13.3 Read input registers, 0x04
This function is used for reading input registers from the slave. Input
registers are read-only registers by definition. The request telegram
specifies the starting address, that is the address of the first register
to be read, and the number of holding registers to read. In the
telegram, register addresses start from zero, meaning that registers
numbered 0-16 are addressed as 0-15.
Example of request from master to slave
Field Value
Address 0x01
Function code 0x04
Start address HI 0x10
Start address LO 0x10
Quantity HI 0x00
Quantity LO 0x03
In the request, the slave with address 1 is asked to deliver three
contiguous registers starting from address 0x1010: 4112, meaning
register 4113.
Example of response from slave to master
Field Value
Address 0x01
Function code 0x04
Byte count 0x06
Register 4113 HI 0x22
Register 4113 LO 0x22
Register 4114 HI 0x22
Register 4114 LO 0x22
Register 4115 HI 0x22
Register 4115 LO 0x22
In the response, the byte count is six since there are three registers
of two bytes. All three registers hold the value of 0x2222.
13.4 Write single register, 0x06
This function is used for writing a single holding register in the
slave. The request telegram specifies the address of the register
that is to be written. Register addresses start from zero, meaning
that a register numbered 10 is addressed as 9.
The normal response is an echo of the request, indicating that the
value was written.
Example of request from master to slave
Field Value
Address 0x01
Function code 0x06
Address HI 0x10
Address LO 0x00
Value HI 0xAF
Value LO 0xFE
In the request, the slave with address 1 is asked to write the value
of 0xAFFE to the register at address 0x1000.
Example of response from slave to master
Field Value
Address 0x01
Function code 0x06
Address HI 0x10
Address LO 0x00
Value HI 0xAF
Value LO 0xFE
The response is an echo of the request.
13.5 Write multiple registers, 0x10
This function is used for writing a block of contiguous holding
registers in the slave. Register addresses start from zero, meaning
that a register numbered 100 is addressed as 99.
Example of request from master to slave
Field
Value
Address 0x01
Function code 0x10
Start address HI 0x00
Start address LO 0x20
Quantity HI 0x00
Quantity LO 0x02
Byte count 0x04
Register 33 HI 0x00
Register 33 LO 0x01
Register 34 HI 0xB0
Register 34 LO 0xB0
In the request, the slave with address 1 is asked to write the value
of 0x0001 to the register at address 0x0020 and the value of
0xB0B0 to the register at address 0x0021.
Example of response from slave to master
Field
Value
Address 0x01
Function code 0x10
Start address HI 0x00
Start address LO 0x20
Quantity written HI 0x00
Quantity written LO 0x02
The response returns the function code, starting address and
quantity of registers written.
38
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