the ISR: is just the serial interrupt.
a state machine is an effective way of controlling different events and stages. A state machine has a limited number of states. And it does not do a thing unless a new state is detected.
Like a traffic light. This could be done using a state machine as well.
for example the light is green, then it goes orange and then red. after red, it becomes green again (it depends on the country).
so you could program it like this :
dim state as byte
do
select case state
case 0 : 'nothing done yet so we set all leds off
green=0 : red=0 : yellow=0
state =1
case 1 : 'the first state would be green
green=1 : state = 2
case 2 : wait 3 : state =3 'wait some time
case 3 : orange=1 'state=4
case 4 : wait 1 : state=5
case 5 : green=0:orange=0: red=1
state =6
case 6 : wait 20 'seems red is always long :-)
state= 7
case 7 : red=0 :
state=1 ' again
end select
loop
now this is very simple. but we cut the logic in small pieces/states. and each state is unique. it is clear which state will be next.
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