CS 231 Fall 2005 Review Session

CS 231Fall 2005Review Session Friday, Oct 21 by Celal Ziftci

Today’s topics • How to distinguish between different kinds of circuits? (Combinatorial, Latch, Flip-flop) • How to find the timing diagram of a given circuit (with gate delays)? • How to design a sequential circuit, for a given problem definition?

1. There is a combinatorial circuit, a flip-flop and a latch with control. Which is which?

2. Given the following circuit and initial input values…Gate delay = 1 ns

2. Sequential Circuit Design • Problem definition: Implement a circuit which outputs 1 only if the # 1’s in the input string is a multiple of 4. • Ex:Input 0 1 0 0 1 1 1 0 0 1 Output  1 0 0 0 0 0 1 1 1 0

Observation:We can rewrite the problem as follows:Output 1 when: (X % 4) = 0 (X is the number of 1’s so far). • So we don’t need to remember the whole string. We only need to remember (X % 4). • We have 4 possibilities: 0, 1, 2, 3

Using the state diagram, we can construct our state table…

After this point, we can draw K-maps for J1, K1, J0, K0 and output, and we are done!

All for today. • If you have any questions, come to any TA office hours.

CS 231 Fall 2005 Review Session