Simulink ADD block keeps returning 255
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Byron Piper on 11 Dec 2022
Answered: Andy Bartlett on 13 Dec 2022
So I have two inputs 'Pre-State' and 'Pre-Status'. The values going into the ADD block are '1' and '0' respectively, yet for some reason the ADD block keeps returning 255.
The ADD block is setup so that 'Pre-Status' is subtracting 'Pre-State'. So in theory, the output should be -1. Yet it keeps giving 255 for some reason.
Fangjun Jiang on 12 Dec 2022
Some settings are not right. You have to show it. I guess it is the data type of the output and the saturation flag.
Andy Bartlett on 13 Dec 2022
My guess is that Sum block's output data type is uint8, and the block is configured to wrap on integer overflows.
So the output would be module 2^8 of the "ideal output result".
idealOutput = -1
actualOutput = mod(idealOutput, 256)
We could also test this theory with Fixed-Point Designer fi objects.
nt = numerictype('uint8')
fiOutput = fi( idealOutput, nt, 'OverflowAction', 'Wrap', 'RoundingMethod', 'Floor')
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