Question

The ripple counter shown in the figure works as a

• A. mod-5-up counter
• B. mod-3-up counter
• C. mod-3-down counter
• D. mod-3-down counter

Answer 1

The correct option is D mod-3-down counter

Trick up/down = CP $\oplus$ Q, 1 for up and 0 for down.
CP = (clock pulse)
Q = (O/P)
0 = - ve edge; Q = 1
1 = + ve edge; $\overline{Q}$ = 1
= 1 $\oplus$ 1 = 0 (down counter)
Counting sequence
1 1 1
1 1 0
1 0 1
1 0 0
0 1 1 (present state) so Mod 5