BLUENRG-2 datasheet(33/190 Pages) STMICROELECTRONICS

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BlueNRG-2

Functional details

DocID030675 Rev 2

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Table 30: Output data rate with microphone

DIG_FILT_CLK

OSR

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.

The elaboration phase is at the end of the timeout, the data obtained at the output of

the digital filter is written in the DATA register. If the calibration is on, the output of the

digital filter is de-embedded considering the content of the OFFSET register.

Furthermore, the ADCEOC flag is generated to warn about the end of conversion. If

ENAB_COMP bit is set, the WDOG flag is generated to warn that the result of the

conversion is between a high THRESHOLD_HI and low threshold THRESHOLD_LO.

It is always advisable to set the register field CALEN in order to perform automatic

calibration for each measurement.

3.6.2.2

ADC offset

The ADC can automatically correct the offset error.

To enable the automatic offset correction the CALEN and the OFFSET_UPDATE must be

set. The result of the last calibration is stored in the OFFSET register.

The correction of the offset can be also done manually, for example by making a

conversion of the internal channel InP = InN = 0.6 V and after that, writing the result of

conversion in the OFFSET register.

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