# FSM Diagrams

Discussion in 'Computer Support' started by df, Jan 21, 2007.

1. ### dfGuest

Hi,

Im trying to understand how Finate State Machine diagrams work, I
cant really find alot of info on them.

The one im looking at is here:
http://img261.imageshack.us/img261/9118/clipboard025ds.jpg

I understand that S4 is the 'accepting state' and that S0 is the
'entry state', but I cannot understand what a and b are and what the
purpose of states S2 and S3 are, and more to the point what the FSM
actually does.

Thanks very much for any help,

Jack

df, Jan 21, 2007

2. ### 1932Guest

Some info here J.
http://asicguide.com/verilog/fsm.html

Or you can go to www.google.com , and type in..
Finite State Machine diagrams
^
^ ...i not a.

1932, Jan 21, 2007

3. ### why?Guest

Should be in lots on university computing course notes found online,

http://en.wikipedia.org/wiki/Finite_state_machine

http://cslu.cse.ogi.edu/HLTsurvey/ch11node8.html

I guess the very simple view, is it's how information changes , what
triggers the change and resulting actions.
<snip>

Me

why?, Jan 21, 2007

Blinky the Shark, Jan 21, 2007
5. ### nullius.filiusGuest

a and b are your inputs. (Think of your finite state machine
as a vending machine with a single coin slot that accepts
nickels and dimes, one coin at a time. A mechanical sensor
indicates to the control whether a dime or nickel has been
inserted into the coin slot. If a nickel has been inserted
we get an a, if a dime then a b.)

Your vending machine can only go to S4 if you insert your
coins in the exact sequence a, b, a. Any other possible
input sequence will send you right back to the start. That
is, if you try the sequence a, a, you take the arrow back to
S0; if you try the sequence a, b, b you take the arrow back.
The only allowed sequence is a, b, a. (Reading that
back I sound like the holy handgrenade of Antioch.)

The states remember what you have already done:
* S1 remembers that you have inserted a
* S3 remembers that you have inserted a, b
* S4 remembers that you inserted the sequence a, b, a.

nullius.filius, Jan 22, 2007