HT85F2270 datasheet(60/226 Pages) HOLTEK

60 / 226 page

Rev. 1.00

60 of ��6

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Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

21 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

important in battery powered portable applications. This usually requires the microcontroller can

provide a range of clock sources which can be dynamically selected.

System Clocks Description

The fast clocks required for high performance will inherently have a higher power consumption

and of course vice-versa, lower speed clocks will have a lower power consumption. As Holtek has

provided these devices with a range of oscillators and a PLL function the user can optimise the

system clock frequency to achieve the best performance/power ratio. In addition to the two high

frequency system oscillators, two low frequency 32kHz oscillators are also provided as clock

sources for the WDT and Time Base.

The MCU system clock is sourced from the high speed external crystal, HXT oscillator, or internal,

HIRC oscillator. These oscillators can be used directly as the system clock and can be routed via an

internal PLL to give a wide range of operating frequencies. The PLL frequency can be dynamically

changed to suit varying operating conditions and to achieve maximum performance.

The system clock, namely fSYS, can also be used as a clock source for the peripheral functions, such

as WDT, Time Base, Timers, UART, I2C, SPI, ADC and DAC. Refer to the related sections for the

clock source selections.

HT85F2270 Datasheet(PDF) 60 Page - Holtek Semiconductor Inc