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      • Interfacing a 32.768kHz xtal with Si443x

        Silicon_Labs | 02/58/2013 | 10:13 AM
        Question

         

        How the 32.768kHz crystal is suggested to be used?
        1. One of the pins of the crystal needs to be connected to GPIO1, but where shall I connect the second pin?
        2. Is a capacitor required (if so what value) for the crystal operation?




        Answer

         

        A1: The crystal has to be connected between GPIO_0 and GND! Please find our reference design, with the schematic and the xtal setup (Q2).


        A2. The capactitor is not required for normal operation. The placeholder (C5, N.F. - not fitted) is on the board for debug purposes. Using a 0.5pF series capacitor the crystal operation can be monitored without influencing its operation.


        Here is some help from the datasheet p56.:
        'A 32 kHz XTAL may also be used for better timing accuracy. By setting the x32 ksel bit in Register 07h 'Operating
        & Function Control 1', GPIO0 is automatically reconfigured so that an external 32 kHz XTAL may be connected to
        this pin. In this mode, the GPIO0 is extremely sensitive to parasitic capacitance, so only the XTAL should be
        connected to this pin with the XTAL physically located as close to the pin as possible. Once the x32 ksel bit is set,
        all internal functions such as WUT,micro-controller clock, and LDC mode will use the 32 kHz XTAL and not the
        32 kHz RC oscillator.'