Reply To: Optical dissolved oxygen solutions?

You should be using the same modbus address that you use when connected to the computer.

Looking at the datasheet again, I told you the wrong connections.  I’m sorry.  Only Y/Z are available in half-duplex mode, not A/B.  So you need to move A->Y and B->Z.  Turn off the Y/Z termination dip switch (I think).  I also told you the wrong pins for DE/REnot.  They should be A5/A6 *not* A4/A5.

If fixing the wrong connections I told you to use doesn’t fix things, try disconnecting A5 and A6 and manually setting them at the start of your program.  Set DEREPin = -1; Then in your setup function, add this:


pinMode(A5, OUTPUT);
digitalWrite(A5, LOW);
pinMode(A6, OUTPUT);
digitalWrite(A6, HIGH);


Since it is a fully duplex chip, both the receiver and driver can be enabled at the same time, unlike half-duplex chips like the MAX485.