Modbus TCP
A-2
AC30V series Variable Speed Drive
Fixed Parameter Mapping
Each parameter number is mapped onto
two
consecutive Modbus registers regardless of the parameter data type. The relationship between the
Holding 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. the
register 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 AC30V 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 - ARRAYS
Some parameters have multiple elements and are classified as parameter arrays. A parameter array has a parameter number that represents
the
whole
of the array, but also has parameter numbers that represent each
element
of the array. An example is given below.
Array Example
A parameter array called
Recent Trips
has 10 elements.
Parameter Number Parameter – Recent Trips
895
Whole array
896
index 0
897
index 1
905
index 9
If 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 parameter
number 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
Accessing the parameter arrays via the parameter number that represents the whole array is not recommended. This will access only the first
four bytes (2 registers) of the array. The array should rather be accessed via its elements.
