how many I2c and SPI device can be connected in nRF51822 device

[Rajeshmcy]

This is Rajesh.C working for Sienna ECAD-Bangalore, India. We are using nRF51822 BLE in our design. I would like to know how many I2C and SPI device can be connected to the nRF51822. Currently in our design we have interfaced two SPI and three I2C devices.
Kindly suggest whether we can go ahead.

Thanks and regards Rajesh.C

[John]

Hi Rajesh,

Two SPI and 3 I2C seem like reasonable numbers to me.

On the I2C you are theoretically limited to the number of devices that can be addressed by the master (I am assuming your nRF51822 is master). I believe this is 127. However, what you will really be limited by is how many addresses can be set on your slave devices. You would have to examine their data sheets to determine that.

On SPI I think you will be limited by the number of chip selects you can control.

Regards, John

[ovrebekk]

John is correct. The upper limit for I2C is 127, and for SPI it is limited by the number of chip select lines you have.

In practice you also have to take into account that for every device you add to the bus the capacitance of the bus lines will increase, which could limit the speed of the bus.

For 2-3 devices I don't expect this to be an issue, but it depends on your hardware, and the speeds at which you are trying to run the interfaces.