I’m trying to understand the J1850 functionality. What exactly does the signal J1850_PWM_nVPW do?
If I understand correctly, it selects if LM317T should output either 5.76 or 7.7V, but what does that do for the J1850? Are there different signal levels on different cars? Or something else?
Welcome to the forum.
I remember there have been a couple of discussions on J1850. Check this one out:
Someone in this thread might have an answer for you.
There is a library for the VPW communications. But it needs a lot of work. It is listed in that thread and I have it up on my github. If you run it, it will print out whatever it receives on the port and does allow you to type stuff but it is a very rough program otherwise. If you look through the code it should show what it is doing. There is documentation online for it as well in the library.
If I recall it seems like there is an enable pin for J1850 and a pin that determines if it will be VPW or PWM. But that information should be in the thread that Mr Sharpe posted.