counter
I want to build a counter circuit which to count from from 0-7, during some pulseswidth. The problem I am having is that it has to do the whole count sequence during one PW and that is where I am struggling to come up with an idea
edit: just want to delete question now, sorrry for irrelevance and being unclear
The key points are:
Ensure that after gating the new arrangement makes logical sense. ie why should it count DOWN now. If you don't follow the logic of what you think it should do then you can't be too surprised if it disagrees with you :-)
Always change over in a "neutral" state. Ensure that clock lines or other state relevant lines are in a condition before and after the change that will not cause a transient change of state.
A marvellous (& free) tool
Logisim - an educational tool for designing and simulating digital logic circuits
They say:
It sounds like you don't have an external reset signal to respond to, you just want to count to some number then go to zero as the next step. You could consider this a mod n counter, where n is one more than the maximum count in your counter.
So I'm not sure what you mean about "losing a signal" while doing the reset. If you had a 3-digit decimal counter and it rolled over from 999 to 000, you wouldn't consider it as "losing a signal", it would just be counting to the next value in mod-1000 arithmetic.
So if you do
always @(posedge clock) begin
if (counter == some_number) begin
counter <= 0;
end
else begin
counter <= counter + 1;
end
end
You'll have a counter that counts continuously in mod-some_number+1 arithmetic. Alternately you could say it counts to some_number, then resets to zero without ever "losing" a clock pulse.
If some_number+1 happens to be a power of 2, you don't even need the reset condition in your code. For example, for a mod-16 counter, you can just use a 4-bit counter, and the synthesized logic will count continuously and repeatedly from 0 to 15.
Best Answer
You say you are not allowed to use counter ICs..... How about making a counter IC?
Counters are made up of flip flops in series with each other. Flip flops can be made with logic gates, or if you are not allowed to use them either, they can be made with transistors. This would solve your LED sequence problem.
As for being able to do the whole thing during one high pulse.... you would have to build a small circuit that would oscillate 7 times during one pulse width to trigger your home made counter.