Flip-Flop Applications

1. Flip-Flop Applications Registers

2. Registers • a register is a collection of flip-flops • basic function is to hold information • a shift register is a register that moves information on the clock signal • serial-in/serial-out • serial-in/parallel-out • parallel-in/serial-out • parallel-in/parallel-out

3. Serial-in, serial-out unidirectional shift register. Figure 6.26

4. Serial-in, parallel-out unidirectional shift register. Figure 6.27

5. Parallel-in unidirectional shift register. Figure 6.28

6. Universal shift register. (a) Logic diagram. (b) Mode control. (c) Symbol. Figure 6.29

7. Flip-Flop Applications Counters

8. Counters Also called pattern generators Function: produce a specified output pattern sequence Types of counters • Binary ripple counters (asynchronous counters) • Synchronous counters

9. State diagram of a counter. Figure 6.30

10. Binary Ripple Counters • also called asynchronous binary counters • the LSB flip-flop recieves clock input from a clock source • the ithflip-flop recieves clock input from output of the ith-1 flip-flop

11. Four-bit binary ripple counter. (a) Logic diagram. (b) Timing diagram. (c) Counting sequence. Figure 6.31

12. Synchronous Binary Counters • Solve the settling time problem of the ripple counters • Every flip-flop changes on clock input simultaneously • Large number of flip-flops can cause loading complications

13. Four-bit synchronous binary counter. Figure 6.32

14. Four-bit synchronous binary counter variation. Figure 6.33

15. Four-bit synchronous binary counter with parallel load inputs. (a) Logic diagram. (b) Symbol. Figure 6.34

16. Synchronous mod-10 counter. (a) Connections. (b) Counting sequence. Figure 6.35

17. 8-bit synchronous binary counter constructed from two 4-bit synchronous binary counters. Figure 6.36

18. Counters Based on Shift Registers • Nonbinary counters • a ring counter: a circular shift register where only one flip-flop is in 1-state and the rest are in 0-state • a switch-tail counter (twisted-ring counter or Johnson counter): complement of the rightmost flip-flop becomes input of the leftmost flip-flop

19. Mod-4 ring counter. (a) Logic diagram. (b) Counting sequence. Figure 6.37

20. Mod-8 twisted-ring counter. (a) Logic diagram. (b) Counting sequence. Figure 6.38

21. Mod-7 twisted-ring counter. (a) Logic diagram. (b) Counting sequence. Figure 6.39

22. Synchronous Counter Design To design a synchronous counter, perform the following steps • Decide the counting sequence • Draw an excitation table, which consists of 3 parts Present state| Next state| flip-flop inputs (flip-flop inputs can be obtained from an application table of the selected flip-flop) • Determine inputs of each flip-flop

23. General structure of a synchronous mod-6 counter using positive-edge-triggered JK flip-flops. Figure 6.40

24. Determination of the minimal-sum expressions for a synchronous mod-6 counter using clocked JK flip-flops. Figure 6.41

25. Logic diagram of a synchronous mod-6 counter. Figure 6.42

26. Determination of the minimal-sum expressions for a synchronous mod-6 counter using clocked D flip-flops. Figure 6.43

27. Determination of the minimal-sum expressions for a synchronous mod-6 counter using clocked T flip-flops. Figure 6.44

28. Determination of the minimal-sum expressions for a synchronous mod-6 counter using clocked SR flip-flops. Figure 6.45

29. Complete state diagram for the synchronous mod-6 counter of Fig. 6.42. Figure 6.46