HT45F23 datasheet(39/152 Pages) HOLTEK

39 / 152 page

It should be noted that, no matter what condition the LXTLP bit is set to, the LXT oscillator will always

function normally, the only difference is that it will take more time to start up if in the Low-power

mode.

Internal 32kHz Oscillator

- LIRC

The Internal 32kHz System Oscillator is one of the low frequency oscillator choices, which is selected

via configuration option. It is a fully integrated RC oscillator with a typical frequency of 32kHz at 5V,

requiring no external components for its implementation. Device trimming during the manufacturing

process and the inclusion of internal frequency compensation circuits are used to ensure that the

influence of the power supply voltage, temperature and process variations on the oscillation frequency

are minimised. As a result, at a power supply of 5V and at a temperature of 25

°C degrees, the fixed

oscillation frequency of 32kHz will have a tolerance within 10%.

Supplementary Oscillators

The low speed oscillators, in addition to providing a system clock source are also used to provide a

clock source to two other device functions. These are the Watchdog Timer and the Time Base

Interrupts.

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 battery powered portable applications. The fast clocks required 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 performance/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 configuration options and register

programming, a clock system can be configured to obtain maximum application performance.

The main system clock, can come from either a high frequency, 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, EC or HIRC oscillator, selected via a configuration

option. The low speed system clock source can be sourced from internal clock fL.IffL is selected 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 peripheral circuits, the substitute clock, fSUB, and the

Period Time 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 provide a substitute clock for

the microcontroller just after a wake-up has occurred to enable faster wake-up times.

Together with fSYS/4 it is also used as one of the clock sources for the Watchdog timer. The fTB clock is

used as a source for the Time Base 0/1 interrupt functions.

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

Rev. 1.20

September 15, 2011

HT45F23 Datasheet(PDF) 39 Page - Holtek Semiconductor Inc

HT45F23 Datasheet(HTML) 39 Page - Holtek Semiconductor Inc

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