Using external SPI ADC on nRF5340

[sssergsss]

Hi, 

I need close to 1Msps rates for my application and am planning on using a ADS7887 SPI ADC from TI.  My question is on how to drive the SPIM and if an example exists to do this.

These SPI ADCs start the 16 bit collection on a lower going chip select.  I assume that the way to collect data is to configure EasyDMA to collect two bytes and to have a timer drive the SPI task at a rate of approx 1Msps?  So I would have to collect to start the SPI task, collect two bytes, restart the tast etc.

Or is there some way to configure the SPIM for this specific purpose where the chip select could be driven automatically so I can simply say collect 10K samples and the processor would handle the SPI CS signaling? 

Thanks

[sssergsss]

Hi Einar, 

The ADC collects 16 bits on per CS period, kicked off by a falling edge CS. 

There is a 10nS setups time from CSlow to SCLKlow. 

The CS signal must stay high a min of 40nS after 16 SCLKs 

See the image below. 

We want to get as close to 1Msps as possible.  I want to collect 5K data samples.  

The idea is to drive CS (start of SPI task) with a timer and I believe use EasyDMA ist functions.  

Thanks for your help, 

Sergio

[Einar Thorsrud]

Hi Sergio,

I see. Then this should be possible the way you describe. You need to use array list. Then use a timer to control CS via PPI and GPIOTE and also to trigger the START task. You probably want to use a separate CC register for this as the START task needs to be triggered a little later depending on what timing you need. Then also reset the timer on this. This way there will be no CPU intervention needed while sampling the whole set of sample, only for setting it up (and for any subsequent processing).

[Natael]

Hi guys, 

I would like to ask you if in nRF5340 works the ADC.

I have been trying to configure It but It fails on:

ADC= device_get_binding ("ADC");

I have also chances the .prog file and the overlay but the error keeps going

Any sugesttion?

Best regards

[Einar Thorsrud]

Hi,

There are drivers in nRF Connect SDK for the SAADC peripheral. Please make a new question for that though, as it is not related to the topic of this thread (using an external ADC via SPI)