Simple $4-$bit Arithmetic Logic Unit $($ALU$)$: $4$

This circuit selects between arithmetic $($absolute B

value of difference, addition$)$ and logical $($NOR$,$ NAND$)$ operations. Only one result $($hexadecimal value$)$ can be shown on the $7-$segment display. This is selected by the input sel$(1.\mathrm{.}0).$

$$ Arithmetic operations: The $4-$bit inputs A and B