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Altera_Forum's avatar
Altera_Forum
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13 years ago

when use 'else' and when use ; ?

Hi.. I am starter in VHDl. I have some questions... What is difference between else and ;? first code use else but when i use ';' instead of 'else' it doesn't work. Do you know why? and s...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
13 years ago

Your assignment to a is done outside a process, so imagine that it happens (nearly) instantly. (instead of conditionally).

The assignment to a is using more of a priority list to determine your output. If i(7) = '1', it doesn't matter what 6-0 are, your output will be "111". If i(7)=0, then i(6) is examined next. If you re-wrote your statement as:

a<="000" when i(0) = '1' else

"001" when i(1) = '1' else

..

"111" when i(7) = '1' else

"000";

then i(0) = '1' would take priority over all others.