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Project Help and Ideas » Multiple slaves on SPI connection

October 17, 2011
by claesz
claesz's Avatar

Hi again guys. Need some advice than I am sure is basic knowledge but perhaps you can point me in the right direction.

How would I go about connecting to multiple devices through SPI? All SPI communication defaults to PB2-5 on the 328p. Could I use another port, like any PC port, for slave selection, or would I time communication so that I first communicate with S1, then S2 etc. I found some posts touching on this on this forum, but a lot of it went woosh over my head. Any practical examples or code sniplets would be greatly appreciated.

October 18, 2011
by hevans
(NerdKits Staff)

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Hi claesz,

You would need one pin to select every slave you want to listen to that particular byte you are about to send across. In fact when a chip is a master, the SS pin is treated just like a normal digital output pin.

Humberto

October 18, 2011
by claesz
claesz's Avatar

Hi Humberto,

Thanks for your reply. So even if the 328p has only one dedicated SS pin, I could use any digital output pin on the master for the slave select?

As I understand SPI it relies on synchronized communication between master and slave. Can you still use a shift register to hook up more than one slave or would that create timing problems on communication?

October 18, 2011
by claesz
claesz's Avatar

Actually I think I found that the answer is "yes" you can use any digital pin as SS pin. It seems to have been discussed here:

http://www.nerdkits.com/forum/thread/1551/

My apologies.

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