1 / 65

Digital Design: Principles and Practices

Digital Design: Principles and Practices. Chapter 8 Sequential Logic Design Practices. 8.4 Counters. Counter. The name counter is generally used for any clocked sequential circuit whose state diagram contains a single cycle, as shown in the next slide (Figure 8-23).

elpida
Télécharger la présentation

Digital Design: Principles and Practices

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Digital Design:Principles and Practices Chapter 8 Sequential Logic Design Practices

  2. 8.4 Counters

  3. Counter • The name counter is generally used for any clocked sequential circuit whose state diagram contains a single cycle, as shown in the next slide (Figure 8-23). • The modulus of a counter is the number of states in the cycle. • A counter with m states is called a modulo-m counter, or divide-by-m counter. • A counter with a non-power-of-2 modulus has extra states that are not used in normal operation.

  4. General Structure of a Counter State Diagram – A Single Cycle

  5. 8.4.1 Ripple Counters

  6. A 4-Bit Binary Ripple Counter

  7. Ripple Counter • A T flip-flop changes state (toggles) on every rising edge of its clock input. • Thus, each bit of the counter toggles if and only if the immediately preceding bit changes from 1 to 0, it generates a carry to the next most significant bit. • Although a ripple counter requires fewer components than any other type of binary counter, it does so at a price – it is slower than any other type of binary counter. • In the worst case, when the most significant bit must change, the output is not valid until time n．tTQ after the rising edge of CLK, where tTQ is the propagation delay from input to output of a T flip-flop.

  8. Synchronous Serial Counter

  9. Synchronous Serial Counter • CNTEN: Master count-enable signal • Each T flip-flop toggles if and only if CNTEN is asserted and all of the lower-order counter bits are 1.

  10. Synchronous Parallel Counter

  11. Synchronous Parallel Counter • Synchronous parallel counter is the fastest binary counter structure.

  12. 2-Bit Asynchronous Counter (LSB) (MSB)

  13. Asynchronous Counters • The clock input of an asynchronous counter is always connected only to the LSB flip-flop. • Asynchronous counters are also known as ripple counters.

  14. 3-Bit Asynchronous Counter

  15. Propagation Delay in 3-Bit Counter

  16. 4-Bit Asynchronous Counter

  17. Asynchronous Decade Counter

  18. Terms • Recycle • the transition of the counter from its final state back to its original state. • Modulus • the number of states • the maximum possible number of states (maximum modulus) of a counter is 2n, where n is the number of flip-flops in the counter.

  19. 74LS93 (4-Bit Asyn. Counter)

  20. 74LS93 (4-Bit Asyn. Counter)

  21. 2-Bit Synchronous Counter

  22. 2-Bit Synchronous Counter

  23. 2-Bit Synchronous Counter

  24. 3-Bit Synchronous Counter

  25. 4-Bit Synchronous Counter

  26. 4-Bit Synchronous Decade Counter • J0 = K0 = 1 • J1 = K1 = Q0Q3 • J2 = K2 = Q0Q1 • J3 = K3 = Q0Q1Q2 + Q0Q3

  27. 4-Bit Synchronous Decade Counter • J0 = K0 = 1 • J1 = K1 = Q0Q3 • J2 = K2 = Q0Q1 • J3 = K3 = Q0Q1Q2 + Q0Q3

  28. The Johnson Counter

  29. 4-bit Johnson Counter

  30. 4-bit Johnson Counter

  31. 4-bit Johnson Counter

  32. 5-bit Johnson Counter

  33. 5-bit Johnson Counter

  34. 5-bit Johnson Counter

  35. The Johnson Counter • In a Johnson counter, the complement of the output of the last flip-flop is connected back to the D input of the first flip-flop. • A 4-bit Johnson counter has 8 states (or bit patterns). • A 5-bit Johnson counter has 10 states (or bit patterns). • In general, an n-bit Johnson counter will produce 2n states.

  36. The Ring Counter

  37. The Ring Counter

  38. The Ring Counter

  39. 8.5 Shift Registers

  40. 8.5.1 Shift-Register Structure

  41. Shift Register • A shift register is an n-bit register with a provision for shifting its stored data by one bit position at each tick of the clock. • Shift Register Structures • Serial-in, serial-out • Serial-in, parallel-out • Parallel-in, serial-out • Parallel-in, parallel-out

  42. Serial-In, Serial-Out Shift Register

  43. Serial-In, Parallel-Out Shift Register

  44. Parallel-In, Serial-Out Shift Register

  45. Parallel-In, Parallel-Out Shift Register

  46. Basic Shift Register Functions • Data Storage • Data Movement • Serial In / Serial Out • Serial In / Parallel Out • Parallel In / Serial Out • Parallel In / Parallel Out • Bi-directional

  47. Shift Register - Data Storage

  48. Shift Register - Data Movement

  49. Serial In / Serial Out Shift Register With four stages, this shift register can store up to four bits of data.

  50. Figure 9–4 Four bits (1010) being entered serially into the register.

More Related