ADS1299EEGFE-PDK: Stuck at reading registers with Arduino Uno

Hello Tim,

Thank you for your post. Can you confirm whether the nDRDY pin is toggling at the default data rate after your start-up routine is completed? What do you measure on the VCAPx pins with respect to AVSS?

Regards,

Ryan

Hello Ryan,

Thanks for your reply.

I would like to know how to measure the data rate of nDRDY? (It should be fCLK/8192, right?)

I didn't see any number matched in below picture.

Also used oscilloscope monitoring the DRDY pin on J3.

It seems that the sampling rate of oscilloscope is too low to measure the data rate.

Which pin should i measure on AVSS(JP21)?

AVSS(JP21) 1-2 have jumper connected.

I measured VCAP1(from C9) to AVSS(JP21).3,

It's -1.31 V.

Best regards,

Tim

Hi Ryan,

Thanks for your explanation. As i measured DRDY pin by oscilloscope, it was 250Hz.

Sorry for my typo, it's JP20 exactly.

And yes, VCAP1 respect to AVSS[2] is 1.19V.

Best regards,

Tim

Hi Ryan,

Glad to hear that my device is working properly. I will check my code again.

Thanks for your help.

BR,

Tim

Hi Ryan,

The datasheet says when using 500 SPS, the minimum rate of SCLK is 110k Hz(the end of p.38).

How to calculate the minimum rate of SCLK for other SPS?

I think i found the problem.

In above picture, yellow is SCLK, and red is DOUT signal.

Did the output pulses of DOUT is normal? (It's about only 1V)

And is there anyway to adjust ADS1299 to let DOUT voltage higher?

By the way, I found someone said that ADS1299 has digital input limit at 4.2V,.

I searched 4.2V in datasheet by ctrl+F, but i didn't find any information.

Is it correct that the 4.2V is the limit of ADS1299 digital input?

BR,

Tim

Hello Tim,

The minimum SCLK frequency is calculated by Equation 9 on page 39. Basically, you need to send 216 clock pulses within one data rate period with some margin for timing delays.

It appears that another device is loading the DOUT pin. Is nCS low during this transaction?

Digital inputs are limited by DGND and DVDD supplies. See the Electrical Characteristics section for digital input voltage limits.

Regards,

Ryan

Hello Ryan,

Thanks for telling me where the Equation is.

Yes, i use Arduino Uno to catch DOUT data, and have checked that nCS is low during transaction.

Does the input limit restrict SPI communication for ADS1299?

Now, i'm trying reduce voltage sending to SCLK or DIN.

Best regards,

Tim

Hi Tim,

The digital I/O high and low levels are relative to DVDD. The min and max I/O levels are shown in the data sheet. It is ok to allow SCLK to toggle from 0V to DVDD (there's no need to reduce the levels). However, I suggest to probe the SCLK signal with a scope to confirm there is no excessive over/undershoot or ringing on the clock signal.

Regards,

Ryan

Hello Ryan,

Thanks for your advice. I thought i send SPI signal successfully. 

I sent 4 SPI commands, and SCLK and DOUT shown correct byte pattern. However, when i sent RREG command, i did not get response from ADS1299.

I have checked that MOSI should connect to DIN, MISO connect to DOUT, and nCS worked properly.

(YELLOW is SCLK, BLUE is DIN signal, RED is DOUT signal)

Is there any pin configuration on ADS1299 i do not mention?

Best regards,

Tim

Hi Tim,

What are your master clock (CLK) and serial clock (SCLK) frequencies? Have you checked the tSDECODE timing restriction for multi-byte commands?

[FAQ] ADS129x: What is the minimum frequency for my SCLK? - Data converters forum - Data converters - TI E2E support forums

Regards,

Ryan

Hi Ryan,

CLK was 2.048M Hz as ADS1299 default, and SCLK was set to 4M Hz. Yes, the tSDECODE should be 4 * tCLK(, and i set 3 microseconds as delay time. So i think it's ok?

Could you help recheck jumper setting on ADS1299EEGFE-PDK please?

Is the first pin count from left or count from the side with JPx printed?

Another question is i found that the voltage of DOUT changed not as my expect. I thought that if ADS1299 didn't receive commands, DOUT should be at 0 level. However, when i sending commands the voltage of DOUT change when command sent to ADS1299.

When START command sent(BLUE), the voltage of DOUT signal(RED) had a peak value(1.7V). The baseline of DOUT was also turn up to 0.4V after START command.

(SCLK: YELLOW;  DIN: RED;  DOUT: BLUE;  CS: GREEN)

Below is the three bytes of RREG command.

First, sending RREG command with register address(0010 0000)

Second, sending 000n nnnn to read number of registers. It's 0000 0000 because i only want to read ID register.

Third, sending a dummy bytes to receive ID register.

Is there anything wrong during the RREG commands? In last 2 pictures, the signal of DOUT also turn up to 1.2V every bit sending. Why did it happen?

At last, if above all are correct, I still can't receive any register from ADS1299 by SPI.

Please give me more suggestion.

Best regards,

Tim

Hi Tim,

Could you try uploading the image of your jumper settings again? The link is broken.

Pin 1 of the JPx jumpers is usually designated by a dot in the silkscreen. Also, you can look on the bottom side and pin 1 will have a square pad, while the other pins have a circular pad.

The change in DOUT that you see while sending SPI commands is likely noise coupling from other digital signals, most likely SCLK. Some of this error may actually be introduced by the oscilloscope probes themselves. You can try shortening the ground leads or using a logic analyzer for a cleaner signal.

Regards,

Ryan

Hi Ryan,

Sure, if the picture is not clear, please tell me.

Thanks for your explanation.
According to your explanation, i think my JP2 and JP20 is not default configuration, right?

Let me describe my setting again.
Before using SPI interface, i had tried the software that TI build for ADS1299EEGFE. I could see correct register in the software.
When trying SPI, i connected power supply to MMB0, and measured the test points at p.15. All TPs are matched the datasheet.
According to datasheet, i connected SCLK, DIN, DOUT, nCS, GND to Arduino Uno for SPI communication.
Is there any pin i missed to use SPI?

I also have some curious points.
Would it be MMB0 influence the SPI transmission?
If i want to separate ADS1299 and MMB0, how do i supply power to ADS1299 and do i have to change the jumper configuration?
How to know if ADS1299 receive my commands successfully?

BR,

Tim

Hi Ryan,

Thank you for providing the power supply method.

I think we don't need to look at the pictures in previous reply anymore. Let's focus on the way we going now.
Today, i tried supply power directly on JP2, JP20, JP24, but i couldn't measure any voltage from test points matched datasheet.
Below is my setting.
Orange and red jumper wire connect to JP2, and JP20. Yellow is 3V supply to JP24. GND connects to TP12(To my understanding, all black TPx on the board is the same GND).
(It's not real work, please ignore the 3V without power supply. I will use a voltage regulator or divider to lower the 5V input and supply to JP24).

Is there anything i did wrong? 

"For the SPI signals, you may find that some are available directly on J3, while others pass through a jumper (i.e. nCS connects to JP21). Make sure you are connecting the signals at a point which directly connects to the ADS1299 pins."

According to above, it means i can not use the pins on J3 if the pins directly connects to ADS1299, right?

BR,

Tim

Hi Tim, 

I'm glad to hear everything is working now. Thanks for the feedback!

Regards,

Ryan