PHYS345 Electricity and Electronics

Hint for P9.18

Construct a truth table with three inputs, A, F, and Bi and two outputs, D and Bo.

Think back to elementary subtraction facts:
A=1, F=1, Bi=0: With no borrow input, 1-1=0 and no borrow output. Right?
A=0, F=1, Bi=0: With no borrow input, 0-1=1 with the borrow output set.
A=1, F=0, Bi=1: With the borrow input set, 1-0-1=0 with no borrow output.
Determine the rest of the truth table entries.

Convert to two Karnaugh maps, one for each output. Follow the textbook's example for the full adder.

Last updated Oct. 30, 1998.
Copyright George Watson, Univ. of Delaware, 1998.