# Homework problem: Complete the table for the following sequential circuit.

#### Gonzalo Armbrust

Joined Jun 28, 2015
16
I have to construct a truth table based on the sequential circuit that is given, however i'm incredibly lost as to where to start. ( I have attached a picture of the problem below)

For these types of problems, am I able to start at any input?For example according to the problem, lets say that A=0, B=0, and =1, if I know that B is set to zero, which then gets negated by the NOT gate to 1, and combined with X ( which equals 1), then the output of the logic gate is 1 ( since the output of the gate negated is 1), does this make the next state of A = 1, and also B = 1, since it would still be 1 through the D circuit?

OR

to find the next state value of B, could I just start at A input, and deduce it would be the same value of what A is initially since they are only seperated by a D circuit?

My biggest question for these types of questions is, what input do I start exactly?

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#### crutschow

Joined Mar 14, 2008
23,803
Start with the top of the Truth Table and sequentially solve for each state until you reach the bottom.

#### Gonzalo Armbrust

Joined Jun 28, 2015
16
Start with the top of the Truth Table and sequentially solve for each state until you reach the bottom.
I worked through it, and this is the truth table I came up with, is this correct?

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#### tshuck

Joined Oct 18, 2012
3,535
I worked through it, and this is the truth table I came up with, is this correct?
No. Your first row shows that 0 xor 1 is 0.

Edit: disregard, I mistook the XNOR for XOR.

Last edited:

#### WBahn

Joined Mar 31, 2012
24,974
No need for 1.1 MB files when <22KB will do quite nicely.

Yes, your truth table is correct.

Notice that an XNOR gate with one input negated IS an XOR gate.

#### WBahn

Joined Mar 31, 2012
24,974
No. Your first row shows that 0 xor 1 is 0.
Huh?

It shows that, for B=0 and X=0, the (B') XNOR (X) is equal to 0.

#### tshuck

Joined Oct 18, 2012
3,535
Huh?

It shows that, for B=0 and X=0, the (B') XNOR (X) is equal to 0.
Whoops, my mistake, I didn't realize it was XNOR. That's what I get for trying to check in while in the middle of another task.

#### WBahn

Joined Mar 31, 2012
24,974
Know the feeling -- I'm a lousy multitasker.