Hach 9186, Instrument Manual

Page: 40 / 52

40
Modbus Communication
8.3.1 Read Input Registers—Function Code 03
This command reads the binary contents of a holding register in the 4xxxx
address range. The query message specifies the starting register and quantity of
registers to be read. Registers are addressed starting at zero.
Table 13 is an
example that requests the value from register 40001.
Assume that register 40001 contains the value 5 (see Table 14 ).
8.4 Write Input Register—Function Code 06
This command writes the binary contents of a single holding register in the 4xxxx
address range. The query message specifies the register address and value to be
written. Registers are addressed starting at zero. The following message writes
the value 5 to register 40004 (see
Table 15 ). Table 16 shows the response.
Table 13 Read Input Register Query
Field Name Hex Value
Slave address 01
Function 03
Starting address high byte 00
Starting address low byte 01
Number of registers high byte 00
Number of registers low byte 01
CRC high byte 84
CRC low byte 0A
Table 14 Read Input Register Response
Field Name Hex Value
Slave address 01
Function 03
Byte count 02
Data high byte (register 40001) 00
Data low byte (register 40001) 05
CRC high byte 78
CRC low byte 47
Table 15 Write Input Register Query
Field Name Hex Value
Slave address 01
Function 06
Starting address high byte 00
Starting address low byte 03
Data high byte 00
Data low byte 05
CRC high byte B9
CRC low byte C9