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Triggering SAR ADC conversion with BCTU, followed by a DMA transfer on the MPC5746R

Question asked by Eric Karr on Aug 9, 2017
Latest reply on Sep 20, 2017 by Eric Karr



I am using the PIT, to trigger the BCTU, to collect SAR ADC readings. I then want to use the BCTU to trigger a DMA transfer that will push that data into a location in RAM. So far, I successfully have the PIT, triggering the BCTU, which is gathering results from SAR2 ADC, and I can read them back in the BCTU ADC2DR register. I also have, a successful memory to memory DMA transfer setup, that I can trigger manually from software.


My belief, is that I should use the DMAMUX to configure the source of the DMA transfer, if so, then I am unsure if the source should be the BCTU, or the SAR of which the conversion is being triggered on. I have attached a screenshot of an excerpt from the reference manual with highlights to my references.


One of my confusions, is the reference to 'BCTU_n' in said table. I say that, because there is only a singular BCTU module in the MPC5746R. But, I am making the assumption, that 'BCTU_2' would align with a trigger from a completed conversion on SAR channel 2 through the BCTU.


I have tried using 'BCTU_2' as a source for my DMA transfer, on DMA channel 0, through DMAMUX 0. For DMA, I am using round robin groups and fixed priority channels within those groups. Then, I have also tried using 'SAR_ADC_2' as a trigger on DMAMUX 1, with a DMA channel of 16. I always configure my DMA channels before the MUX channels.


I can provide additional information, and code, if required. Just curious what I could be missing. Like I said, the PIT, BCTU, and SAR, have all been tested together successfully. As well as a DMA transfer from memory-to-memory, on various other channels.


Thank you very much for the help.