Digital Circuit Fundamentals 1 Unit 6 – 4-BIT Comparator
Exercise 2 – Modulus Control
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to set the modulus of a counter with a
comparator. You will verify your results by using a comparator to drive the CLEAR input of a
synchronous counter.
DISCUSSION
- The LS85 comparator outputs generate time slots that reflect the relationship between two 4-
bit words. - When a comparator output signal is wired to the CLEAR input of a counter, the signal can be
used to reset the counter once a predetermined binary value has been reached. - Controlling the binary value of word A while word B cycles between binary values generates
comparator outputs which are active for a specific period of time. By selecting the
appropriate output the comparator can control the modulus of the counter.