Data Coercion

The Modbus RTU Slave Interface performs run-time coercion for all data types.

Discrete data types are coerced according to the following guidelines.

Memory Type

Data Source

Source Value

Target Value

0X

CIMPLICITY

zero (0)

0

 

CIMPLICITY

non-zero (!= 0)

 

Modbus master

0

 

Modbus master

0xFF or 0x01 (depends on function code)

1X

CIMPLICITY

zero (0)

0

 

CIMPLICITY

non-zero (!= 0)

 Guidelines. Analog data types are coerced according to the following guidelines.

  1. For analog points with engineering units, the Modbus RTU Slave Interface will use the engineering unit value when converting to/from Modbus data values.

  2. For analog points without engineering units, the Modbus RTU Slave Interface will transfer the raw value.

  3. CIMPLICITY point values will be coerced to two byte unsigned integer values. Thus, the fractional portion of real values will be lost.

  4. The Modbus RTU Slave Interface will reject any CIMPLICITY point value outside of the range defined by the Modbus Register Limits. .

More information

Expected Modbus RTU Slave runtime behavior.