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losing bits when reading ABS_POS from L6470

Question asked by lee.jason.008 on Mar 9, 2015
Latest reply on Feb 8, 2018 by karpavicius.linas
Hi,

I am facing an issue where it seems the L6470 drops the most-significant bit of each byte transferred when I GetParam ABS_POS.

Here is a screenshot of the SPI comminucation during the last byte transferred when the ABS_POS is at 0.  To me, L6470 is writing 0000 0001 (binary) to the line.  It seems only 7 bits are transferred before the SO goes back HIGH... or L6470 is seeing the rising CK edge prior to the CS low event.  When I zoom in, I see the CK goes HIGH on the first edge approx. 30ns before CS low.

L6470_ABS_POS.jpg

Does anyone see anything in this image that helps explain the behavior?  Or an I missing some configuration needed for ABS_POS to work correctly? 

Thanks for any help you can provide.  Right now, I'm stumped....

Jason.

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