DOCA0091EN-08

### 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

0xFF

0xFF

Function code

0x03

Function code

0x03

0x7D

Data length in bytes

0x04

0x1B

0x44

Number of registers (MSB)

0x00

0x0A

Number of registers (LSB)

0x02

0xC0

CRC (MSB)

0xXX

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

0xFF

0xFF

Function code

0x03

Function code

0x03

0x7C

Data length in bytes

0x8F

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