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Altera_Forum's avatar
Altera_Forum
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8 years ago

Flex 10k LPM_ADD_SUB issue

Hi There! Not sure if this has been addressed but instantiating an lpm_add_sub function with carry in- and out under 9.0sp2 (IIRC) for Flex 10K seems to have some peculiar behavior. The add / a...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
8 years ago

Alright, figured it out.. While I blindly duplicated the waveform figures it appears that the carry needs to be inverted for subtraction. This makes total sense when you think about it being two's complement and using the adder, but it's not documented anywhere, as far as I can see..

So yeah, RTFM and watch those waveforms!

-Mux