42
isoMIL425_D00203_03_M_XXEN/03.2019
7. Data access using the Modbus RTU protocol
Requests to the ISOMETER® can be made using the function code 0x03 (read
multiple registers) or the command 0x10 (write multiple registers). The
ISOMETER® generates a function-related answer and sends it back.
7.1
Reading out the Modbus register from the ISOMETER®
The required Words of the process image can be read out from the ISOMETER®
"holding registers" using the function code 0x03. For this purpose, the start
address and the number of the registers to be read out have to be entered.Up
to 125 Words (0x7D) can be read out by one single request.
7.1.1
Command of the master to the
ISOMETER®
In the following example, the ISOMETER® master requests the content of the
register 1003 with the address 3. The register contains the channel description
of measuring channel 1.
Byte Name
Example
Byte 0
ISOMETER® Modbus address
0x03
Byte 1
Function code
0x03
Byte 2, 3
Start address
0x03EB
Byte 4, 5
Number of registers
0x0001
Byte 6, 7
CRC16 Checksum
0xF598
