Readout Examples
Readout Example of a Modbus Register
The table below shows how to read the RMS current on phase 1 (I1) in registers 32028 and 32029 (coded in FLOAT32).
-
The address of register 32028 equals 32028 - 1 = 32027 = 0x7D1B.
-
The Modbus address of the Modbus slave is 255 = 0xFF.
Request from the Master |
Response from the Slave |
||
---|---|---|---|
Field Name |
Example |
Field Name |
Example |
Modbus slave address |
0xFF |
Modbus slave address |
0xFF |
Function code |
0x03 |
Function code |
0x03 |
Address of first register to be read (MSB) |
0x7D |
Data length in bytes |
0x04 |
Address of first register to be read (LSB) |
0x1B |
Value read at address 0x7D1B (register 32028) (MSB) |
0x44 |
Number of registers (MSB) |
0x00 |
Value read at address 0x7D1B (register 32028) (LSB) |
0x0A |
Number of registers (LSB) |
0x02 |
Value read at address 0x7D1C (register 32029) (MSB) |
0xC0 |
CRC (MSB) |
0xXX |
Value read at address 0x7D1C (register 32029) (LSB) |
0x00 |
CRC (LSB) |
0xXX |
CRC (MSB) |
0xXX |
- |
- |
CRC (LSB) |
0xXX |
The converted value of the FLOAT32 registers 32028 and 32029 is 555.
The RMS current on phase 1 (I1) is thus 555 A.
Readout Example of the Table of Standard Dataset Common Registers
Since there are more than 125 registers in the standard dataset, at least three Modbus read requests are needed to read the entire table.
Request to read registers 32000 to 32123:
-
The address of register 32000 is 0x7CFF.
-
The length is 124 registers = 0x7C.
-
The number of bytes is 124 x 2 = 248 bytes = 0xF8.
-
The Modbus address of the slave is 255 = 0xFF.
Request to read registers 32124 to 32241:
-
The address of register 32124 is 0x7D7B.
-
The length is 118 registers = 0x76.
-
The number of bytes is 118 x 2 = 236 bytes = 0xEC.
-
The Modbus address of the slave is 255 = 0xFF.
Request to read registers 32340 to 32435:
-
The address of register 32340 is 0x7E53.
-
The length is 96 registers = 0x60.
-
The number of bytes is 2 x 96 = 192 bytes = 0xC0.
-
The Modbus address of the slave is 255 = 0xFF.
Request from the Master |
Response from the Slave |
||
---|---|---|---|
Field Name |
Example |
Field Name |
Example |
Modbus slave address |
0xFF |
Modbus slave address |
0xFF |
Function code |
0x03 |
Function code |
0x03 |
Address of the first register to be read (MSB) |
0x7C |
Data length in bytes |
0x8F |
Address of the first register to be read (LSB) |
0xFF |
Value of register 32000 (MSB) |
0xXX |
Number of registers (MSB) |
0x00 |
Value of register 32000 (LSB) |
0xXX |
Number of registers (LSB) |
0x7C |
Value of register 32001 (MSB) |
0xXX |
CRC (MSB) |
0xXX |
Value of register 32001 (LSB) |
0xXX |
CRC (LSB) |
0xXX |
– |
0xXX |
– |
– |
– |
0xXX |
– |
– |
Value of register 32123 (MSB) |
0xXX |
– |
– |
Value of register 32123 (LSB) |
0xXX |
– |
– |
CRC (MSB) |
0xXX |
– |
– |
CRC (LSB) |
0xXX |