Page 381 - Gas Detection Systems Training Manual

The normal response is an echo of the query header (which contains the unit number, function code, starting address and number of registers).
Query
The query message specifies the register reference to be preset. Registers are addressed starting at zero: register 1 is addressed as 0.
Here is an example of a request to write holding registers 42119 - 42121 to set the low alarm set point floats 400.12 (43C8 0F5C Hex) in slave device 17, for sensor 1:
Write Multiple Holding Registers Query
Field Name
Slave Address Function Code Address High Address Low
Item Count High Item Count Low Num Data Bytes Data High (42119) Data Low (42119) Data High (42120) Data Low (42120) Data High (42121) Data Low (42121) CRC Low Byte CRC High Byte
Example (Hex)
11 10 08 46 00 03 06 42 59 43 C8 0F 5C 92 27
The normal response is an echo of the query header, returned after the register contents have been written.
SEC 3120 16-bit Modbus Manual Page 41 Of 46 Sensor Electronics Corporation For Version 1.2 and above December 2012 P/N 1580282, Rev. 1, 20121228