"once" statement not working within "for" loops (PAC)

Hi,
I am iterating over a set of groups to see what their state is.
Doing them individually in is fine but when I try to use in a loop the "once" statement keeps firing as if it were a simple "if" statement.

Herer is a sample code

for Group := 1 to 10 do
begin
Format(GroupIs, 'Group ', Group, ' is ON', #13#10);
once GetCbusState(254, 56, Group) = ON then
WriteSerial(1, GroupIs);
end;

I should only see that serial routine fire once I activate the group, but it keeps firing for every module run.

Any clues? Ot if there is a better way of doing this?

 

.. scratch this .. just found it in the help file ... "don't use in a loop ..."
Any ideas on how to loop through a group and detect a change?

 

The ONCE statement works by storing the last value of the variable internally and then comparing it with the new value. Since it only stores a single value, you can't compare it with multiple different groups. The way around this is to do your own ONCE instruction using an array of the previous values

in Global Variables add:

lastValues: array[1..10] of boolean;

Code:

for Group := 1 to 10 do
  if (GetCbusState(254, 56, Group) = ON) and (lastValues[Group] <> ON) then
  begin
    lastValues[Group] := ON;
    Format(GroupIs, 'Group ', Group, ' is ON', #13#10);
    WriteSerial(1, GroupIs);
  end
  else
    lastValues[group] := OFF;

Note also you can simplify the first line to:

if (GetCbusState(254, 56, Group) and not lastValues[Group] then
etc.

because both expressions are already booleans.

 

Thanks Ashley!
I will give it a try.