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AS3932

Datasheet - Detailed Descr i p ti on

Figure 20. Concept of the False Wake-up Register together with the system

8.8 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 the calibration

must be done every time after the RCO is turned off. The RCO is turned off when the chip is in power down mode, a POR happened, or the

crystal oscillator is enabled. 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

Level 1

Wakeup

Level 2

WAKE

False wakeup

register

Unsuccessful

pattern

correlation

Register Setup

Microcontroller

READ FALSE WAKEUP REGISTER