>I was thinking of the concept of using ethernet, which will
>INSTANTLY solve my problems! Each PIC would have an IP address
>and be connected by ethernet. But those solutions require
>purchase of a device similar to the Xport which is in the
>order of $50.

Not necessarily. Look at the protocol in the document of this link.
http://www.digitrax.com/loco1hdr.htm and download the PDF file from the link
at the bottom. This implements something similar to what you suggest above.
The hardware required at the PC end can be pretty minimal. I have not linked
direct to the PDF as it is a proprietary protocol, and you should read the
conditions of use before downloading, but it will give you an idea of how to
go about it on an ordinary serial line.

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