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K60 SPI Slave issue: extra byte exist

Question asked by Shen Li on Aug 19, 2013
Latest reply on Oct 23, 2014 by Marcelo Varanda

I am using K60 as SPI Slave mode. my code push the data frame (0x55,0x55,0x55,0x11,...)to the TXFIFO and wait the SPI Master to read out. But the master will read out the data frame as (0x0,0x55,0x55,0x55,0x11,....). I do not know why there is an extra '0x0' received. I grab the bus wave and found the 0x0 is sent on the MISO .Please refer to the attached pic. I did debug by step-by-step check the FIFO filling action,and no issue occured, no '0x0' was insert into the fifo.

Why the SPI controller will add an 0x0?

screenshot.png

 

Btw, I found in the K60 RM(50.4.6 Slave Mode Operation Constraints), it said "The transmit data is transferred at second SCK clock edge of the each frame to the shift

register if the SS signal is asserted and any time when transmit data is ready and SS signal is negated."

 

What is this mean? Does the issue related with this?

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