Example including execution check

At a Glance

The following example illustrates the READ_VAR function with a management parameter check.

Programming the function

Programming in ST:

IF NOT %M21 AND %I0.1.2 THEN

   %MW210:4 := 0;

   %MW212 := 50;

   READ_VAR(ADDR(’0.3.1.7’),’%MW’,20,1,%MW210:4,%MW1701:1);

   SET %M21;

END_IF;

the input bit %I0.1.2 controls the function,
the internet bit %M21 is used to test the activity of the function,
%MW210:4 := 0; initializes the management table to 0,
MW212 := 50; initializes the timeout value to 5 seconds.

NOTE: READ_VAR(ADDM(‘0.3.1.7’),’%MW’,20,1,%MW210:4,%MW1701:1); syntax must be used for Modicon M340 PLCs as ADDR function cannot be used by a Modicon M340 PLC.

Programming the exchange check

Programming in ST:

IF %M21 AND NOT %M210.0 THEN

   INC %MW214;

   IF %MW211 = 0 THEN

      INC %MW215;

   ELSE

      SET %Q0.2.2;

      INC %MW216;

      %MW217 := %MW211;

   END_IF;

END_IF;

%MW214 counts the number of exchanges,
%MW215 counts the number of correct exchanges,
%MW216 counts the number of exchanges generating errors,
%MW217 stores the error message,
%Q0.2.2 indicates an exchange failure.