# Algorithmic State Machine using D flip Flops - how to deal with don't care conditions

I have the following state transition table:

where,
A, B - current states of two D flip flops

A+, B+ - next states of the two D flip flops

X1, X2, X3 - inputs to the current states

There are don't care conditions in inputs X1, X2 and X3.

I am trying to make a K-map for A+ using four variables A, X1, X2 and X3. I have dealt with don't cares in the output. But, I don't know how to deal with don't cares when they are on the input side.

How to deal with input don't care conditions ?

(I somehow tried to solve and got the answer: A+ = A'*X2'. Answer key has something else the answer. My state transition table is same as the one given in the answer key. So, I am sure that my state transition table is correct. I am sure that I am making mistakes in building K-maps from table as I don't know to incorporate input don't cares.)

• The A+ K-Map needs to have 5 variables, A, B, X1, X2 and X3 Nov 22, 2015 at 10:06
• The B+ K-Map also needs 5 variables. The next state of both flops depends upon the current state of both plus the inputs. Nov 22, 2015 at 10:57