CSC270 Homework 4 Solution

Exercise #1

Sn Sn+1  G Y R
S0 S1    1 0 0
S1 S2    1 0 0
S2 S3    1 0 0
S3 S4    0 1 0
S4 S5    0 0 1

2 flipflops

Y = Q1.Q2
R = Q0
G = not(Y+R)
D0 = Y
D1 = Q1 xor Q2
D2 = not ( Q0 or Q2)

Exercise #2

The sequencer has 3 modes of operation, depending on the state it starts in.

• The green signal stays on for 3 cycles, then Red turns on, and back to green.
• The Yellow signal blinks, while green and red are off
• The red signal blinks, while green and yellow remain off

Exercise #3

The idea was to generate a sequencer with 6 successive states. During the first 3 states the output is 0, during the last 3 states it is 1. This gives us a period of 6 seconds, and hence a 1/6 Hz signal.

6 states means 3 flipflops.

The equations are:

output signal = Q0
D0 = Q1.Q2 + Q0.(not Q1)
D1 = ( not Q0).(not Q2) + (not Q1).Q2
D2 = not Q2