8-bit adder with carry and LCD panel

Warning: VERY SLOW. N1 + N2: input N1, N2, set bottomright bit to 0. Red led ON = result exceeds 8 bits (carry bit). N1 - N2: input N1, ¬N2, set bottomright bit to 1. Red led ON = no borrow occurred. In this example: 45-19=26.