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HT66F40 数据表(PDF) 43 Page - Holtek Semiconductor Inc |
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HT66F40 数据表(HTML) 43 Page - Holtek Semiconductor Inc |
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43 / 244 page  HT68F20/HT68F30/HT68F40/HT68F50/HT68F60 HT68FU30/HT68FU40/HT68FU50/HT68FU60 Rev. 1.60 43 October 24, 2011 Operating Modes and System Clocks Present day applications require that their microcontrollers have high performance but often still demand that they consume as little power as possible, conflicting requirements that are especially true in bat- tery powered portable applications. The fast clocks re- quired for high performance will by their nature increase current consumption and of course vice-versa, lower speed clocks reduce current consumption. As Holtek has provided these devices with both high and low speed clock sources and the means to switch between them dynamically, the user can optimise the operation of their microcontroller to achieve the best perfor- mance/power ratio. System Clocks The device has many different clock sources for both the CPU and peripheral function operation. By providing the user with a wide range of clock options using config- uration options and register programming, a clock sys- tem can be configured to obtain maximum application performance. The main system clock, can come from either a high fre- quency, fH, or low frequency, fL, source, and is selected using the HLCLK bit and CKS2~CKS0 bits in the SMOD register. The high speed system clock can be sourced from either an HXT, ERC or HIRC oscillator, selected via a configuration option. The low speed system clock source can be sourced from internal clock fL.IffL is se- lected then it can be sourced by either the LXT or LIRC oscillators, selected via a configuration option. The other choice, which is a divided version of the high speed system oscillator has a range of fH/2~fH/64. There are two additional internal clocks for the periph- eral circuits, the substitute clock, fSUB, and the Time Base clock, fTBC. Each of these internal clocks are sourced by either the LXT or LIRC oscillators, selected via configuration options. The fSUB clock is used to pro- vide a substitute clock for the microcontroller just after a wake-up has occurred to enable faster wake-up times. fTBC fSYS/4 TBCK fSUB fSYS/4 fTB fS Configuration Option Time Base WDT HXT ERC HIRC LIRC LXT 6-stage Prescaler High Speed Oscillation Low Speed Oscillation Low Speed Oscillation Configuration Option High Speed Oscillation Configuration Option fH fH/2 fH/4 fH/8 fH/16 fH/32 fH/64 fL HLCLK, CKS2~CKS0 bits Fast Wake-up from SLEEP Mode or IDLE Mode Control (for HXT only) fSYS fSUB System Clock Configurations Note: When the system clock source fSYS is switched to fL from fH, the high speed oscillation will stop to conserve the power. Thus there is no fH~fH/64 for peripheral circuit to use. |
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