1. Flip-Flops and Registers
Chapter 10
Flip-Flops and Registers 1

2. Objectives You should be able to:
Explain the internal circuit operation of S-R and gated S-R flip-flops.
Compare the operation of D latches and D flip-flops by using timing diagrams.
Describe the difference between pulse-triggered and edge-triggered flip-flops. 2

3. Objectives (Continued)
Explain the theory of operation of master-slave devices.
Connect IC J-K flip-flops as toggle and D flip-flops.
Use timing diagrams to illustrate the synchronous and asynchronous operation of J-K flip-flops. 3

4. S-R Flip-Flop Data storage circuit Cross-coupled NOR scheme
Asynchronous set and reset 4

5. S-R Flip-Flop
Function table 5

6. S-R Flip-Flop
Data storage circuit
Cross-coupled NAND scheme 6

7. S-R Flip-Flop
Function table 7

8. S-R Flip-Flop Both true and complemented Q outputs
Symbols for a S-R FF 8

9. S-R Flip-Flop Timing Analysis9

10. S-R Flip-Flop Application
Storage register to remember time of day when a temperature limit switch goes high. 11

11. Gated S-R Flip-Flop
Asynchronous – output responds immediately to input
Synchronous – output responds in step with a control input 13

12. Gated S-R Flip-Flop
Function table and symbol 14

13. Gated D Flip-Flop
Data flip-flop with example inputs and outputs 15

14. Discussion Point
How will the complement of an output differ from the output?
Explain the difference between synchronous and asynchronous inputs. 16

15. 7475 Integrated Circuit D Latch
Four transparent D latches
Bistable latch, logic symbol and pin configuration 17

16. 7474 Integrated Circuit D Flip-Flop
Positive edge-triggered device
Transitions of output occur at the edge of input trigger pulse
Clock signal usually used as trigger pulse 19

17. 7474 Integrated Circuit D Flip-Flop
Logic symbol and pin configuration 20

18. Integrated Circuit D Flip-Flop
Positive edge-detection circuit 21

19. Integrated Circuit D Flip-Flop
Synchronous inputs
D (Data)
Cp (Clock)
Asynchronous inputs
SD (Set)
RD (Reset)
Function Table (see Table 10-4 in the text)
Setup Time - time D must be stable before transition of Cp 22

20. Master-Slave J-K Flip-Flop
Toggle mode
Switches to opposite state at active clock edge
Master-slave
Master receives data while input trigger is HIGH
Slave receives data from master and outputs it when clock goes LOW 24

21. Master-Slave J-K Flip-Flop
Function Table 25

22. Master-Slave J-K Flip-Flop
Equivalent circuit and logic symbol 26

23. Master-Slave J-K Flip-Flop
Pulse-triggered (level-triggered)
Input data is read during entire time clock pulse is at a HIGH level
Ones catching 27

24. Edge-Triggered J-K Flip-Flop
Accepts data on the J and K inputs only at the active clock edge
Symbols for positive and negative edge triggered J-K FFs 28

25. Edge-Triggered J-K Flip-Flop
Function Table 29

26. Discussion Point
How are pulse triggered (level triggered) devices different from edge triggered devices?
What is ones catching?
Identify the synchronous and asynchronous inputs on a JK flip-flop logic symbol 30

27. Integrated Circuit J-K Flip-Flop
master-slave
74LS76 - negative edge-triggered
Logic symbol and pin configuration 31

28. Integrated Circuit J-K Flip-Flop
To form a D flip-flop add an inverter 33

29. Integrated Circuit J-K Flip-Flop
To form a toggle flip-flop tie inputs HIGH 34

30. Using an Octal D Flip-Flop in a Microcontroller Application
Octal ICs - eight on a chip
8-bit register
74HCT273 logic diagram 35

31. Using an Octal D Flip-Flop in a Microcontroller Application
The 74HCT273 as an update and hold register
Figure 10-45 36

32. Summary
The S-R flip-flop is a single-bit data storage circuit that can be constructed using basic gates.
Adding gate enable circuitry to the S-R flip-flop makes it synchronous. This means that it will operate only under the control of a clock or enable signal. 37

33. Summary
The D flip-flop operates similar to the S-R, except it has only a single data input, D.
The 7475 is an integrated-circuit D latch. The output (Q) follows D while the enable (E) is HIGH. When E goes LOW, Q remains latched. 38

34. Summary
The 7474 is an integrated-circuit D flip-flop. It has two synchronous inputs, D and Cp, and two asynchronous inputs, SD and RD. Q changes to the level of D at the positive edge of Cp. Q responds immediately to the asynchronous inputs regardless of the synchronous operations. 39

35. Summary
The J-K flip-flop differs from the S-R flip-flop because it can also perform a toggle operation. Toggling means that Q flips to its opposite state.
The master-slave J-K slip-flop consists of two latches: a master that receives data while the clock trigger is HIGH, and a slave that receives data from the master and outputs it to Q when the clock goes LOW. 40

36. Summary
The 74LS76 is an edge-triggered J-K flip-flop IC. It has synchronous and asynchronous inputs. The 7476 is similar, except it is a pulse-triggered master-slave type.
The 74HCT273 is an example of an octal D flip-flop. It has eight D flip-flops in a single IC package, making it ideal for microprocessor applications. 41