Page 120 - Handout Digital Electronics

Workings: Step 1

From the problem specifications produce state table

Present State Input Next State
A B X A B
0 0 0 0 0
0 0 1 0 1
0 1 0 0 1
0 1 1 1 0
1 0 0 1 0
1 0 1 1 1
1 1 0 1 1
1 1 1 0 0
From the state table produces the state diagram according to the sequential circuit specification, this
circuit has no external outputs.

00
11

X = 1
X = 1

X = 0

01 x = 1 x= 0
10

Figure 52: 2-bit binary counter state diagram

Step 2 From the state diagram, produce the excitation table. Since the sequential circuit is a binary
counter, we will use two JK flip flops to build a 2- bit binary UP counter

Present State Input Next State JK flip Flop Inputs
A B X A B JA KA JB KB
0 0 0 0 0 0 x 0 x
0 0 1 0 1 0 x 1 x
0 1 0 0 1 0 x x 0
0 1 1 1 0 1 x x 1
1 0 0 1 0 x 0 0 x
1 0 1 1 1 x 0 1 x
1 1 0 1 1 x 0 x 0
1 1 1 0 0 x 1 x 1
JA and KA are the inputs of flip flop A and JB and KB are the inputs of flip flop B

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