Bender ISOMETER isoHV525, Руководство пользователя

Страница: 31 / 52

31 isoHV525_D00297_04_M_XXEN/05.2018
7. Data access to the isoHV525-S4-4 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 the Modbus register from the ISOMETER®
The required Words of the process image can be read from the "Holding registers" of
the ISOMETER® using the function code 0x03. For this purpose, the start address and the
number of the registers to be read have to be entered. Up to 125 Words (0x7D) can be
read with one single request.
7.1.1 Master device sends a command to the ISOMETER®
In the following example, the ISOMETER® master requests the content of register 1003
with address 3. The register contains the channel description of measuring channel 1.
7.1.2 The ISOMETER®s answers the Master
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
Byte Name Example
Byte 0 ISOMETER® Modbus address 0x03
Byte 1 Function code 0x03
Byte 2 Number of data bytes 0x02
Byte 3, 4 Data 0x0047
Byte 7, 8 CRC16 Checksum 0x81B6