We´re working to set up Communication with an external unit, that talks MODBUS RTU over RS485. We have a number of parameters that we´d like to read, and two that we would need to write to the unit.
The OEM supplier mentions the following
Read data instruction (0x03)
Requirement :
Node address (1 byte)
Function code : 0x03
Start address (2 byte) : 0000 - FFFF
Data amount (2 byte) : 1 ~ 125
Check digit (2 byte) CRC check
Answer
Node address (1 byte)
Function code : 0x03
The number of bytes (1 byte) - N = data amount * 2
The data content (N byte) - each data 2 bytes, the high data in the first, low data after
Check digit (2 byte) CRC check
Write data instruction (0x10)
Requirement
Node address (1 byte)
Function code : 0x10
Start address (2 byte) : 0000 - FFFF
Data amount (2 byte) : 1 ~ 120
Byte number (1 byte) n = data amount * 2
Data content (n byte)
Check digit (2 byte) CRC check
Answer
Node address (1 byte)
Function code : 0x10
Start address (2 byte) - 0000 - FFFF
The data amount (2 byte)
Check digit (2 byte) CRC check
– so, now to the problem - how do we actually set it up?
so, one parameter is for example called “Return Oil Temp”
In the OEM manual it is described as
Register address : 42012
Type : Read
Type of data : 16 bit signed binary
how do I actually generate the Query, and where is the value returned? i´ve tried lots of different ways, and dont get any data.
thanks in advance for any help!