[sdiy] SPI comms - how fast is reasonable?

[Neil Johnson]

Hi Tom,

> Has anyone tried communicating with multiple voice cards using SPI?  
> (silly question - someone is bound to have done this). This is where  
> I'm going with this. I'm dealing with selecting different voices in  
> software, rather than using any slave selects or such like. This  
> technique has the downside that all messages go to all voices, so the  
> voices finish up dealing with a fair number of irrelevant (to them)  
> messages. But it saves IO pins.

As we discussed on gyruss last year a better solution is to use 9-bit asynchronous messaging with RS485 multidrop.  The dsPIC UARTs support 9-bit address mode operation, and this will cut down your interrupt handling on all the slaves - all slaves only get interrupted on address bytes, and then only on the data bytes for messages they want to receive.

And optionally RS485 to help with signal integrity and noise reduction.

Cheers,
Neil
--
http://www.njohnson.co.uk