1. Unit 11 Latches and Flip-Flops Ku-Yaw Chang canseco@mail.dyu.edu.tw Assistant Professor, Department of Computer Science and Information Engineering Da-Yeh University

2. 22004/04/29Latches and Flip-flops Outline 11.1Introduction 11.2Set-Reset Latch 11.3Gated D Latch 11.4Edge-Triggered D Flip-Flop 11.5S-R Flip-Flop 11.6J-K Flip-Flop 11.7T Flip-Flop 11.8Flip-Flops with Additional Inputs 11.9Summary

3. 32004/04/29Latches and Flip-flops S-R Flip-Flop Similar to S-R latch S = 1 sets the Q output to 1 S = 1 sets the Q output to 1 R = 1 resets the Q output to 0 R = 1 resets the Q output to 0 Essential difference Flip-flop has a clock input Flip-flop has a clock input Q changes only after an active clock edge Q changes only after an active clock edge

4. 42004/04/29Latches and Flip-flops S-R Flip-Flop Operation Summary S = R = 0 no state change S = R = 0 no state change S = 1, R = 0 set Q to 1 (after active Ck edge) S = 1, R = 0 set Q to 1 (after active Ck edge) S = 0, R = 1 reset Q to 0 (after active Ck edge) S = 0, R = 1 reset Q to 0 (after active Ck edge) S = R = 1 not allowed S = R = 1 not allowed

5. 52004/04/29Latches and Flip-flops S-R Flip-Flop Implementation and Timing

6. 62004/04/29Latches and Flip-flops Outline 11.1Introduction 11.2Set-Reset Latch 11.3Gated D Latch 11.4Edge-Triggered D Flip-Flop 11.5S-R Flip-Flop 11.6J-K Flip-Flop 11.7T Flip-Flop 11.8Flip-Flops with Additional Inputs 11.9Summary

7. 72004/04/29Latches and Flip-flops J-K Flip-Flop An extended version of the S-R flip-flop Three inputs J, K, and the clock (CK) J, K, and the clock (CK) J corresponds to S and K corresponds to R J = 1 and K = 0, the output is set to Q = 1 J = 1 and K = 0, the output is set to Q = 1 K = 1 and J = 0, the output is reset to Q = 0 K = 1 and J = 0, the output is reset to Q = 0Difference J = K = 1, the output Q change from 0 to 1, or from 1 to 0 J = K = 1, the output Q change from 0 to 1, or from 1 to 0

8. 82004/04/29Latches and Flip-flops J-K Flip-Flop JKQ Q+Q+Q+Q+0000 0011 0100 0110 1001 1011 1101 1110 Q + = JQ’+K’Q

9. 92004/04/29Latches and Flip-flops J-K Flip-Flop

10. 102004/04/29Latches and Flip-flops J-K Flip-Flop

11. 112004/04/29Latches and Flip-flops Outline 11.1Introduction 11.2Set-Reset Latch 11.3Gated D Latch 11.4Edge-Triggered D Flip-Flop 11.5S-R Flip-Flop 11.6J-K Flip-Flop 11.7T Flip-Flop 11.8Flip-Flops with Additional Inputs 11.9Summary

12. 122004/04/29Latches and Flip-flops T Flip-Flop Also called the toggle flip-flop Frequently used in building counters Frequently used in building counters A T-input and a clock input T = 1 Change the state after the active edge of the clock Change the state after the active edge of the clock T = 0 No state change occurs No state change occurs

13. 132004/04/29Latches and Flip-flops T Flip-Flop Next-state table Characteristic equation Q + = T’Q + TQ’ = T  Q TQ Q+Q+Q+Q+ 000 011 101 110

14. 142004/04/29Latches and Flip-flops T Flip-Flop

15. 152004/04/29Latches and Flip-flops Implementation of T Flip-Flops