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Design a 2 bit synchronous up/down counter usign T-flops
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Synchronous up/down counter counts in both ways from 00 to 1 and from 11 to 00. Since, the counter is synchronous, the same clock pulse is given to all T-flipflops.

2-bit synchronous up/down counter

The circuit has an up control input and a down control input.

When the up input is '1', the circuit counts up, since the T inputs recieve their signals from the values of previous normal outputs of the flipflops.

Truth Table:

Selection lines Inputs
A B C D F
0 0 0 0 1 $\begin{align*}F&=C’D’+CD’\\[2ex] &=D’[C+C’]\\[2ex] F&=D’\end{align*}$
0 0 0 1 0
0 0 1 0 1
0 0 1 1 0
0 1 0 0 1 $\begin{align*}F&=C’D’+C’D+CD\\[2ex] &=C’D’+D[C+C’]\\[2ex] &=(D+D’)(D+C’)\\[2ex] F&=(C’+D)\end{align*}$
0 1 0 1 1
0 1 1 0 0
0 1 1 1 1
1 0 0 0 1 $\begin{align*}F&=C’D’+C’D+CD\\[2ex] F&=C’+D\end{align*}$
1 0 0 1 1
1 0 1 0 0
1 0 1 1 1
1 1 0 0 0 $F=CD’$
1 1 0 1 0
1 1 1 0 1
1 1 1 1 0
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