MadeEasy Test Series: Digital Logic - Digital Counter

Question

What is the best architecture of the ‘Logic gate’?

• a 3-bit input AND gate
• a 2-input AND gate
• a NOT gate
• a wire connection (no logic gate needed)

Comments

is it a wire connection(no logic gate needed)?

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yes option d

Answer 1

 its up counter , in 4th clock pulse, we need to make Q3 bit as 0 in order to get mod 4 counter. so, NOT gate is required as clear inputs are active low.

Clock	Q3	Q2	Q1
0	0	0	0
1	0	0	1
2	0	1	0
3	0	1	1
4	1	0	0

Answer 2

as this is asynchronous circuit Q0n= Q0' for every signal

Q1n= Q1' (for Q0 1->0 transaction as its negative edge trigger )

Q2n=Q2' (for Q1   1->0)

Q0	Q1	Q2	Q0n	Q1n	Q2n
0	0	0	1	0	0
0	0	1	1	0	1
0	1	0	1	1	0
0	1	1	1	1	1
1	0	0	0	1	0
1	0	1	0	1	1
1	1	0	0	0	1
1	1	1	0	0	0

so 000->100->010->110-> 001 when Q2 is 1 it will clear and maintain mod 4 properties  so here directly Q2 gives 1 after 4 state so direct connection is enough ,no logic is needed .