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Wrong last 7 bits of 32bit SPORT received word

Question asked by daguiam on May 11, 2013
Latest reply on May 21, 2013 by daguiam



I am trying to receive a sample from two chained 16 bit AD7685 ADCs which results in a 32 bit word with a leading busy signal which works as an interruption to start the sport interface of an ezkit lite 21369. The ADC is connected to the DAI ports.

The issue is that the received sample is correct but for the last 7 bits, which are zeros despite what is on the data line. I attach the scope of these signals where ch1 is Data, ch3 is clock and ch4 is the frame sync. Disregard the noise in the frame sync line since it is a result of the long probes.


From the scope, I can see that the word i was supposed to receive is 0x62755ffa but I am receiving 0x62755f80. I consistently get zeros on the last 7 bits.

My sport interface is configured in standard serial mode and an SLEN of 32 bits, internal clock and internal frame sync. I do not understand why the last few bits are stuck at zero, since the SPORT isn't disabled until much after and there is no changed in the data line SRU.


Any help is appreciated!