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AS3932

Most wakeup receivers have to deal with environments that can rapidly change. By periodically monitoring the number of false wakeup events it

is possible to adapt the system setup to the actual characteristics of the environment and enables a better use of the full flexibility of AS3932.

Note:

If the Manchester decoder is enabled, the false wakeup register is not able anymore to store the false wakeup events.

Figure 21. Concept of the False Wakeup Register together with the system

8.9 Real Time Clock (RTC)

The RTC can be based on a crystal oscillator (R1<0>=1), the internal RC-oscillator (R1<0>=0), or an external clock source (R1<0>=1). The

crystal oscillator has higher precision of the frequency with higher current consumption and needs three external components (crystal plus two

capacitors). The RC-oscillator is completely integrated and can be calibrated if a reference signal is available for a very short time to improve the

frequency accuracy. The calibration gets started with the trim_osc direct command. Since no non-volatile memory is available on the chip, the

calibration must be done every time after battery replacement. Since the RTC defines the time base of the frequency detection, the selected

frequency (frequency of the crystal oscillator or the reference frequency used for calibration of the RC oscillator) should be about one forth of the

carrier frequency:

(EQ 1)

Where:

The third option for the RTC is the use of an external clock source, which must be applied directly to the XIN pin (XOUT floating).

Frequency Detector

Pattern Correlator

Wakeup

Level1

Wakeup

Level2

WAKE

False wakeup

register

Unsuccessful

pattern

correlation

Register Setup

Microcontroller

READ FALSE WAKEUP REGISTER