I've have a couple instruments that use modbus communication; I've figured out how to format and send commands to the devices, but I can't figure out how to convert the response. It seems like it should be pretty simple: the device sends a response in hex, I've dissected the hex to get the response from two registers; the manual states: "Sensor and process values are stored as big-endian, 32-bit IEEE-754 floating point numbers spanning two registers. Your control system will need to concatenate these into a single value to interpret them correctly." I'm not sure if I'm running into an endian issue or something else. I disabled the main part of the code and have a dummy code to mimic a response I received from the device. I'm pulling a temperature measurement for these values and I'm expecting something around 26 (Celsius). I've also attached the manual but I don't find it very helpful.

@altenbach wrote: OK, you have a SGL, not a DBL and all you need to do is concatenate the two registers in the right order and unflatten the 4byte string to a SGL using the correct byte order (big endian, according to the manual). (I cannot really tell if you are reading the right registers.) Yeah, I was working through the same thing. I'm fairly convinced we have incorrect data based on the result the OP is looking for.

LabVIEW

hex conversion + endian

Solved!

Author

Thanks all! So there was an issue in the read command; I needed to send the listed register in the manual - 1, (so 1204, instead of 1205).

Message 11 of 11

(403 Views)

LabVIEW

hex conversion + endian

Re: hex conversion + endian