Troubleshooting Expressions

The Expression Editor displays the Assignment Expression in black text if it is valid, and in red text when it is invalid. Listed below are common errors in the assignment expression syntax:

Mixed Data Types:

Data types cannot be mixed in the assignment expression without explicitly converting them. A number thatdoes notcontain a decimal point is considered to be a DINT data type. A number thatdoescontain a decimal point is considered to be a REAL data type.

Example1:

Assume MyVariable is defined to be a REAL type. The following expression is not valid, because "3" is a DINT type:

MyVariable:=_Axis[0].ActPos+3

The following expression is valid because "3.0" is a REAL type:

MyVariable:=_Axis[0].ActPos+3.0

The following expression is valid because the DINT_TO_REAL() function converts "3" to a REAL type:

MyVariable:=_Axis[0].ActPos+DINT_TO_REAL(3)

Example2:

Assume MyVariable is defined to be a DINT type. The REAL_TO DINT() function converts the REAL type part of the expression to a DINT. The following expression is not valid because "2" is a DINT type and _Axis[0].ActPos is a REAL type:

MyVariable:=REAL_TO_DINT(Abs(_Axis[0].ActPos/2))

The following expression is valid because "2.0" is a REAL type and _Axis[0].ActPos is also:

MyVariable:=REAL_TO_DINT(Abs(_Axis[0].ActPos/2.0))

Similarly, the following expression is not valid because the Abs() function returns the data type of its arguments, which in this case is REAL, while MyVariable is a DINT type:

MyVariable:=Abs(_Axis[0].ActPos/2.0)

Illegal Expression Order

An expression in the Expression (113) command must begin with "[tag]:= ", where tag is any register in the RMC and may be given as a register address, tag name, or variable name. See the Assignment Expression topic for details.

Inaccurate Results

If the results of some expressions are not precisely correct, it may be caused by truncation due to the 32-bit limit of RMC data.