# Synchronous Counter Mod-12 Up/Down Exercise

## Homework Statement

"Design a Synchronous Counter Mod-12 Up/Down, using only Flip-Flop Type D. A binary input $U$ that determines if the counter has to increase ($U = 1$) or decrease ($U = 0$).

## Homework Equations

Flip-Flop Type D equation is
$Q_{t + 1} = D$

## The Attempt at a Solution

I have done already this type of exercise but without the Up/Down. How should it be now? Do I have to add a column $U$ when I write the table? Like for example:
$q_3 q_2 q_1 q_0 | q_3' q_2' q_1' q_0' | D_3 D_2 D_1 D_0 | U$
$0 0 0 0 | 0 0 0 1 | 0 0 0 1 | -$
$0 0 0 1 | 0 0 1 0 | 0 0 1 0 | -$
etc.
And in that column, when do I have to write $1$ and when $0$ since it is up to the one that uses the counter? Or I write all "don't care" in the column? But wouldn't that be pointless?

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