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数据搜索系统，热门电子元器件搜索 |
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ZUSBOPTSC01ZAC 数据表(PDF) 254 Page - Zilog, Inc. |
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ZUSBOPTSC01ZAC 数据表(HTML) 254 Page - Zilog, Inc. |
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254 / 402 page  Oscillator Control P R E L I M I N A R Y PS024604-1005 Z8 Encore!® Motor Control Flash MCUs Product Specification 232 Unintentional accesses to the Oscillator Control Register (OSCCTL) can stop the chip by switching to a nonfunctioning oscillator. Accidental alteration of the OSCCTL register is prevented by a locking/unlocking scheme. To write the register, unlock it by making two writes to the OSCCTL register with the values E7H followed by 18H. A third write to the OSCCTL register then changes the value of the register and returns the register to a locked state. Any other sequence of oscillator control register writes has no effect. The values written to unlock the register must be ordered correctly, but need not be consecutive. It is possible to access other registers within the locking/unlocking operation. Clock Selection Following System Reset The Internal Precision Oscillator is selected following a System Reset. Startup code after the System Reset may change the system clock source by unlocking and configuring the OSCCTL register. If the LPDEN bit in Program Memory Address 0001H is zero, Flash Low Power mode is enabled during reset. When Flash Low Power mode is enabled during reset, the FLPEN bit in the Oscillator Control Register (OSCCTL) will be set and the DIV field of the OSCDIV register will be set to 08h. Clock Failure Detection and Recovery for Primary Oscillator The Z8FMC16100 Series Flash MCU generates a System Exception when a failure of the primary oscillator occurs if the POFEN bit is set in the OSCCTL Register. To maintain sys- tem function in this situation, the clock failure recovery circuitry automatically forces the Table 129. Oscillator Configuration and Selection Clock Source Characteristics Required Setup Internal Precision Oscillator • 5.5296MHz • High precision possible when trimmed • No external components required • This is the reset default. External Crystal/ Resonator/ External Clock Drive • 0 to 20MHz • Very high accuracy (dependent on crystal/resonator or external source) • Requires external components • Configure Option Bits for correct external oscillator mode • Unlock and write Oscillator Control Register (OSCCTL) to enable external oscillator • Wait for required stabilization time • Unlock and write Oscillator Control Register (OSCCTL) to select external oscillator Internal Watchdog Timer Oscillator • 10KHz nominal • Low accuracy • No external components required • Low power consumption • Unlock and write Oscillator Control Register (OSCCTL) to enable and select Internal WDT oscillator |
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