Nidec H300 - Extended Data Types

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HVAC Drive H300 179
Issue Number: 3
10.3.7 Extended data types
Standard MODBUS registers are 16bit and the standard mapping maps a single Pr xx.yyy (e.g.Pr 01.021) to a single MODBUS register. To support
32 bit data types (integer and float) the MODBUS multiple read and write services are used to transfer a contiguous array of 16bit registers.
Slave devices typically contain a mixed set of 16 bit and 32 bit registers. To permit the master to select the desired 16 bit or 32 bit access the top two
bits of the register address are used to indicate the selected data type.
The selection is applied for the whole block access.
The 2bit type field selects the data type according to the table below:
If a 32 bit data type is selected then the slave uses two consecutive 16 bit MODBUS registers (in 'big endian'). The master must also set the correct
'number of 16 bit registers'.
Example, read Pr 20.021 through Pr 20.024 as 32 bit parameters using FC03 from node 8:
Table 10-17 Master request
Table 10-18 Slave response
NOTE
Type field
bits 15-14
Selected data type Comments
00 INT16 backward compatible
01 INT32 -
10 Float32 Not supported
11 Reserved -
Byte Value (Hex) Description
0 0x08 Slave destination node address
1 0x03 FC03 multiple read
20x47
Start register address Pr 20.021
(16384 + 2021 - 1) = 18404 = 0x47E4
30xE4
40x00
Number of 16bit registers to read
Pr 20.021 through Pr 20.024 is 4x32 bit registers = 8x16 bit registers
50x08
6 CRC LSB CRC
7 CRC MSB CRC
Byte Value (Hex) Description
0 0x08 Slave destination node address
1 0x03 FC03 multiple read
2 0x10 Length of data (bytes) = 4x32 bit registers = 16 bytes
3-6 - Pr 20.021 data
7-10 - Pr 20.022 data
11-14 - Pr 20.023 data
15-18 - Pr 20.024 data
19 CRC LSB CRC
20 CRC MSB CRC
bit 15
TYP1
bits 0 - 13
Type select Parameter address
X x 100+Y-1
bit 14
TYP0