I am reading an 8 byte modbus parameters and it seems to be returning the least significant byte as a zero. Has anyone else had this issue?
Problem with reading 8 byte unsigned modbus data
It's only zero'ing a byte, not a register? Here's the code that would be doing the transformation from the byte array over the wire to a number for the consumer: https://github.com/infiniteautomation/modbus4j/blob/master/Modbus4J/src/com/serotonin/modbus4j/locator/NumericLocator.java
If you actually mean the register (two bytes) then I would wonder if you documentation is 1-indexed and your offsets need to be shifted by 1 as Mango is 0-indexed.
If you do indeed mean a single byte, then I wonder if that was something bizarre with the device.
If I simply read the registers from the device, I get back what I expect. If I split the read into two 4 byte unsigned reads, then the data is correct in each part. I actually wrote the device code and am sure it works as intended.
One more question: Is it possible to access the actual array of bytes read from the device if the point data is set to a fixed length string?
This would really simplify my script processing of special data types.
Hmm. Well, I'll think about it more but I'm fairly confident Modbus4J handles it properly.
Yeah you should be able to unpack the string the same way you packed it.
Edit: My recommendation, to prove what you're saying, would be to disable all the points on your modbus data source, the enable IO logging and the two points as 4 byte variants. Do the read, disable the points. Enable the 8 byte single point, do a read. Post the resultant IO log.