1. Sequential logic circuits

2. Sequential logic circuits
Outline
Sequential Circuit Models
Asynchronous
Synchronous
Latches
Flip-Flops
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Sequential logic circuits

3. Sequential logic circuits
The main characteristic of combinational logic circuits is that their output values depend on their present input values.
Sequential logic circuits differ from combinational logic circuits because they contain memory elements so that their output values depend on both present and past input values
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Sequential logic circuits

4. Sequential logic circuits
Sequential circuits can be Asynchronous or synchronous.
Asynchronous sequential circuits change their states and output values whenever a change in input values occurs.
Synchronous sequential circuits change their states and output values at fixed points of time, i.e. clock signals.
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Sequential logic circuits

5. Sequential Circuit Models
Universal model
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Sequential logic circuits

6. Sequential logic circuits
Combinational circuit model
Mealy machine model
Moore machine model
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Sequential logic circuits

7. Sequential logic circuits
Memory Devices
Latches A latch is a memory element whose excitation signals control the state of the device. A latch has two stages set and reset. Set stage sets the output to 1. Reset stage set the output to 0.
Flip-flops A flip-flop is a memory device that has clock signals control the state of the device.
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Sequential logic circuits

8. Sequential logic circuits
Latch
Flip-flop
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Sequential logic circuits

9. Sequential logic circuits
Inverter Chains
Ring oscillator
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Sequential logic circuits

10. Sequential logic circuits
Latches
RS Latch
The RS latch is the basic memory element consists of two cross-coupled NOR gates. It has two input signals, S set signal and R reset signal. It also has two outputs Q and Q'; and two states, a set state when Q = 1 and a reset state when Q = 0 (Q' = 1)
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Sequential logic circuits

11. Sequential logic circuits1 S R Q
hold 1
0 reset
1 set
unstable
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Sequential logic circuits

12. Sequential logic circuits1 S R Q
unstable 1
0 reset
1 set
hold
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Sequential logic circuits

13. Sequential logic circuits
Flip-Flops
A flip-flop is a level-sensitive latch with a clock input.
RS flip-flop
Q+ = S +R'Q
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Sequential logic circuits

14. Sequential logic circuits
T (Toggle) flip-flop D
Q(t)
Q(t+1)
Hold 1
Toggle
Q+ = TQ' + T'Q
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Sequential logic circuits

15. Master Slave Flip-Flops
A master slave flip-flop consists of two latches and an inverter.
Master-slave RS flip-flop
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Sequential logic circuits

16. Master-Slave JK Flip-Flops
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Sequential logic circuits