# Problem with digital electronic

#### dl324

Joined Mar 30, 2015
13,822
If he REALLY needs to do this asynchronously, I would recommend making a simple mod-12 ripple up counter and then decode the outputs to get the desired sequence.
He wants count down from 15 to 4, but that's what I did; on Friday. I did it with positive and negative clocked flip flops since he didn't say which he was supposed to use...

#### Beginner0001

Joined Sep 29, 2017
18
If I understand you correctly, the first group is for the current state and the second group is the next state?

If so, then you are saying that from State 15 you are going to go to State 4. Is that what you want?

Yes, you understood right.
Like is shown at table, first state is state 15, next is state 4, because i think that's how down counter works.

#### dl324

Joined Mar 30, 2015
13,822
Like is shown at table, first state is state 15, next is state 4, because i think that's how down counter works.
That's your first problem. A count down counter counts down. So from 15, the next count would be 14.

#### Beginner0001

Joined Sep 29, 2017
18
Ok, so this should be right.

I just don't understand what state is after 4.

#### dl324

Joined Mar 30, 2015
13,822
I just don't understand what state is after 4.
What would a count down counter normally do when it counts down to it's minimum count?

The answer was given in an earlier post.

#### WBahn

Joined Mar 31, 2012
26,398
Yes, you understood right.
Like is shown at table, first state is state 15, next is state 4, because i think that's how down counter works.
If I count down from three, wouldn't you expect me to go, "Three, two, one, GO!" or something similar?

#### Beginner0001

Joined Sep 29, 2017
18
If I count down from three, wouldn't you expect me to go, "Three, two, one, GO!" or something similar?
Ok, i understan it now, i was confused probably because it starts with 15 and my profesor obisaly didn't explaind it very well.

What would a count down counter normally do when it counts down to it's minimum count?

The answer was given in an earlier post.
Counter will start from beginning. So after state 4 is state 15?

#### dl324

Joined Mar 30, 2015
13,822
Ok, i understan it now, i was confused probably because it starts with 15 and my profesor obisaly didn't explaind it very well.
Consult the datasheet for any counter and see what the typical behavior is. There are no commercial mod-12 counters because there isn't a general need, but there are many examples of decade and binary counters.
Counter will start from beginning. So after state 4 is state 15?
That's what I'd assume. If you have questions regarding expectations, you should ask your professor.

#### WBahn

Joined Mar 31, 2012
26,398
Ok, i understan it now, i was confused probably because it starts with 15 and my profesor obisaly didn't explaind it very well.

Counter will start from beginning. So after state 4 is state 15?
Unless told otherwise, that's about the only reasonable assumption to make.