Seems like they use tx pin to switch driver direction. That way they create an open collector bus which is not EIA485 compliant, but it can work if you add biasing resistors. I would not use it this way in the field.
Thanks. Just so I am clear, are you saying that “it isn’t compliant but will most likely work as is,” or that “That probably won’t work?” I am “capable” of soldering and building my own boards, but it’s not really something I do. I’m more of a software guy. A few years ago I moved to the sticks. No longer <5 minutes from the electronics shop where I can go to replace parts. I feel even less confident now.
dmp
There are many things involved before knowing if it will work reliable. I’ve had many issues with rs485 in the field, so I folow the standard to the last letter 
Cable length, cable type, baudrate, slew rate, environmental noise, terminating resistors, stub length, number of nodes, shielding, etc.
BTW: In 30 minutes it should be possible to solder a 8pin IC, some resistors and a decoupling capacitor on a prototyping board.
Thank you very much for the info!
dmp