AnsweredAssumed Answered

SHARC ADSP-21489 SPI slave transmitting extra leading zero byte

Question asked by davidashman on Feb 3, 2015
Latest reply on Mar 19, 2015 by jobo23

Hello -

 

The SPI slave bus on my SHARC ADSP-21489 is transmitting one extra leading zero byte on MISO line.

 

I use the SHARC SPI B bus in slave mode to communicate with an external master device.  The master device sends a SPI write command followed by a SPI read command.  At SHARC power up, I flush DMA FIFO, flush TX and RX registers, and set the appropriate registers for an RX message via DMA per the ADSP-214xx SHARC Processor Hardware Reference document.  The RX message is properly received and processed by the SHARC.  I then flush DMA FIFO, flush TX and RX registers, and set the appropriate registers for a TX message.  I'm finding that the SHARC sends out a leading zero byte on the MISO line in response to the SPI read command from the external device.  The correct TX message buffer address is in the SHARC DMA register which contains the start of my data to be sent.  After the leading zero byte on MISO, all data is correct and matches the TX message buffer.

 

Do you have any idea why this extra leading zero byte is being sent out?

 

Thanks,

Dave

Outcomes