TN235 - External 32.768 kHz Oscillator Circuits - Rabbit - #1

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022-0084 Rev. G 1 TN235 External 32.768 kHz Oscillator Circuits An external 32.768 kHz clock is an essential part of any Rabbit-based system. Besides driving the realtime clock, the 32.768 kHz clock is used by various processor and peripheral subsystems that are used extensively by Dynamic C software. It is therefore recommended that an external 32.768 kHz oscillator circuit always be implemented. It is possible to operate the Rabbit without a 32.768 kHz clock, but several key features will not be available. Without the 32.768 kHz clock, the real-time clock, the watchdog timer, the periodic interrupt, and asynchronous remote bootstrap will not function. Neither will any of the low-power features that run off the 32.768 kHz clock. Figure 1 shows the basic concept behind the external CMOS crystal oscillator circuits used in Rabbitbased products. The crystal used in the circuit is a parallel resonant crystal. Figure 1. Basic 32.768 kHz Oscillator Circuit NOTE: The value of C1 may vary from system to system, or C1 may be completely eliminated depending on the crystal CL, the amount of frequency deviation from 32.768 kHz, and the measured drive through the crystal.
  
               

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