Yes you are correct I am driving it directly from the PIC output pin. I was familiar with terminating with the characteristic impedance of the cable for RS485 (differential) but I wasn't sure if that was also the case for RS232 (single ended). I hadn't seen a reference to that. I guess empirical testing is in order.

You're right the 100 ohm termination would overload the output pin, I hadn't really considered the over all circuit loads yet and was just throwing numbers down, my bad. I appreciate the reminder though.

RS485 is in the future but I'm just trying to add this to a board I've already made. I'll redesign the board with an RS-485 chip, but until then ......

Mark