HT46R01A datasheet(37/58 Pages) HOLTEK

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HT46R01A

Rev. 1.10

August 13, 2008

Internal RC Oscillator

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, the choice of which is indicated

by the suffix marking next to the part number of the de-

vice used. 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 normal I/O

pins. Refer to the Appendix section for more information

on the actual internal oscillator frequency vs. Tempera-

ture and VDD characteristics graphics.

Internal RC Oscillator + External RTC Oscillator

When the microcontroller enters the Power Down 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 allow

the Internal System RC Oscillator to be used in conjunc-

tion with a Real Time Clock - RTC oscillator. Here the

OSC1 and OSC2 pins, which are shared with I/O pins

PA6 and PA5 should be connected to a 32768Hz crystal

to implement this internal RTC oscillator. However, for

some crystals, to ensure oscillation and accurate fre-

quency generation, it may be 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 specifica-

tion. The external parallel feedback resistor, Rp, is nor-

mally not required but in some cases may be needed to

assist with oscillation start up.

Internal Ca, Cb, Rf Typical Values @ 5V, 25

°C

11~13pF

13~15pF

270k

RTC Oscillator Internal Component Values

RTC Oscillator C1 and C2 Values

Crystal Frequency

32768Hz

TBD

Note:

1. C1 and C2 values are for guidance only.

2. CL is the crystal manufacturer specified

load capacitor value.

32768 Hz Crystal Recommended Capacitor Values

For applications using the RTC oscillator, the system

clock can be chosen to be either the Internal System RC

Oscillator or the RTC oscillator itself. This selection is

made using the CLKMOD bit in the CTRL0 register. If

this bit is set high then the 32768Hz external crystal will

also provide the system clock source. If the bit is low

then the system clock source will be the Internal RC Os-

cillator. When the system enters the Power Down Mode,

the system clock, irrespective of whether the CLKMOD

bit has selected the RTC or Internal RC Oscillator as its

source, will always stop running. The accompanying ta-

ble shows the relationship between the CLKMOD bit

and the various oscillators.

Operating

Mode

CLKMOD

Bit

Internal

RC Osc.

RTC

System

Clock

Normal

Running

0On

Oscillator

Off

32768Hz

Power

Down

Off

Stopped

During power up there is a time delay associated with

the RTC oscillator waiting for it to start up. Bit 1 of the

CTRL0 register, known as the QOSC bit, is provided to

give a quick start-up function and can be used to mini-

mize this delay. During a power up condition, this bit will

be cleared to 0 which will initiate the RTC oscillator quick

start-up function. However, as there is additional power

consumption associated with this quick start-up func-

tion, to reduce power consumption after start up takes

place, it is recommended that the application program

should set the QOSC bit high about 2 seconds after

power on. It should be noted that, no matter what condi-

tion the QOSC bit is set to, the RTC oscillator will always

function normally, only there is more power consump-

tion associated with the quick start-up function.

O S C 1

O S C 2

R f

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

C a

C b

R p

N o t e : 1 . R p i s n o r m a l l y n o t 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 O S C 1 / O S C 2 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

Internal RC Oscillator + External RTC Oscillator

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

P A 6

Internal RC Oscillator

HT46R01A Datasheet(PDF) 37 Page - Holtek Semiconductor Inc

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