Sequential Logic
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By Stephen Voglewede CS 147 2/23/10
description
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. - PowerPoint PPT Presentation
Transcript of Sequential Logic
By Stephen VoglewedeCS 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.
Sequential Logic
• Input depends on both present input and previous input.
• To do this, a sequential circuit must have storage.
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:
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.
How?
• The driving feature of the flip flop is the feedback loop.
How (cont.)
This circuit takes advantage of the feedback loop
JK Flip Flop
• Origin of name unclear. • Typically represented as a “black box”.
JK Flip Flop (cont.)
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
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.
JK Clock
J
K
Qa
Qa>Clk
1
1
Input
Qa will toggle on each negative edge of the input clock.
Qa
Connect a second stage to output Qa.
J
K
Qb
Qb>Clk
1
1
Qb will toggle on each negative edge of Qa.Qb
Connect a third stage to output Qb. Qc will toggle on each negative edge of Qb.
J
K
Qc
Qc>Clk
1
1
Qc
0 0 0Qc
Qb
QaIn01234567
0 1 2 3 4 5 6 7
0 0 10 1 00 1 11 0 01 0 11 1 01 1 1
Basic Flip Flop
SR Flip Flop
D Flip Flop
T Flip Flop
Master – Slave Flip Flop
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/
The End
