DAC60508: did not work through spi

Hynag Chung

Intellectual 980 points

Part Number: DAC60508
Other Parts Discussed in Thread: CC2640

Hi, I am trying to use DAC60508 with cc2640.

I sent data set 0x0a0fff through spi expecting out2 to be full voltage but it did not work.

I checked all spi signals is working well but it did not work.

I attached my code and could you check it?

Thank you.

over 7 years ago

0 Uttam Sahu over 7 years ago

TI__Genius 14220 points

Hi Hynag,

Thank you for your query. i am not an expert on CC2640. However, the SPI config (CPOL=0, CPHA=1) looks fine in your code. But I am not sure how the /CS would look like. Please make sure it is active for the entire 24 bits and not becoming HIGH every 8 bits.

One reason you might not be seeing full voltage is that the data is not MSB aligned. So, in order to write 0xFFF to channel 2, you need to write 0x0A FF F0.

If you are still facing a problem, please upload scope shots of the SPI frame for further debugging.

Regards,
Uttam Sahu
Applications Engineer, Precision DACs

0 Hynag Chung over 7 years ago in reply to Uttam Sahu

Intellectual 980 points

Hi,

I set tx data 0x0afff0 as you said, but output is only 300mV.

I attached scope shots. And I have a question about sdo. I check sdo signal and got output like second one. It looks like 0x0a0bff0.

does this mean register in DAC is 0x0bff0?

Thank you.

0 Uttam Sahu over 7 years ago in reply to Hynag Chung

TI__Genius 14220 points

Hi Hynag,

I think the yellow trace is /CS. Itseems it is going HIGH every 8 bits. That is not a valid pattern. I am not sure whether the controller supports that or not. or else, you need to use a GPIO as the /CS signal and switch it LOW or HIGH using software.

Hope that answers.

Regards,
Uttam

0 Hynag Chung over 7 years ago in reply to Uttam Sahu

Intellectual 980 points

Then /cs must be low while transferring 24bit, but my signal is getting high every 8 bits. is this correct?

0 Uttam Sahu over 7 years ago in reply to Hynag Chung

TI__Genius 14220 points

You're right. In many controllers the SPI engine is meant for 8 o 16-bits only. But precision DAC's and ADC's usually have a packet size of more than 16-bits. That's why a separate /CS is needed.

Regards,
Uttam

0 Hynag Chung over 7 years ago in reply to Uttam Sahu

Intellectual 980 points

Now I know what was the problem. Thank you for your help:)

0 Hynag Chung over 7 years ago in reply to Uttam Sahu

Intellectual 980 points

Hi,

Even though I set /cs low while transferring data, output voltage is still low.

I attached signal picture so please take a look and see if I transfer proper data set.

I sent 0x0aff08 from master.

0 Uttam Sahu over 7 years ago in reply to Hynag Chung

TI__Genius 14220 points

Hi Hynag,

Could you please send the SCLK and SDIN together in place of /CS? This will help me interpret the data properly.

Regards,
Uttam

0 Hynag Chung over 7 years ago in reply to Uttam Sahu

Intellectual 980 points

Here it is.

0 Uttam Sahu over 7 years ago in reply to Hynag Chung

TI__Genius 14220 points

Hi Hynag,

The SPI patten looks fine. It's 0x0AFF08. In case you are still getting zero output, I would check the reference divider setting. I don't see that in the code you have posted. Please look at the reference input specs in section 7.3 of the datasheet.

Regards,
Uttam

0 Hynag Chung over 7 years ago in reply to Uttam Sahu

Intellectual 980 points

Thank you for your help.

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DAC60508: did not work through spi