Page 169 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Digital Circuits and Logic Design

Notes The circuit has
• Clock input, CP.
• One input x
• One output y
• One clocked JK flip-flop
• One clocked D flip-flop (the machine can be in maximum of 4 states)
A State table is representation of sequence of inputs, outputs, and flip-flop states in a tabular form.
Two forms of state tables are shown in Table 10.1, (the second form will be used).
Table 10.1: State Table Form 1

Next state Output
Present state
x = 0 x = 1 x = 0 x = 1
A B A B A B y y
0 0
0 1
1 0
1 1

Analysis is the generation of state table from the given sequential circuit.
The number of rows in the state table is equal to 2 (number of flip-flops+ number of inputs) . For the circuit under
consideration, number of rows = 2( 2 + 1) = 2 = 8
(3)
Table 10.2: State Table Form 2

Present state Input Next state Output
A(t) B(t) X A(t + 1) B(t + 1) y
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1

In the present case there are two flip-flops and one input, thus a total of 8 rows as shown in the
Table 10.3.
Table 10.3: State Table

Present state Input Next state Output
A(t) B(t) X A(t + 1) B(t + 1) y
0 0 0 0 0 0
0 0 1 0 1 0
0 1 0 1 0 0
0 1 1 0 1 0
1 0 0 0 0 0
1 0 1 1 1 0
1 1 0 1 0 0
1 1 1 0 1 1

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