NRF52811-QCAA-R datasheet(131/444 Pages) NORDIC

131 / 444 page

Peripherals

MODE.OPERATION

Bits per sample

Result stored per RAM

word

Physical RAM allocated

(32 bit words)

Result boundary indexes

in RAM

Note

Stereo

32 (2x16)

L+R

ceil(SAMPLE.MAXCNT/2) R0=[31:16]; L0=[15:0]

Default

Mono

2xL

ceil(SAMPLE.MAXCNT/2) L1=[31:16]; L0=[15:0]

Table 43: DMA sample storage

The destination buffer in RAM consists of one block, the size of which is set in SAMPLE.MAXCNT register.

Format is number of 16-bit samples. The physical RAM allocated is always:

(RAM allocation, in bytes) = SAMPLE.MAXCNT * 2;

(but the mapping of the samples depends on MODE.OPERATION.

If OPERATION=Stereo, RAM will contain a succession of Left and Right samples.

If OPERATION=Mono, RAM will contain a succession of mono samples.

For a given value of SAMPLE.MAXCNT, the buffer in RAM can contain half the stereo sampling time as

compared to the mono sampling time.

The PDM acquisition can be started by the START task, after the SAMPLE.PTR and SAMPLE.MAXCNT

registers have been written. When starting the module, it will take some time for the filters to start

outputting valid data. Transients from the PDM microphone itself may also occur. The first few samples

(typically around 50) might hence contain invalid values or transients. It is therefore advised to discard the

first few samples after a PDM start.

As soon as the STARTED event is received, the firmware can write the next SAMPLE.PTR value (this register

is double-buffered), to ensure continuous operation.

When the buffer in RAM is filled with samples, an END event is triggered. The firmware can start

processing the data in the buffer. Meanwhile, the PDM module starts acquiring data into the new buffer

pointed to by SAMPLE.PTR, and sends a new STARTED event, so that the firmware can update SAMPLE.PTR

to the next buffer address.

6.10.5 Hardware example

Connect the microphone clock to CLK, and data to DIN.

CLK

Vdd

DATA

L/R

CLK

DIN

nRFxxxxx

CLK

DIN

Figure 42: Example of a single PDM microphone, wired as left

CLK

Vdd

DATA

L/R

CLK

DIN

nRFxxxxx

CLK

DIN

Figure 43: Example of a single PDM microphone, wired as right

4454_140 v1.0

131

NRF52811-QCAA-R Datasheet(PDF) 131 Page - Nordic Semiconductor

NRF52811-QCAA-R Datasheet(HTML) 131 Page - Nordic Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL