> Regarding the RS4xx family, I find the descriptions in Wikipedia and
> elsewhere quite complicated, but would I be correct to say that the
> half-duplex, multi-master nature of RS-485 makes drivers built for it a
> better match for SPI?

RS485 drivers can be used for uni-directional balanced data transfer, 
IMHO they would be a good choice. Technically other RSxxx 
driver/receivers might be OK too, but take a typical RS485 transceiver 
and you can use the same chip at both ends. They tend to be easily 
available too. SN75176B is the jellybean chip.

I2C extenders are probably easier (only one chip at each end), but 
probably much less resistant to all kinds of interference. Whether that 
matters is up to you...

-- 

Wouter van Ooijen

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Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: www.voti.nl/hvu

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