Start of ref block within a rule.

If present, the REF field must be declared as the first field within the Rule. Failure to do so results in an error being reported in compilation.

The REF field of each RULE typically sets, via the sref variable, the value that will be sent as a reference to the drives of the axis(s) involved (use tref in case of speed loop closure on axis control).

If no value is assigned to the axis sref in the REF field, the value used as a reference will be that of the previous sampling (similar behavior will occur in case of tref assignment).

The value assigned to the sref variables can be the result of any expression: it will still be made integer and limited within the range of action of the reference emission device configured in the RTE.CFG file (similar behavior will occur in case of tref assignment).

If the sr_ovf_m alarm is enabled for the axis there will be the output of that alarm whenever, at runtime, the value assigned to the sref variable is outside the variation range mentioned above (similar behavior will occur in the case of tref assignment and tr_ovf_m alarm enabled).

Any assignment of a value to the sref or tref variables outside the REF field is considered an error by the compiler.

NOTE: May be omitted.