On Tue, Dec 2, 2014 at 9:49 AM, Neil wrote: > Okay, this is an interesting option, if I understand what the intention > is. CAN is differential, but I know the MCP2551 has RX and TX pins. So > if I feed it a high or low TTL voltage, it will send the correct CANH/L > signal pair accordingly? And it will also handle bidirectional comms on > that line to send me back a high or low TTL voltage? > > I don't want to mess with firmware anymore, so really want this to be a > hardware-only change. > The thought as I was typing that was to use two pairs of wires, one for TX one for RX. And two sets of CAN transceivers. I've since re-read your first message and now realize that's a non-starter for the wire harness changes - sorry, I'll try to read better next time. It _may_ be possible to use CAN transceivers on your existing hardware... At the physical link, CAN has two states: The lines about 5v apart (Dominant, logical zero), and the lines at about the same voltage (recessive, logical 1). On the processor side of transceiver, when you put a bit on the TX line, the sender can see it on the RX line. Proper CAN engines use this for several things including error detection and bus arbitration. Without a proper CAN protocol engine, I could imagine several ways to use this link- but there would be new firmware of some type to manage collisions. So that quickly falls outside of your "want" list. -Denny --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .