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CSE 271 - Sequential Analysis and Design Practice Problems
K. Dudeck
1)
Q
A
Q'
A'
Q
B
Q'
B'
D
X
CLK
Y
D
CLK
CLOCK
Analyze the circuit above, and determine the characteristic input equations DA and DB.
Then determine the state table and state diagram.
2) Given a sequential circuit with the following flip flop input equations and output function:
JA  BX  B Y
KA  BX Y
Z = AXY + B X Y
JB  AX
KB  A  X Y
a) Draw the diagram of the circuit.
b) Determine the state table and the state diagram.
c) If both flip flops are initially RESET, and inputs X and Y are both HIGH, what is the
state of the circuit and the output three clock pulses later?
3) A sequential circuit has three flip flops A, B, C, one input X, and one output Y. Design the
circuit so that it has the state diagram shown on the next page. Use D flip flops. Make sure the
circuit is stable (self correcting).
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4) Suppose you have to build the circuit shown in problem #1, but you only have J-K flip flops.
Redesign the circuit so it operates the same way, but uses J-K flip flops instead.
5) (Real world problem) There is an elevator in a sixteen story office building. You must design a
sequential control circuit for the elevator that uses D-flip flops. Your circuit has two available
inputs: an input, X, which is true when then elevator is on the desired floor, and an input, Y,
which is true when the elevator is below the desired floor and must move up.
One flip flop output, M, will go to a motor, which will run when the output is true.
Another flip flop output, T, will go to a transmission, which controls the direction of the motor,
up or down. When T=0, the motor will move down when M=1, and when T=1, the motor will
move when M=1. One characteristic of motors is that they do not like to have their direction
changed while they are running.
Your control circuit should operate in the following manner:
1) If X=1, then leave the state (MT) unchanged.
2) If XY=00, the motor must move downward.
3) If XY=01, the motor must move upward.
If the motor must change direction, it must first be turned off, the direction changed, then
the motor turned on.
Design the circuit by drawing a state diagram which satisfies the problem. Then generate
the state table, and finally, draw the circuit which will satisfy this design.