Negation of 8-bit hexadecimal
Use the same formula as you do for two's complement. First, compute the complement of the number by complementing all letters. Then add 1. Complementing works using the following table:
$$
0 \leftrightarrow F, 1 \leftrightarrow E, 2 \leftrightarrow D, 3 \leftrightarrow C, 4 \leftrightarrow B, 5 \leftrightarrow A, 6 \leftrightarrow 9, 7 \leftrightarrow 8.
$$
Example: starting with 0000BDDA, we first get FFFF4225, and after adding 1, we get FFFF4226.

Why does this work? Exercise.