ADS131A02: initialization issues

mikael elharrar

Part Number: ADS131A02
Other Parts Discussed in Thread: ADS131A04

Hi TI support team,

I'm working with ADS131A02 and have some problems:

For your information: M0,M1, and M2 are set to 1. (I'm working with 32bits format).

1) After reset, I get the ready word 0xFF02 after several interrupts. Why not after the first one ?
Note that I read 4 bytes each time and get 0xFF|Ox02|0x00|0xBA. I don't know what [ 0x0 | 0xBA ] means.

2) After that, I send NULL (on 4 bytes, with LSB set to 0), and I get 0xFF|0x02|0x00|0xBA. What does that mean ?
See page 50 in datasheet, it is explained that I need to get "Status response, and channel data (???)" during the transfer.
It also happens with 2 bytes format read/write ( then I get only 0xFF|0x02 of course).

3) After that I send UNLOCK command on 4 bytes (0x06|0x55|0x00|0x00) and I get the same thing (0xFF|Ox02|0x00|0xBA).
I should see "ACK(STAT_1)". What does ACK(STAT_1) mean ? Why I don't get it ?

4) Immediately after that I send a read register command on reg 0x0D like:

uint8_t w_byte[4] = {0};
uint8_t r_byte[4] = {0};

w_byte[0] = 0x20;
w_byte[0] |= address;
w_byte[1] = 0;//0; /* number of register minus 1 */

_ads_write_bytes(w_byte, r_byte, 4, 0 /*stay_active*/, 1 /*is_blocking*/);

but I get again: 0xFF|0x02|0x00|0xBA. (according to page 51 in the datasheet I should get the UNLOCK acknoledge ....)

During all of those operations the interrupts dont stop to fire, I don't understand why.

Please help.

Thanks.

over 8 years ago

0 Ryan Andrews over 8 years ago

TI__Guru 67626 points

Hi Mikael,

Thanks for your post!

To answer your first question, the ADS131A04 requires the first few samples to settle following a reset.

Once the device is ready, it will send the READY Command Status Response, beginning with 0xFF 0x02 0x00. The last byte (0xBA) I believe is the Hamming Code output corresponding to those 24 data bits. If you tie M2 to GND, the Command Status Response should come back with 0x00 as the last byte.

I'm still looking into the remaining parts of your question with the IC designer. I will provide an additional update by the end of the week.

Best Regards,

0 mikael elharrar over 8 years ago in reply to Ryan Andrews

Intellectual 825 points

Hi Ryan,

Thanks for your response. I'm waiting for your next update.

Thanks

Mikael

0 Ryan Andrews over 8 years ago in reply to mikael elharrar

TI__Guru 67626 points

Hi Mikael,

It appears that you need to send the Hamming Code with the commands as well. Otherwise, the command will be ignored by the device.

If you do not need the Hamming Code, I would suggest disabling it by tying M2 to GND.

Best Regards,

0 mikael elharrar over 8 years ago in reply to Ryan Andrews

Intellectual 825 points

Thanks Ryan,
Can you point me in the datasheet how to calculate the haming code ? How many bytes length it should be ? It should be included inside the 32 bits word or in addition to the 32 bits command ?

Thanks
Mikael

0 Ryan Andrews over 8 years ago in reply to mikael elharrar

TI__Guru 67626 points

Hi Mikael,

The Hamming Code is an 8-bit word, consisting of 5 Hamming Code bits, 2 checksum bits (i.e. parity bits), and one 0 bit. It should be included at the end of your 24-bit data word such that the total word size is 32 bits (per your M1 setting). Please see Section 9.5.1.7 for more details.

Hamming Code calculations are standard. At the moment, I do not have a good calculator tool that I can share to illustrate how it works step-by-step, but I'm sure there are plenty of examples online that you can reference.

Best Regards,

0 mikael elharrar over 8 years ago in reply to Ryan Andrews

Intellectual 825 points

Thank you Ryan,
Let me check that and I will update you about this ticket.

Thanks
Mikael

0 mikael elharrar over 8 years ago in reply to Ryan Andrews

Intellectual 825 points

Hi Ryan,

Finally I disconnected M2 from Vcc in order to work without hamming code (too complex to process it in the code.

My question now is, why after initialization I continue to get interrupts from the ADS ?

Please note that I didn't enabled the ADC channels yet.

When the interrupts need to stop to fire ?

I expected to get interrupt when the ADS is ready and when I enable the channels.

Thanks

Mikael

0 Ryan Andrews over 8 years ago in reply to mikael elharrar

TI__Guru 67626 points

Hi Mikael

Sorry for my delay. I'm currently looking into this with a colleague and should have an update for you shortly.

Now that you have Hamming Code disabled, could you please share the exact commands you are sending to the device after power-up?

Best Regards,

0 Ryan Andrews over 8 years ago in reply to Ryan Andrews

TI__Guru 67626 points

Hi Mikael,

Once the device completes an internal power-on reset (POR), it will begin to output interrupts on /DRDY. You do not need to send any commands to begin conversions or to allow for /DRDY interrupts.

Best Regards,

0 mikael elharrar over 8 years ago in reply to Ryan Andrews

Intellectual 825 points

Thank you Ryan,

It is exactly what I finnaly did.

Thanks for your help.

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ADS131A02: initialization issues