HT67F60 datasheet(56/242 Pages) HOLTEK

56 / 242 page

Rev. 1.50

March 06 , 2012

Rev. 1.50

March 06 , 2012

HT67F30/HT67F40/HT67F50/HT67F60

TinyPowerTM A/D Flash Type 8-Bit MCU with LCD & EEPRO

Internal RC Oscillator – HIRC

The internal RC oscillator is a fully integrated system oscillator requiring no external components.

The internal RC oscillator has three fixed frequencies of either 4MHz, 8MHz or 12MHz. 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 either 3V or

5V and at a temperature of 25°C degrees, the fixed oscillation frequency of 4MHz, 8MHz or 12MHz

will have a tolerance within 2%. Note that if this internal system clock option is selected, as it

requires no external pins for its operation, I/O pins PB1 and PB2 are free for use as normal I/O pins.

External 32.768kHz Crystal Oscillator – LXT

The External 32.768kHz Crystal System Oscillator is one of the low frequency oscillator choices,

which is selected via configuration option. This clock source has a fixed frequency of 32.768kHz

and requires a 32.768kHz crystal to be connected between pins XT1 and XT2. The external resistor

and capacitor components connected to the 32.768kHz crystal are necessary to provide oscillation.

For applications where precise frequencies are essential, these components may be required to

provide frequency compensation due to different crystal manufacturing tolerances. During power-up

there is a time delay associated with the LXT oscillator waiting for it to start-up.

When the microcontroller enters the SLEEP or IDLE Mode, the system clock is switched off to stop

microcontroller activity and to conserve power. However, in many microcontroller applications it

may be necessary to keep the internal timers operational even when the microcontroller is in the

SLEEP or IDLE Mode. To do this, another clock, independent of the system clock, must be

provided.

However, for some crystals, to ensure oscillation and accurate frequency generation, it is necessary

to add two small value external capacitors, C1 and C2. The exact values of C1 and C2 should be

selected in consultation with the crystal or resonator manufacturer┬ specification. The external

parallel feedback resistor, Rp, is required.

Some configuration options determine if the XT1/XT2 pins are used for the LXT oscillator or as I/O

pins.

● If the LXT oscillator is not used for any clock source, the XT1/XT2 pins can be used as

normal I/O pins.

● If the LXT oscillator is used for any clock source, the 32.768kHz crystal should be connected to

the XT1/XT2 pins.

To i nt er nal

ci rc ui ts

In te rn al

O sci ll at or

Ci rc ui t

No te :1 . Rp , C 1 and C 2 ar e re qui r ed.

2. A lt hough not s how n pi ns h av e a

par as it ic c apac it an ce o f ar ound 7pF .

In te r nal R C

O sc illa to r

32. 76 8

kH z

XT 1

XT 2

External LXT Oscillator

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