We know that, Excess-3 code begins with the binary 0011(decimal 3) and it will continue up to binary 1100(decimal 12) where I get the output binary 1001(decimal 9) for input binary 1100(decimal 12). So I need 4 variables as inputs and 4 variables as outputs. With 4 variables I can represent 16 binary values from 0000 to 1111. Since I do not use 0, 1, 2, 13, 14, 15 as inputs, when I simplify the output function I use those terms as don’t care conditions.
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it really helped !! thanks