## PHYS345 Electricity and Electronics

**Hint for P9.21**
Determine how one row of D's leads to the next row of Q's in the truth table -
remember that this is *sequential* logic.
You may study Table 9.1 in the textbook
which is a truth table for a different counter.

Note also that there are four inputs: the enable bit E and the three data bits,
D_{1}, D_{2}, and D_{3}.
There are three outputs: Q_{1},
Q_{2}, and Q_{3},
not four as claimed in the last sentence of the problem statement.
The objective is to derive the D's for the subsequent state from the Q's for the current state.

Construct Karnaugh mapping of EQ_{3}\Q_{2}Q_{1}
to find the combination of gates needed to derive the D's from the Q's,
similar to the process on pg. 253 of the textbook.

"http://www.physics.udel.edu/~watson/phys345/protected/exercises/hints/P9-21.html"

Last updated Nov. 6, 1998.

Copyright George Watson, Univ. of Delaware, 1998.