Two's Complement

Remember that the scheme two's complement can represent both positive and negative integers.

Since this problem calls for eight bits, put another bit on the left. The eight-bit two's complement representation of positive 85 is 01010101.

Now form the negative of that by reflecting the bits and then adding one. Here is the reflection:

01010101       original

10101010       reflected

Here is one added to the reflected pattern:

10101010
     + 1
--------
10101011      ← representation of -85 in eight-bit two's complement