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Altera_Forum
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13 years ago

Subtraction with numeric_Std doesn't work

Hello What am i doing in wrong in the code below. subtraction doesn't work! I am using numeric_std and the numbers are in twos complement format. // mattgust library ieee; use ieee....
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
13 years ago

The testbench shows that the ALU works perfectly. The result is always right. But I'm sure the overflow detector is wrong. You didn't post the code. The problem is in the substraction. Look at the the first sub: -128 - ( +2) = -130. But you can't store -130 in 8 bits. So it's an overflow. Signal overflow should be '1'.