BLUENRG-1 datasheet(28/173 Pages) STMICROELECTRONICS

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Functional details

BlueNRG-1

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DocID028866 Rev 1

The conversion can be single (CONT = 0) or continuous (CONT = 1). In continuous mode,

the conversion runs with a preprogrammed sampling rate, while in single step mode the

ADC performs a conversion and then stops.

The output data rate depends on DECIM_RATE according to the table below.

Table 23: ADC data rate

DECIM_RATE

Output data rate [Ksample/s]

0 (200)

1 (100)

2 (64)

15.625

3 (32)

31.25

The system can work in conjunction with an external MEMS microphone by setting

MIC_SEL. In this mode, an IO configured as PDM_CLK provides the clock to the external

microphone, while an IO configured as PDM_DATA received the PDM stream from the

external microphone. The external clock is 1.6 MHz (DIG_FILT_CLK = 0) or 0.8 MHz

(DIG_FILT_CLK = 1).

The output data rate changes with DECIM_RATE according to Table 24: "ADC data rate

with microphone mode".

Table 24: ADC data rate with microphone mode

DIG_FILT_CLK

DECIM_RATE

Output data rate [Ksample/s]

1 (clock = 0.8 MHz)

0 (200)

1 (100)

2 (64)

12.5

3 (32)

0 (clock = 1.6 MHz)

0 (200)

1 (100)

2 (64)

3 (32)

3.6.2.1

ADC start conversion

The ADC both analog and digital sub-system are switched on by setting ADCON and

SWSTART.

The conversion operation consists of four phases.

The wake-up phase lasts 5 us, is present at the beginning of a single acquisition, with

the goal to let the analog system to settle before to start the acquisition.

If the CALEN is set, a calibration phase is performed. It permits to compensate the

offset in the analog part. The conversion status is tracked by SR status register. At the

beginning of the conversion the BUSY bit is set and masks any attempt to change

CONF, up to the end of the conversion. At end of this conversion, the ENDCAL flag is

generated and the OFFSET register is written with the converted offset voltage.

The acquisition phase is regulated by a timeout depending on the resolution. In this

phase, digital filter chain processes the data coming from ADC.

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