Sequential Circuit: Counter
Introduction
 Counter is a circuit which cycle through state
sequence
 Two types of counter
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
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
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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
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Sequential Circuit: Counter
Asynchronous Counter (Ripple)
 Example: 3-bit ripple counter
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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
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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 flipflop or JK)
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Sequential Circuit: Counter
Synchronous Counter (Parallel)
 Example: 2-bit synchronous binary counter (using T flipflop or JK) cont….
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Sequential Circuit: Counter
Synchronous Counter (Parallel)
 Example: 3-bit synchronous binary counter (using T flipflop or JK) cont….
YAMANI /ZAILY
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Sequential Circuit: Counter
Synchronous Counter (Parallel)
 Example: 2-bit synchronous binary counter (using T flipflop or JK) cont….
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Sequential Circuit: Counter
Designing Synchronous Counter
 See sequential logic lecture notes
 Example: 3-bit Gray Code Counter (using JK flip-flop)
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Sequential Circuit: Counter
Designing Synchronous Counter
 3-bit Gray Code Counter: flip-flop input
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Sequential Circuit: Counter
Designing Synchronous Counter
 3-bit Gray Code Counter: logic diagram
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