数字电路ch7 Flip-flops.ppt

Common D flip-flops * Chapter 7: Flip-Flops OBJECTIVES After completing this chapter, you should be able to: Explain the operation of a SET-RESET flip-flop. Use a crossed NAND or crossed NOR flip-flop as a debounce switch. Explain the operation of a gated SET-RESET flip-flop. Explain the operation of a transparent D flip-flop. Explain the operation of a D flip-flop used as a latch. Explain the operation of a master-slave D flip-flop. Describe typical IC flip-flops. KEY TERMS CLEAR debounce crossed NAND gated edge-triggered SET-RESET flip-flop flip-flop crossed NAND SET-RESET master-slave D flip-flop flip-flop PRESET crossed NOR SET-RESET SET-RESET flip-flop flip-flop transparent D flip-flop 7.1 INTRODUCTION TO FLIP-FLOPS A flip-flop is a digital circuit that has two outputs Q and Q, which are always in the opposite states. If Q is 1 then Q is 0. and the flip-flop is said to be set, on, or preset. If Q is 0 then Q is 1, and the flip-flop is said to be reset, off, or cleared. There are several types of flip-flops, and the control inputs vary with each type. The logic levels on the flip-flops inputs will determine the state of the Q and Q outputs according to the truth-table for that type of flip-flop. Unlike the gates studied up to this point, the flip-flop can in some states maintain its output state (on or off) after the input signals which produced the output state change. Thus, the flip-flop can store a bit of information or one place of a larger binary number. There are many other uses for flip-flops as we will see in the next few chapters. 7.2 CROSSED NAND SET-RESET FLIP-FLOPS Active LOW Truth table EXAMPLE 7-1 7.3 CROSSED NOR SET-RESET FLIP-FLOPS Figure 7-8 shows a crossed NOR SET-RESET flip-flop. Note that the inputs are not complemented; therefore they are acti