MCF5253 IntroductionMCF5253 Reference Manual, Rev. 1Freescale Semiconductor 1-13The MCF5253 supports voltage controlled crystal oscillator (VCXO) operation of the oscillator by meansof a 16-bit pulse density modulation output. Using this mode, it is possible to lock the oscillator to thefrequency of an incoming IEC958 or IIS signal. The maximum trim depends on the type and design of theoscillator. Typically a trim of +/- 100 ppm can be achieved with a crystal oscillator and over +/- 1000 ppmwith an LC oscillator.1.5.30 Sleep and Wake-Up ModesThe MCF5253 has a low power Sleep mode where all clocks are disabled and SRAM contents aremaintained. Sleep mode is exited by taking the external Wake-up pin low. Sleep mode is selected bysoftware control of a bit in the PLL register. When Sleep mode is exited code execution resumes from thenext instruction.1.5.31 BootloaderThe MCF5253 incorporates a ROM Bootloader, which enables booting from UART, I2C, SPI or IDEdevices.1.5.32 Internal Voltage RegulatorAn internal 1.2 V regulator can be used to supply the CPU and PLL sections of the MCF5253, reducingthe number of external components required and allowing operation from a single supply rail, typically 3.3volts. However, it must be noted that the internal regulator has an efficiency of less than 50%, and it is notintended for use in battery powered applications, where the use of a highly efficient external DC-DCconverter would be more appropriate.
