1. Sequential Circuit: Counter
Introduction
Counter is a circuit which cycle through state sequence
Two types of counter
Synchronous counter (e.g. parallel)
Asynchronous counter (e.g. ripple)
Ripple counter let some flip-flop output to be used as clock signal source for other flip-flop
Synchronous counter use the same clock signal for all flip-flop

2. Sequential Circuit: Counter
Asynchronous Counter (Ripple)
Example: 2-bit ripple counter
Output from one flip-flop is connected to clock input for the next flip-flop MSB

3. Sequential Circuit: Counter
Asynchronous Counter (Ripple)
Example: 3-bit ripple counter

4. Sequential Circuit: Counter
Asynchronous Down Counter
The previous example is up asynchronous counter
Down asynchronous counter count from large to zero and repeat
Example: 3-bit binary down counter

5. Sequential Circuit: Counter
Synchronous Counter (Parallel)
Synchronous counter: flip-flop with the same synchronous clock signal
We can build synchronous counter using process to design sequential circuit
Example: 2-bit synchronous binary counter (using T flip-flop or JK)

6. Sequential Circuit: Counter
Synchronous Counter (Parallel)
Example: 2-bit synchronous binary counter (using T flip-flop or JK) cont….

7. Sequential Circuit: Counter
Synchronous Counter (Parallel)
Example: 3-bit synchronous binary counter (using T flip-flop or JK) cont….
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8. Sequential Circuit: Counter
Synchronous Counter (Parallel)
Example: 2-bit synchronous binary counter (using T flip-flop or JK) cont….

9. Sequential Circuit: Counter
Designing Synchronous Counter
See sequential logic lecture notes
Example: 3-bit Gray Code Counter (using JK flip-flop)

10. Sequential Circuit: Counter
Designing Synchronous Counter
3-bit Gray Code Counter: flip-flop input

11. Sequential Circuit: Counter
Designing Synchronous Counter
3-bit Gray Code Counter: logic diagram