I haven’t thought about using parity. That could be something to look into. I think I found a potential cause of my issue however.
I checked my line for shorts and there are none, so that’s a good thing. I powered the RS232 connector with a 5 volt source at the VCC and GND instead of drawing 3.3v power from the photon. I think my RS232 to TTL needed to use 5v logic. Here is the link to it if you’re interested in confirming that for me. This really helped! Now, both my datalogger and my photon serial outputs show the same thing consistently.
My datalogger shows this:
RX: 01 03 00 01 00 08 15 CC
TX: 01 83 02 C0 F1
And Photon shows this:
TX: 1 3 0 1 0 8 15 CC
RX: 1 83 2 C0 F1
And that gives me an error 0x02 which is a Modbus protocol illegal data address exception. So perhaps my datalogger is not receiving the correct format of numbers to read registers? Could this be why it’s generating the “00’s” in front of the “01” and “08”?