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Sequential Logic

Sequential Logic. By Stephen Voglewede CS 147 2/23/10. What is Sequential Logic?. Combinational Logic. Combinational Logic. The output of a combinational circuit is a function of it’s input. Consequently, it doesn’t matter what the previous output was. Or what the future output will be.

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Sequential Logic

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  1. Sequential Logic By Stephen Voglewede CS 147 2/23/10

  2. What is Sequential Logic?

  3. Combinational Logic

  4. Combinational Logic • The output of a combinational circuit is a function of it’s input. • Consequently, it doesn’t matter what the previous output was. • Or what the future output will be.

  5. Sequential Logic • Input depends on both present input and previous input. • To do this, a sequential circuit must have storage.

  6. Uses • Some types of computer memory • Finite state machines • Other delay and storage elements Because of its ability to store previous input, Sequential circuits are essential components of:

  7. Building Blocks • The basic unit of a Sequential circuit is the Flip Flop. • There are many types of Flip Flops: D, T, JK, SR, etc.

  8. How? • The driving feature of the flip flop is the feedback loop.

  9. How (cont.) This circuit takes advantage of the feedback loop

  10. JK Flip Flop • Origin of name unclear. • Typically represented as a “black box”.

  11. JK Flip Flop (cont.)

  12. JK Flip Flop (cont.) • If Preset P = 0, Q = 1 • If Clear C = 0, Q = 0 • If both are 1, J & K come into play

  13. Input J J J Qc Qa Qb 1 1 1 >Clk >Clk >Clk K K K Qc Qb Qa 1 1 1 In Qc Qb Qa 0 1 2 3 4 5 6 7 0 0 1 0 0 1 0 1 1 1 1 1 1 0 0 0 0 1 0 1 0 1 0 1 0 1 2 Qa 3 4 Qb 5 6 7 Qc JK Clock JK flip flops connected in the toggle mode can be connected together to create a binary counter system. Start with one JK flip flop, apply a clock waveform and sketch the Q output response. Assume PRE and Clr has been disabled (=1) on all flip flops. Qa will toggle on each negative edge of the input clock. Qb will toggle on each negative edge of Qa. Connect a second stage to output Qa. Connect a third stage to output Qb. Qc will toggle on each negative edge of Qb.

  14. Basic Flip Flop

  15. SR Flip Flop

  16. D Flip Flop

  17. T Flip Flop

  18. Master – Slave Flip Flop

  19. Acknowledgements • http://en.wikipedia.org/wiki/File:D-Type_Flip-flop_Diagram.svg • http://computer.howstuffworks.com/boolean5.htm • http://technology.niagarac.on.ca/courses/elnc331/PowerPoint/Lab05.pps • http://wearcam.org/ece385/lectureflipflops/flipflops/

  20. The End

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