>There are several approaches to this. As others have mentioned RC
>oscillators are not usually stable enough for async serial, but
>there are plenty of clocked protocols hat are workable with RC
>oscillators. But here's the problem - an 8Mhz PIC is chugging along
>at 2 MIPS. 2 million/64k leaves about 31 instructions per bit time.
>Probably not enough to do anything else useful. Find a way to
>reduce your data needs or get a bigger proccessor.

rather than use an async or SPI/I2C type interface, is the interface that TI
used for their calculators. uses two pins on each device, is bi-directional,
is self clocking, doesn't depend on processor speeds (faster unit works at
slower processor pace) and can generally be done as a non-interrupt task.
See http://www.ticalc.org/pub/text/calcinfo/link86all.zip and
http://www.ticalc.org/pub/text/calcinfo/ti-prot.zip also has some hardware
info.

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist