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What is the difference between the two power reduction registers PR.PRPA and PR.PRPB on the XMEGA B family chips?

They share a single entry in the data sheet...

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...with the same defined bits... but they are, in fact, two separate registers each with their own addresses... enter image description here

There is only one ADC and one AC on this chip, so what happens if I, say, set ADC the bit in only one of the two PR registers? Is the clock to the ADC stopped? Or do I have to set the bit in both registers?

Where is this documented?

bigjosh
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2 Answers2

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This single line at the very end of the ADC section of the ATXMEGA64B3 data sheet references the ADCB name for the ADC...

PORTB has one ADC. Notation of this peripheral is ADCB

There is no corresponding line for an ADCA (although this peripheral is referenced several other places in the datasheet). Note that the single ADC on this device is also called just ADC in the header files.

I've empirically tested and the PPR bits and, in fact, the PPRB bit does disable the single ADC on this part. The PPRA bit, while defined in the headers, is not actually implemented on this device so setting it has no effect.

bigjosh
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Judging by what is below them in the data sheet, namely PRPC/D/E/, A/B refers to the port that the peripheral is on, and looking at the block diagram confirms this. Namely, there are separate ADCs, DACs, and comparators for port A and B, so setting the ADC bit in PRPA powers down the ADC for port A, but not the ADC for port B.

Though I agree, this should have been explained better in the documentation.

C_Elegans
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  • I see the ADCA and ADCB on that same block diagram, but I can't figure out what they are referring to. There is only one ADC on the chip and it is called just ADC not ADCA or ADCB. All the ADC registers are similarly named ADC.*. Could be a cut-and-paste error from another part, but also both PR registers are defined in the io.h. Hmmm... – bigjosh Feb 25 '18 at 03:47