HT56R67 datasheet(78/104 Pages) HOLTEK

78 / 104 page

HT56R67/HT56R668/HT56C668/HT56R678/HT56C678/HT56R688

Rev. 1.20

March 4, 2010

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.

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.

System Operating Modes

The devices have the ability to operate in several differ-

ent modes. This range of operating modes, known as

Normal Mode, Slow Mode, Idle Mode and Sleep Mode,

allow the devices to run using a wide range of different

slow and fast clock sources. The devices also possess

the ability to dynamically switch between different clocks

and operating modes. With this choice of operating

functions users are provided with the flexibility to ensure

they obtain optimal performance from the device ac-

cording to their application specific requirements.

Clock Sources

In discussing the system clocks for the devices, they

can be seen as having a dual clock mode. These dual

clocks are what are known as a High Oscillator and the

other as a divided frequency from high oscillator. The

High Oscillator and Low frequency are the system clock

sources and can be selected dynamically using the

HLCLK bit in the CLKMOD register.

The High Oscillator has the internal name fM whose

source is selected using a configuration option from a

choice of either an external crystal/resonator, external

RC oscillator or external clock source.

The Low frequency clock source, is further modified by

the SLOWC0~SLOWC2 bits in the CLKMOD register to

provide the low frequency clock source fSLOW.

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

HT56R67 Datasheet(PDF) 78 Page - Holtek Semiconductor Inc

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