I have two 2's complement signed binary numbers and want to subtraction them (assuming an 8-bit subtractor)
1001 0110
1000 0001
what would be the operation to find the difference and why/whynot is there an overflow
to get the difference between 2 numbers you have to subtract them:
1001 0110b = -106
1000 0001b = -127
so -106 - (-127) = 21
you can also do that in binary:
1001 0110b
-1000 0001b
=
0001 0101b
another method is: a-b = a+(-b), so you have to make the 2's complement of the second number. So 1000 0001b becomes 0111 1111b.
1001 0110b
+0111 1111b
=
1 0001 0101b
the first 1 doesn't count because it's a 8bit number, so the result is also 0001 0101b which is 21 in decimal.