AM623: How to connect the ADS981x to the AM62x ?

Hi Ito-san,

my below response is assuming you are planning to use Linux in some capacity.

So I had a look at that ADC you mentioned, it is not really suitable for direct and easy interface with a Linux MPU. It is a high performance / high throughput ADC, which is why it provides a parallel output interface to efficiently offload its data. Just using a single standard SPI interface and a couple of GPIOs won't work. If you look at it closer it is designed to be used in conjunction with FPGAs really.

This being said, you could still make it work with AM62x, if you offload the interface handling to another core, specifically the PRUSS. The PRUSS peripheral is perfect for low-level low-latency bit-bang type of I/O operations, so you could write a program that runs on PRUSS to interface directly with the external ADC to fetch the data and store it in device memory. We do not have example code that specifically does what you need so you would need to develop your own software based on our general PRUSS examples and IPC examples. But I don't see why this couldn't be done with the right software implementation.

Another option is to re-consider which ADC to use. If the goal is to use Linux I'd look for an ADC that already is supported by existing Linux drivers so you can eliminate or at least minimize any custom development effort.

Regards, Andreas

There are some application notes about high speed interface implementation by PRU:

https://www.ti.com/lit/an/sprade1/sprade1.pdf

https://www.ti.com/lit/ug/tidua38a/tidua38a.pdf

https://www.ti.com/tool/ADC-PHI-PRU-EVM

And there are PRU-ADC examples in AM335x Linux SDK:

tony@ubuntu22:~/ti-processor-sdk-linux-am335x-evm-07.03.00.005/example-applications/pru-adc-1.0$ ions/pru-adc-1.0$ 

Tony Tang said:

There are some application notes about high speed interface implementation by PRU:

Tony, thank you so much for chiming in here!! I admit I was not readily aware of these app notes, so I'm glad you added those links here!

Regards, Andreas

Andreas and Tony, thanks for your help.

Additional questions.

・What sampling rate would allow me to connect via normal SPI or GPIO?
I found an example of a 12-bit 1.68 Msps MSPM0 ADC connected via SPI.

MSPM0 – ADC Attach on AM62x using SPI

・If the ADS981x is controlled by a PRU, is the I/F GPIO?
・Is it possible to connect the ADS981x with QSPI?
・ What ADCs do you recommend to connect to the AM62x?

Best regards,

Ito

I'm out on PTO this week but will look at this again next week.

If you want a recommendation for an ADC you should provide some context about the signal(s) you are trying to measure.

Regards, Andreas

Hi Andreas,

Thank you for your help.

I don't have any signal data yet.

Best regards,

Ito

K.Z said:

I don't have any signal data yet.

If you don't know what signal to measure, how can you pick an ADC?

You'd want to figure out your signal bandwidth, the input voltage range, the resolution you want to measure/sample it, the desired conversion speed, etc.

Regards, Andreas

Hi  Andreas,

Customers would like the following features.

Resolution: 18 bits or more
Sampling rate: 1 MSPS or more.
Channels: 4 or more

Best Regards,

Ito

Hi Ito-san,

ok that's a starting point, thanks. I'm on PTO this week but I'll look at this again more closely next week to see what can be recommended here.

Regards, Andreas

Hi Andreas,

Have you found an ADC to recommend?

Best Regards,

Ito