Assembly Language Programming

Assignment #6

Combinational Circuits

1. A circuit with two inputs is to be constructed using AND, OR and NOT. The truth table is:

x y | out
----|----
0 0 | 1
0 1 | 1
1 0 | 0
1 1 | 1

This function is called implication. Show the sum of products (DNF) formula that is related to this table. Draw a combinational circuit to implement the desired functionality.

2. Build the truth table for the following circuit (please excuse the ragged drawing).

3. Design a single-bit subtraction circuit. Inputs are x, y, and bi (borrow in). There are two outputs: d (= x-bi-y) and bo (borrow out = true when y > (x-bi)). Draw the truth table and logic diagram.

4. Implement a "majority rule" function for three inputs. This circuit outputs a 0 if more inputs are 0 and a 1 if more inputs are 1. Start with a truth table and derive the DNF formula. See if you can simplify the formula using the rules of logic. Draw a circuit from the simplified formula.