HT45F43 datasheet(38/152 Pages) HOLTEK

38 / 152 page

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

¢s 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.

LXT Oscillator C1 and C2 Values

Crystal Frequency

32.768kHz

10pF

Note:

1. C1 and C2 values are for guidance only.

2. RP=5M~10M

W is recommended.

32.768kHz Crystal Recommended Capacitor Values

LXT Oscillator Low Power Function

The LXT oscillator can function in one of two modes, the Quick Start Mode and the Low Power Mode.

The mode selection is executed using the LXTLP bit in the TBC register.

LXTLP Bit

LXT Mode

Quick Start

Low-power

After power on the LXTLP bit will be automatically cleared to zero ensuring that the LXT oscillator is

in the Quick Start operating mode. In the Quick Start Mode the LXT oscillator will power up and

stabilise quickly. However, after the LXT oscillator has fully powered up it can be placed into the

Low-power mode by setting the LXTLP bit high. The oscillator will continue to run but with reduced

current consumption, as the higher current consumption is only required during the LXT oscillator

start-up. In power sensitive applications, such as battery applications, where power consumption must

be kept to a minimum, it is therefore recommended that the application program sets the LXTLP bit

high about 2 seconds after power-on.

Rev. 1.20

September 15, 2011

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

T o i n t e r n a l

c i r c u i t s

I n t e r n a l

O s c i l l a t o r

C i r c u i t

C 1

C 2

R p

N o t e : 1 . R p , C 1 a n d C 2 a r e r e q u i r e d .

2 . A l t h o u g h n o t s h o w n p i n s h a v e a

p a r a s i t i c c a p a c i t a n c e o f a r o u n d 7 p F .

I n t e r n a l R C

O s c i l l a t o r

3 2 7 6 8 H z

External LXT Oscillator

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