HT48R063B datasheet(26/84 Pages) HOLTEK

26 / 84 page

HT48R063B/064B/065B/066B

Rev. 1.00

April 7, 2011

frequency of 4MHz within a tolerance of 2%. Here only

the OSC1 pin is used, which is shared with I/O pin PA6,

leaving pin PA5 free for use as a normal I/O pin.

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 Idle/Sleep 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 Power-down Mode. To do this,

another clock, independent of the system clock, must be

provided. To do this a configuration option exists to al-

low a high speed oscillator to be used in conjunction

with a a low speed oscillator, known as the LXT oscilla-

tor. The LXT oscillator is implemented using a 32768Hz

crystal connected to pins OSC1/OSC2. However, for

some crystals, to ensure oscillation and accurate fre-

quency 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. For

the devices 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.

32768 Hz Crystal Recommended Capacitor Values

· If the I/O option is selected then the XT1/XT2 pins can

be used as normal I/O pins.

· If the

²LXT oscillator²is selected then the 32kHz crys-

tal should be connected to the XT1/XT2 pins.

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.

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

P A 6 / O S C 1

4 7 0 p F

V D D

R O S C

P A 5 / O S C 2

External RC Oscillator

- ERC

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

HT48R063B Datasheet(PDF) 26 Page - Holtek Semiconductor Inc

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