# State table and state diagram

Discussion in 'Homework Help' started by baumerman, Oct 15, 2012.

1. ### baumerman Thread Starter New Member

Oct 11, 2012
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0
Hi guys,

Last question I will have for a while.. I'm signing up with a tutor next week because I feel like a lot of this is beyond me.

Anyway, here is the final one I am stuck on:

A sequential circuit has one flip-flop Q, two inputs X and Y, and one output S. The circuit consists
of a D flip-flop with S as its output. The input D of the flip-flop is defined as follows:

D = X XOR Y XOR S

1. Derive the state table
2. Derive the state diagram

Any input or guidance would be super helpful! Cheers

2. ### WBahn Moderator

Mar 31, 2012
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You have three signals that dictate what state you will move to next (if you move at all).

You only have one memory element, so you only have two possible states (with the output of the DFF defining which state you are in).

Simply make a table of all the possible state transitions. Organize it as two tables -- one for when you are in one state and one for when you are in the other. Then determine, for each of the possible values of the inputs, which state you will transition to next.

Based on this, you should be able to draw your diagram. You have two states (circles) and two possible transitions for each state -- either transition to the other state or stay in the same state. Label these arrows with the input combinations that cause each to happen.

Nov 25, 2009
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