## PHYS345 Electricity and Electronics

**Hint for P9.18**
Construct a truth table with three inputs, A, F, and B_{i} and two outputs,
D and B_{o}.

Think back to elementary subtraction facts:

A=1, F=1, B_{i}=0: With no borrow input, 1-1=0 and no borrow output. Right?

A=0, F=1, B_{i}=0: With no borrow input, 0-1=1 with the borrow output set.

A=1, F=0, B_{i}=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.

"http://www.physics.udel.edu/~watson/phys345/protected/exercises/hints/P9-8a.html"

Last updated Oct. 30, 1998.

Copyright George Watson, Univ. of Delaware, 1998.