ECE 271 Homework #7
PROBLEM #5 HAS BEEN CORRECTED
1. (1 point) What is an exhaustive test?
A test where all possible unique test patterns are applied to a CUT
2. (3 points) A combinational logic circuit has 18 binary inputs. Assuming it
takes 50 s to input one test pattern and record the circuit’s output, how long
will it take to do an exhaustive test?
218 x 50s
3. (1 point) What is a “stuck-at” fault? Show an example of a stuck-at 0 fault.
Any node in a circuit that is inadvertently connected to logic 0 or logic 1. An example
would be the output of an XOR gate that is accidentally shorted to ground.
4. (1 point) What are the two problems with trying to conduct an exhaustive
test?
Takes too long (problem #1). Because of that, you have to use only a subset of the
tests to shorten the test time. But how do you choose a subset that maximizes fault
coverage? (problem #2)
5. (3 points) Consider the circuit in figure 4-31 in your textbook. You have
picked a test pattern set that is capable of 89% fault coverage. How many
faults can your test pattern set detect? (Assume the circuit is only
susceptible to stuck-at-faults.)
There are 12 possible points where stuck-at faults can occur. Assuming only one
stuck-at fault can occur at one time, there are 24 possible stuck-at faults. This means
your test pattern set could detect 0.89 x 24 = 21 faults. If you assume any number of
stuck-at faults can occur, then there are 212 = 4096 312 - 1possible faults. In that
case, you could detect approximately 3645 0.89*(312 -1) faults.
6. (1 point) A circuit design was recently completed and sent to manufacturing
to start building them. You now believe the circuit will not meet one
specification. You discuss this with one of your fellow engineers and she tells
you to “not make waves” and don’t bother to tell anyone because it will just
be more work for everyone. Do you agree? (Why or why not?)
NO!!! To ignore this would be unethical.