> I now want to put something perhaps like the FTDI245BM chip. Or a Microchip part. Or a Cypress part. Or ?
>
>Is it possible to just buy a chip solution and put it on the board such
>that I talk to it via my serial data lines so my PIC code is for the most part unaltered?

Yes, that's what I'm doing  www.mobilecommand.net
I have a 6 pin interface that carries two TTL handshake lines, and two TTL data lines, 5V power and ground to an interface card.

If I plug in the 232 card, then it's a max chip, four caps and a connector.

If I plug in the USB card, then there's a bit more stuff on the card, but it looks the same to me.  One difference, the USB card is powered from the host over the usb cable, so it doesn't eat my batteries.

The FTDI drivers create a virtual com port, and work quite well.

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