Introduction.

Workshop PG5 Exercise Chapter 7
In the case of a counter, the LoaD instruction depends on the state of the
ACCU. As we want this load to be an unconditional one, we have to be sure
the ACCU is H. So set the ACCU to H first.
XOB 16
; Code executed at start up
ACC H
; Load the counter with
LD NumberOfFreeSlots ; the value 8 ( unconditionally )
8
EXOB
; end of start-up program
5. We then simply decrement the counter 100 each time a car enters the lot and
increment the counter as soon as one leaves the lot.
Each time we have a rising edge on the input 0 ( Sensor at the parking lot entrance
) we want to decrement the counter “NumberOfFreeSlots”:
STH NewCar_Signal
DYN DynamiseNewCar
DEC NumberOfFreeSlots
The DYN instruction memorises the state of the Input 0 in a flag (Dynamise-
NewCar)from one program cycle to the next. The ACCU is then set as soon as
the DYN instruction sees that the Input 0 has gone from 0 to 1.
The DECrement instruction is only executed, if the ACCU is set. Do the same
thing for the parking lot
Exit.
STH Car_leaving_Signal
DYN DynamiseCar_leaving
INC NumberOfFreeSlots
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