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Howto: 20-bit SPI transfer using SSP?

Question asked by Dave Nadler on Oct 16, 2018
Latest reply on Oct 18, 2018 by Kerry Zhou

Considering using LPC MCUs for a project.

 

Need to interface to devices with 20-bit SPI frames, which is very common (for 20-bit ADCs, DACs, etc); for example:

http://www.ti.com/lit/ds/symlink/ads8904b.pdf

https://www.maximintegrated.com/en/ds/MAX5717-MAX5719.pdf

Note in particular the CS requirements in the either datasheet above (CS must be held low for 20-bit duration).

There many other 20-bit SPI parts with similar requirements.

 

I had a quick read of the LPC176x SSP description here: https://www.nxp.com/docs/en/user-guide/UM10360.pdf 

I can't see how one does a transfer longer than 16 bits (which is supported for example on Kinetis SPI).

 

How does one do a 20-bit SPI transfer?
Does this apply across all LPC family devices or do some have different SPI capabilities?

 

Thanks in advance,
Best Regards, Dave

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