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Altera_Forum's avatar
Altera_Forum
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14 years ago

signed to unsigned

i, i want to convert a 10 bit signed into a 8 bit unsigned. i tried with the altbus, but when implemented if i input -32 i get FF instead of 0. Is there an other block? which settings i have to m...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
14 years ago

Ok, I checked my simulation again and could reproduce your results after enabling the saturation in the Altbus block. And you are right the simulation produces '0' as output but already a VHDL simulation showed 255 (decimal) or 0xFF (hex). What is a result I would expect.

To explain this here what happens:

input to AltBus:

-32 (10 bit signed decimal) = 11 1110 0000 (binary) = 0x3E0 (hexadecimal)

convert to unsigned

992 (10 bit unsigned decimal) = 11 1110 0000 (binary) = 0x3E0 (hexadecimal)

saturate, then 992 > 255:

255 (8 bit unsigned decimal) = 1111 1111 (binary) = 0xFF (hexadecimal)