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Third SPI?

Topic last updated 04 Oct 2012, by Stephen Paulger. 2 replies
James Bennett
04 Oct 2012

Hello,

I'm trying to connect three SPI devices at once on the same MBED and I was wondering if this is possible?

Thanks, James

Martin Smith
04 Oct 2012

Yes this is fine, just use different chip select lines for each device.

Stephen Paulger
04 Oct 2012

James,

There are two SPI interfaces on the mbed but you can connect multiple devices to each one. For example you could connect three SPI devices as shown below.

/media/uploads/stevep/20121004_163449.jpg

Pins 5,6 & 7 are the one of the mbed's SPI interfaces and are shared with all 3 devices. Each SPI device has it's own CS (chip select) line (8, 9 & 10) which you would set low to select the device. You can see an example of a single SPI device being selected and deselected on the SPI handbook page.

You might also choose to connect one of your SPI devices to one SPI interface and 2 to the other.

Steve