80C186EB/80C188EB Microprocessor User's Manual - CEUNES

CLOCK GENERATION AND POWER MANAGEMENTThe first step in determining the proper C PD value is startup time characterization for the crystaloscillator circuit. This step can be done with a storage oscilloscope if you compensate for scopeprobe loading effects. Characterize startup over the full range of operating voltages and temperatures.The oscillator starts up on the order of a couple of milliseconds. After determining the oscillatorstartup time, refer to “PDTMR Pin Delay Calculation” in the data sheet. Multiply thestartup time (in seconds) by the given constant to get the C PD value. Typical values are less than1µF.If the design uses an external oscillator instead of a crystal, the external oscillator continues runningduring Powerdown mode. Leave the PDTMR pin unconnected and the processor can exitPowerdown mode immediately.5.2.3 Implementing a Power Management SchemeTable 5-2 summarizes the power management options available to the user. Overall power consumptionhas two parts: switching power dissipated by driving loads such as the address/data bus,and device power dissipated internally by the microprocessor whether or not it is connected toexternal devices. A power management scheme should consider loading as well as the raw specificationsin the processor's data sheet.Table 5-2. Summary of Power Management ModesModeRelativePowerTypicalPowerUserOverheadChiefAdvantageActive Full 250 mW at 16 MHz — Full-speed operationIdle Low 175 mW at 16 MHz Low Peripherals are unaffectedPowerdown Lowest 250 µW Low to Moderate Long battery lifeNOTEIf an NMI or external maskable interrupt service routine is used to enter apower management mode, the interrupt request signal should be deassertedbefore entering the power management mode.5-19