HT56R656 datasheet(83/108 Pages) HOLTEK

83 / 108 page

HT56R62/HT56R65

HT56R642/HT56R644/HT56R654/HT56R656

Rev. 1.00

July 20, 2009

Internal 32K_INT Oscillator

When microcontrollers enter a power down condition,

their internal clocks are normally switched off to stop

microcontroller activity and to conserve power. How-

ever, in many microcontroller applications it may be nec-

essary to keep some internal functions operational,

such as timers, even when the microcontroller is in the

Power-down mode. To do this, the device has a

32K_INT oscillator, which is a fully integrated free run-

ning RC oscillator with a typical period of 31.2

msat5V,

requiring no external components. It is selected via con-

figuration option. When the device enters the Power

Down Mode, the system clock will stop running, how-

ever the 32K_INT oscillator will continue to run if se-

lected to keep various internal functions operational.

External 32768Hz Oscillator

With a function similar to the internal 32K-INT 32KHz os-

cillator, that is to keep some device functions opera-

tional during power down, this device also has an

external 32768Hz oscillator. This oscillator also remains

active at all times, even when the microcontroller is in

the Power-down mode. This clock source has a fixed

frequency of 32768Hz and requires a 32768Hz crystal

to be connected between pins OSC3 and OSC4.

The external resistor and capacitor components con-

nected to the 32768Hz crystal are not necessary to pro-

vide oscillation. For applications where precise

frequencies are essential, these components may be

required to provide frequency compensation due to dif-

ferent crystal manufacturing tolerances.

A configuration option selects whether the external

32768Hz oscillator or the internal 32K_INT oscillator is

selected. Selecting low frequency oscillators for use as

a system oscillator is implmented using bits in the

CLKMOD register.

During power-up there is a time delay associated with

the 32768Hz oscillator waiting for it to start-up. To mini-

mise this time delay, bit 4 of the RTCC register, known

as the QOSC bit, is provided to have a quick start-up

function. During a power-up condition, this bit will be

cleared to zero which will initiate the 32768Hz oscillator

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

power consumption associated with this quick start-up

function, to reduce power consumption after start-up

takes place, it is recommended that the application pro-

gram should set the QOSC bit high for about 2 seconds

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

condition the QOSC bit is set to, the 32768Hz oscillator

will always function normally, only there is more power

consumption associated with the quick start-up function.

32768Hz Oscillator C1 and C2 Values

Crystal Frequency

32768Hz

8pF

10pF

Note:

1. C3 and C4 values are for guidance only.

2. RP2=5M~10M

W is recommended.

32768 Hz Crystal Recommended Capacitor Values

External Oscillator

The system clock can also be supplied by an externally

supplied clock giving users a method of synchronising

their external hardware to the microcontroller operation.

This is selected using a configuration option and supply-

ing the clock on pin OSC1. Pin OSC2 should be left

floating if the external oscillator is used. The internal os-

cillator circuit contains a filter circuit to reduce the possi-

bility of erratic operation due to noise on the oscillator

pin, however as the filter circuit consumes a certain

amount of power, a oscillator configuration option exists

to turn this filter off. Not using the internal filter should be

considered in power sensitive applications and where

the externally supplied clock is of a high integrity and

supplied by a low impedance source.

O S C 4

O S C 3

C 4

C 3

R P 2

3 2 7 6 8 H z

External 32768Hz Oscillator

I n t e r n a l

3 2 K _ I N T

f R C 3 2 K

Internal 32K_INT Oscillator

HT56R656 数据表(PDF) 83 Page - Holtek Semiconductor Inc

HT56R656 数据表(HTML) 83 Page - Holtek Semiconductor Inc

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