Thursday May 26

We will continue reviewing Chapter 3 on Combinational Logic Design.

Also, today I really will collect Lab 2 and Assignment 1 for marking.

For this week’s assignment, answer question 3-6 from the text book. Your answer to Assignment 2 is due on Thursday June 2.

Assignment 2

Q 3-6. A low-voltage lighting system is to use a binary logic control for a particular light. This light lies at the intersection point of a T-shaped hallway. There is a switch for this light at each of the three endpoints of the T. These switches have binary outputs 0 and 1 depending on their position and are named X1, X2, and X3. The light is controlled by a buffer driving a thyristor, an electronic part that can switch power-circuit current. When Z, the input to the buffer, is 1, the light is ON, and when Z is 0, the light is OFF. You are to find a function Z=F(X1, X2, X3) so that if any one of the switches is changed, the value of Z changes, turning the light ON or OFF.

Express the function using only NAND gates and invertors (NOT gates).

Hint: Draw a truth table with inputs X1, X2, X3 and determine if the if the light should be on or off as the switches are operated.

Wednesday May 25

As a result of the holiday on Monday, we will start reviewing Chapter 3 on Combinational Logic Design in place of the Lab today.

A reminder that I will be available during office hours today.

In addition, both Lab 2 and Assignment 1 are is due today.

Update: Submission of Lab 2 and Assignment 1 is extended to Thursday. I’ll go through this in class today.

Assignment 1 and Lab 2

Assignment 1

A few hints might be helpful.


In general, start by expanding into standard form (every term having all variables), then rearrange, expand (using the identity x = x+x) and finally factorize. It is helpful to draw the Karnaugh maps to determine the prime implicants and use this to guide the factorization.

With Q2-6 b), simply use De Morgan’s law.


Drawing out the Karnaugh map allows simplifying of the expression. The inverse function can also be expressed identifying where the values are 0 and then using De Morgan’s law to express it in the product of sums (POS) form.


Nothing more to add – it is straight forward.

Lab 2

A reminder that the files submitted online must be your own individual work. My plagiarism test will reveal any files that have been copied from others.

Thursday May 19

Today we will  review optimization using Karnaugh Maps, then complete chapter 2 on Combinational Logic Circuits.

You will receive the first assignment to practice Boolean algebra and Karnaugh Map optimization, which is due on Wednesday May 25.

Monday is a holiday and the college is closed. As a result the due date for this week’s Lab work is also extended to Wednesday May 25.

Wednesday May 18 – Lab 2

In this week’s Lab we will design and implement a simple combinational logic circuit.

Lab 2 can be downloaded and printed. When completed it should be handed in no later than our class on Monday along with submitting your circuit online.

LogicWorks should be available on all computers in Columbia College.

A reminder if you want to use LogicWorks on your own PC at home then you can buy a copy of LogicWorks 5 Software from the supplier or you can get the LogicWorks 5 Textbook that comes with a software install CD.