HT48R01N datasheet(21/71 Pages) HOLTEK

21 / 71 page

HT46R01B/02B/01N/02N

HT48R01B/02B/01N/02N

Rev.1.10

February 12, 2010

Internal RC Oscillator

- HIRC

The internal RC oscillator is a fully integrated system os-

cillator 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 fre-

quency 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 degrees, the fixed oscilla-

tion frequency of 4MHz, 8MHz or 12MHz will have a tol-

erance within 2%. Note that if this internal system clock

option is selected, as it requires no external pins for its

operation, I/O pins PA5 and PA6 are free for use as nor-

mal I/O pins.

External 32768Hz Crystal Oscillator

- LXT

When the microcontroller enters the Sleep Mode, the

system clock is switched off to stop microcontroller ac-

tivity 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 Power-down Mode. To do this,

another clock, independent of the system clock, must be

provided. To do this a configuration option exists to allow

a high speed oscillator to be used in conjunction with a a

low speed oscillator, known as the LXT oscillator. The

LXT oscillator is implemented using a 32768Hz crystal

connected to pins OSC1/OSC2. However, for some

crystals, to ensure oscillation and accurate frequency

generation, it is necessary to add two small value exter-

nal 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. For the de-

vice the LXT oscillator must be used together with the

HIRC oscillator.

LXT Oscillator C1 and C2 Values

Crystal Frequency

32768Hz

8pF

10pF

Note:

1. C1 and C2 values are for guidance only.

2. RP=5M~10M

W is recommended.

32768Hz 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 CTRL0

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. How-

ever, 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 appli-

cation program sets the LXTLP bit high about 2 seconds

after power-on.

It should be noted that, no matter what condition the

LXTLP bit is set to, the LXT oscillator will always func-

tion normally, the only difference is that it will take more

time to start up if in the Low-power mode.

Internal Low Speed Oscillator

- LIRC

The LIRC is a fully self-contained free running on-chip

RC oscillator with a typical frequency of 13kHz at 5V re-

quiring no external components. When the device en-

ters the Sleep Mode, the system clock will stop running

but the WDT oscillator continues to free-run and to keep

the watchdog active. However, to preserve power in cer-

tain applications the LIRC can be disabled via a configu-

ration option.

P A 5 / P A 6 u s e d a s n o r m a l I / O s

N o t e :

I n t e r n a l R C

O s c i l l a t o r

P A 5 / O S C 2

P A 6 / O S C 1

Internal RC Oscillator

- HIRC

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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