EECS20N: Signals and Systems

Parking Meter Example

States = {0, 1, 2, ..., 60}

Inputs = {coin5, coin25, tick, absent}

Outputs = { expired, safe, absent }

initialState = 0

where safe simply indicates that there is still money in the meter. The update function is given by the following table:

 

if
then update(s, x) =
x = tick and (s = 0 or s = 1) (0, expired)
x = tick and s > 1 (s - 1, safe)
x = coin5 (min(s + 5, 60), safe )
x = coin25 (min(s + 25, 60), safe )
x = absent (s, absent)

 

Example:

InputSequence = coin25, tick 20, coin5, tick 10, ...

StateResponse = 0, 25, 24, ..., 6, 5, 10, 9, 8, ..., 2, 1, 0 5

OutputSequence = expired, safe, safe, ..., safe, safe, safe, safe, safe, ..., safe, safe, expired 5