Table 25-7. Oscillator ModesMode Frequency RangeHigh-frequency mode1, high-gain fosc_hi_1 (3 MHz) up to fosc_hi_1 (8 MHz)High-frequency mode1, low-powerNOTEFor information about low power modes of operation used inthis chip and their alignment with some OSC modes, refer tothe chip's Power Management details.25.8.2.1 Low-Frequency, Low-Power ModeIn low-frequency, low-power mode, the oscillator uses a gain control loop to minimizepower consumption. As the oscillation amplitude increases, the amplifier current isreduced. This continues until a desired amplitude is achieved at steady-state. This modeprovides low pass frequency filtering as well as hysteresis for voltage filtering andconverts the output to logic levels. In this mode, the internal capacitors could be used, theinternal feedback resistor is connected, and no external resistor should be used.In this mode, the amplifier inputs, gain-control input, and input buffer input are allcapacitively coupled for leakage tolerance (not sensitive to the DC level of EXTAL).Also in this mode, all external components except for the resonator itself are integrated,which includes the load capacitors and feeback resistor that biases EXTAL.25.8.3 CounterThe oscillator output clock (OSC_CLK_OUT) is gated off until the counter has detected4096 cycles of its input clock (XTL_CLK). After 4096 cycles are completed, the counterpasses XTL_CLK onto OSC_CLK_OUT. This counting time-out is used to guaranteeoutput clock stability.25.8.4 Reference Clock Pin RequirementsThe OSC module requires use of both the EXTAL and XTAL pins to generate an outputclock in Oscillator mode, but requires only the EXTAL pin in External clock mode. TheEXTAL and XTAL pins are available for I/O. For the implementation of these pins onthis device, refer to the Signal Multiplexing chapter.Chapter 25 Oscillator (OSC)KL25 Sub-Family Reference Manual, Rev. 3, September 2012Freescale Semiconductor, Inc. 413
