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ADC cycles/conversion in burst mode

Question asked by Martin Lorenz on Jun 30, 2016
Latest reply on Aug 2, 2016 by Hui_Ma

I do sound recording with the ADC of LPC1549 in burst mode. The sequence includes just one channel.


I just would like to inform the forum that the ADC in LPC1549 needs 26 cycles of the ADC clock for a complete conversion when doing continous sampling.

This is in contradiction with the manual which states that a full 12bit conversion needs 25 cycles!


I observed that the calculated frequency of a sampled sinus is exactly a factor 25/26 lower than expected. Then I counted the cpu cycles for 1024 samples with DWT counter and I confirmed the result.


Dear LPC support, could you please update the manual with this respect?

Perhaps I configured the ADC wrong, so that it needs an extra cycle to restart the conversion after a completion?

Perhaps the same behaviour can be observed in other LPCxxxx ADCs?


Update: I'm using synchronous mode, and I do not use any ADC interupts. The ADC is triggered manually by SW.