Well a 4 bit counter is 2^4 or 0 to 15 in count. Actually a count up of 0 to 15 or count down 15 to 0. So when we make the statement:
I need it to be Up'/Down = 0 then the circuit should behave as an up counter. If Up'/Down = 1 then the circuit should behave as a down counter.
So if the count = 1 You want to count down to 0 but what if the count is greater than one like 2, 3, 4 or greater? Thus for example we have equal to or greater than which I thing is what you want, that would be:
If my.count >=1 then
count.down
The result would be a Boolean as in a 1 or 0. More operator examples:
= test for equality, result is boolean
/= test for inequality, result is boolean
< test for less than, result is boolean
<= test for less than or equal, result is boolean
> test for greater than, result is boolean
>= test for greater than or equal, result is boolean
If I have time later today at work I'll try to give you a few examples.
<EDIT> Actually a good example of a SYNCHRONOUS 4-BIT UP/DOWN COUNTER is a counter like the 74193 series.
This is the data sheet and the data sheet provides full logic drawings breaking the chip down. Try to follow the logic and read the description of what the chip does. That should help you out. </EDIT>
Ron