Remove RETAIN qualifier for F_TRIG and R_TRIG 'M' variable. This is not following standard, and implicitely consumes a lot of RETAIN memory. User can explicitely qualify R_TRIG of F_TRIG instance as RETAIN if needed.
FUNCTION WEIGH : WORD (* BCD encoded *)
VAR_INPUT (* "EN" input is used to indicate "scale ready" *)
weigh_command : BOOL;
gross_weight : WORD ; (* BCD encoded *)
tare_weight : INT ;
END_VAR
(* Function Body *)
IF weigh_command THEN
WEIGH := INT_TO_BCD (BCD_TO_INT(gross_weight) - tare_weight);
END_IF ;
END_FUNCTION (* Implicit "ENO" *)