 3 2 7 6 5

Mod 6 : 7,6,5,4,3,2,7,6,5,…

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Count 0,1,2,3,4,5 and then , , , , , stops and turns on an LED

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12 4 Ripple Counter ICs 12.4 Ripple Counter ICs

7490 (mod 2 x 5) 7492 (mod 2 x 6) 7492 (mod 2 x 6) 7493 (mod 2 x 8)

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7493 7493

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7490 7490

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7492 7492

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12 5 System Design Applications 12.5 System Design Applications

Digital Clock Timer Up

Timer Up

Timer Down

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Di it l Cl k Digital Clock

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Timer up till 3 minute Timer up till 3 minute

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12.6 7-Segment LED Display g p y Decoders

p

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12 7 Synchronous Counters 12.7 Synchronous Counters

p

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12.8 Synchronous Up/Down- y p Counters ICs

p

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12.9 Applications of pp

Synchronous Counters ICs

p

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Kuis Kuis

Count up 34563456, 4567845678

Count down 65436543: 8765487654 Count down 65436543: 8765487654 Timer up 012345 : 012345678

Ti d 543210 876543210 Timer down 543210: 876543210

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Ch. 12 : Counter Circuits