Reverse polarity

  • Thread starter EvLer
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  • #1
EvLer
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So, we are just starting ABEL... and I don't quite understand reverse polarity usefullness or application. Here's the extract from my textbook (Wakerly, 3rd ed.):
"In this example, the reverse-polarity equation has one less product term than the normal polarity equation (whatever...the example), so the compiler will select this equation if the targeted device has selectable output inversion." :confused:

could someone explain or give an example how this concept is used... :uhh:
ok, so i understand that compiler will go for a more optimal option, but what does not make sense is that it would select let's say F' over F if F' is more optimal, but the circuit should operate on F not F'! how is this making sense?
Maybe I am asking the wrong question...anyway, I'm confused.

thanks much.
 
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Answers and Replies

  • #2
berkeman
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I believe it refers to the fact that you can write an equation using OR or AND functions to gather up terms. Like:

A & B = !(!A + !B)

In some equations, it may take fewer terms when you use one form or the other, which may help you fit in a smaller CPLD, for example.
 

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