FAQ - State Machines

Q1: What is the notation of arcs in a state machine?

Q2: What's the difference between a comma and semicolon?

Q3: How does the the Coke machine handle bad coins?

Q1:
I am working state machines test questions and practice problems. Can
you please clarify the notation used between states. I am confused
when and how we are to represent the inputs and outputs between
states. You're practice exam uses null to represent a 0 input value
and the input (i.e. Y) when it is "don't care". The outputs that are 0
are left off.

When an arc is labeled on a state diagram, the left of the slash is
the asserted inputs; the right of the slash is the asserted outputs.
Null implies that their are no asserted values.

Q2:
I am working on the 1999 practice test and am stuck on the state
machine question. How do we know when to use a null;"something else"
as the input? Why are some of the input arguments separated with
semicolons and others are not?

Normally, if multiple inputs are asserted, their are comma separated.
If two arcs have the same start state, the same ending state, and the
same asserted outputs, the can be combined and the inputs are listed
separated by semicolon.

Q3:
I was looking at your notes for state machines. In the case of the 15
cents Coke machine, the output rejected when 5cents is 1, and 10cents
is 1. Just to be sure, people are inserting them both at the same
time, aka bad coin?

Both signals from the change box (N and D) are asserted when it
detects an invalid coin (slug, penny, etc.) So this coin should be
rejected.