lecture18 - CMPT 150 Sequential Circuits Page 5...

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CMPT 150 Sequential Circuits Page 1 Variations on the SR FF b Problem: it is difficult to control signal propagation delays in our circuit. b Solution: Add a clock so that transitions occur on Q a clock pulse. b Problem: When C=1, we still can’t control the signal propagation delays. Q’ CMPT 150 Sequential Circuits Page 2 Master-Slave FF S R Q S R Q S R Q C b This solves the propagation delay problem CMPT 150 Sequential Circuits Page 3 b In order to get rid of the S=1, R=1 state in the SR FF, we can do the following: b The Data or D flip-flop: D Q(t+1) 0 b The Toggle or T flip-flop: S R Q C D Q C 1 D Q C T Q C T Q(t+1) 0 1 CMPT 150 Sequential Circuits Page 4 The JK Flip-Flop b By far the most common type of flip-flop is the JK flip-flop: J K Q C S R Q C Characteristic table J K Q(t+1) 0 0 0 1 1 0 1 1 b JK FF is basically like the SR FF, but with the 11 state doing something useful
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Unformatted text preview: CMPT 150 Sequential Circuits Page 5 Edge-triggered Flip-Flops b The most common way to build a synchronized FF is to have an edge-triggered FF. b Flip-flop latches on rising (falling) edge of clock b Rising edge is called positive, falling edge is called negative b FF holds value until clock starts next rise (or fall for negative) b Timing diagrams: CMPT 150 Sequential Circuits Page 6 Flip-flop Excitation Table b An Excitation table tells you what input you need to supply for a desired transition from state to state b Useful when designing circuits using flip-flops b E.g. the excitation tables for the flip-flops weve seen: Q(t) Q(t+1) D 0 0 1 1 1 1 Q(t) Q(t+1) S R 0 0 1 1 1 1 Q(t) Q(t+1) T 0 0 1 1 1 1 Q(t) Q(t+1) J K 0 0 1 1 1 1...
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lecture18 - CMPT 150 Sequential Circuits Page 5...

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