AD7770 daisy chain in SPI mode

Hi davec ,

Only the last ADC in the chain has SPI connection to the digital host. In daisy chain mode, the data is propagated from one subnode to the next. Please have a look at the links below for more details on daisy-chain. Thank you!

https://www.analog.com/en/analog-dialogue/articles/introduction-to-spi-interface.html

https://www.analog.com/media/en/technical-documentation/tech-articles/daisychaining-spi-devices.pdf

Thanks,

Janine

Janine,

Thanks for that. For a configuration with two 8 channel ADCs the SPI data stream would have alternate 16 bit data samples from each ADC. The first ADC would have all the odd numbered channels and the other ADC the even ones.

Hi davec ,

Thank you for sharing. Hopefully, your query has been resolved.

Thanks,

Janine.

Janine,

Happy New Year.

Unfortunately we are still unable to find definitive details on daisy chaining the AD7770 ADC in SDI mode. In the technical manual for the AD76630 ADC the wiring and data format is well described. Please advise where we can find the equivalent information for the AD7770.

Regards,

Dave Courtney

Hi davec ,

We are currently looking into this and will get back to you.

Thanks,

Janine

Hi davec ,

Daisy chain mode is only available in DOUT interface and not in SPI interface.

When using daisy chain, DOUT2 and DOUT3 act as input pins that will receive yes data from the previous ADC.

DOUT is not a standard SPI and the ADC generates the clock in daisy chain mode.

Please refer to the figure below for the daisy chain mode configuration using 2 DOUT lines.

Thanks,

Janine

Janine,

Can we still daisy-chain the SPI signals to configure the internal registers?

Hi davec ,

There is no way to configure the SPI signals in daisy chain such that the data will propagate from one ADC to another. Only the DOUT (ADC data) can be daisy chained.

Thanks,

Janine

Janine,

Thanks for that. Presumably we could use SPI using the Chip Selects to configure the internal registers seperately.

Dave

Hi davec ,

You can use the chip selects to configure the internal registers but these cannot be connected in daisy chain.

I hope your issue has been resolved.

Thanks,

Janine

Janine,

Yes. Thanks for all your help.

Regards,

Dave

Hi davec ,

I'm glad we could help. We have added 2 new FAQs for AD777x that may further explain this in case others also encounter the same queries. 

 AD777x: How to configure AD777x in daisy chain mode? 

 AD777x: How to synchronize multiple AD777x? 

Thanks,

Janine

Hi davec ,

I'm glad we could help. We have added 2 new FAQs for AD777x that may further explain this in case others also encounter the same queries. 

 AD777x: How to configure AD777x in daisy chain mode? 

 AD777x: How to synchronize multiple AD777x? 

Thanks,

Janine