mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 477

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

Chapter 21 Oscillator (OSC)
21.8.2.3 High-Frequency, High-Gain Mode
In high-frequency, high-gain mode, the oscillator uses a simple inverter-style amplifier.
The gain is set to achieve rail-to-rail oscillation amplitudes. This mode provides low pass
frequency filtering as well as hysteresis for voltage filtering and converts the output to
logic levels. In this mode, the internal capacitors could be used.
21.8.2.4 High-Frequency, Low-Power Mode
In high-frequency, low-power mode, the oscillator uses a gain control loop to minimize
power consumption. As the oscillation amplitude increases, the amplifier current is
reduced. This continues until a desired amplitude is achieved at steady-state. In this
mode, the internal capacitors could be used, the internal feedback resistor is connected,
and no external resistor should be used.
The oscillator input buffer in this mode is differential. It provides low pass frequency
filtering as well as hysteresis for voltage filtering and converts the output to logic levels.
21.8.3 Counter
The oscillator output clock (OSC_CLK_OUT) is gated off until the counter has detected
4096 cycles of its input clock (XTL_CLK). After 4096 cycles are completed, the counter
passes XTL_CLK onto OSC_CLK_OUT. This counting time-out is used to guarantee
output clock stability.
21.8.4 Reference Clock Pin Requirements
The OSC module requires use of both the EXTAL and XTAL pins to generate an output
clock in Oscillator mode, but requires only the EXTAL pin in External clock mode. The
EXTAL and XTAL pins are available for I/O. For the implementation of these pins on
this device, refer to the Signal Multiplexing chapter.
21.9 Reset
There is no reset state associated with the OSC module. The counter logic is reset when
the OSC is not configured to generate clocks.
There are no sources of reset requests for the OSC module.
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Preliminary
Freescale Semiconductor, Inc.
477