Hi,
I am using the Digi RS485 Adapters to establish a connection between a modbus sensor and a data acquisition system.
My issue is that the data that is output from the module (XBee Pro S2B) is split up such that the modbus protocol doesn’t recognise the data. Specifically, the modules always send out the first byte first before a wait, then the rest comes out at once. This occurs in both directions. I have confirmed this using an analyser and other software/hardware.
I understand that there is packetisation but I am sending data with a length of only about 10-12 bytes at a time and I have set RO to 0x0F so this should apparently not be an issue as the data is supposedly always packeted together.
I have tested the modules with/without the adapters and the result is always the same. If I wire up the sensor directly to the data acquisition system it works flawlessly.
If I manually assemble the modbus packets with a ‘throw away’ character first, I get a response from the sensor because it recognises the first byte as a different invalid message and the rest arrives in one piece. Obviously this is not a resolution because I cannot read the response because I can’t hack a ‘throw away’ byte into the response of the sensor.
My configuration consists of one AT coordinator and one AT end node. I have entered the destination addresses of each and am not using any broadcasts. I read somewhere that routers should be able to communicate but I could not get any other combinations of configurations to talk. I have tried a couple of firmware versions and I can’t seem to download the latest from my workplace so I don’t know if this is a fix in a later firmware
What am I missing?