A-2 FieldbusesAC30 series Variable Speed InverterFixed Parameter MappingEach parameter number is mapped onto two consecutive Modbus registers regardless of the parameter data type. The relationship between theHolding Register or Input Register is given as:Register number = (parameter number - 1) * 2 + 529• If the parameter has a data type that uses one byte then it will occupy the low byte of the first register and the high byte will be zero, i.e. theregister will not be sign extended.• If the parameter has a data type that uses two bytes then it will occupy the first register.• Unused register locations will read zero; writing to that location will have no effect.• The word order of 32-bit parameters is determined by the inverter parameter 0940 High Word First.• Writable 32-bit parameters will only accept a change in value if both registers mapped to the parameter are written to in the same request.Fixed Parameter Mapping - ArraysSome parameters have multiple elements and are classified as parameter arrays. A parameter array has a parameter number that representsthe whole of the array, but also has parameter numbers that represent each element of the array. An example is given below.Array ExampleA parameter array called Recent Trips has 10 elements.Parameter Number Parameter – Recent Trips895 Whole array896 index 0897 index 1905 index 9If the parameter number of the whole array is 895, then the parameter number of the element index 0 of the array will be 896, the parameternumber of the element index 1 will be 897, etc.Note: String array parameters access their elements via parameter numbers that are calculated in a different way (see Fixed Parameter Mapping- Strings).Accessing the parameter arrays via the parameter number that represents the whole array is not recommended. This will access only the firstfour bytes (2 registers) of the array. The array should rather be accessed via its elements.
