HT46R01 datasheet(41/60 Pages) HOLTEK

41 / 60 page

HT46R01/HT46R02/HT46R03

Rev. 1.00

September 21, 2007

Oscillator

Various oscillator options offer the user a wide range of

functions according to their various application require-

ments. Four types of system clocks can be selected

while various clock source options for the Watchdog

Timer are provided for maximum flexibility. All oscillator

options are selected through the configuration options.

System Clock Configurations

There are four methods of generating the system clock,

using an external crystal/ceramic oscillator, an external

RC network, an internal RC clock source and a com-

bined internal RC clock source and Real Time Clock.

One of these four methods must be selected using the

configuration options.

System Crystal/Ceramic Oscillator

After selecting the correct oscillator configuration op-

tion, for most crystal oscillator configurations, the simple

connection of a crystal across OSC1 and OSC2 will cre-

ate the necessary phase shift and feedback for oscilla-

tion, without requiring external capacitors. However, for

some crystal types and frequencies, to ensure oscilla-

tion, it may be necessary to add two small value capaci-

tors, C1 and C2. Using a ceramic resonator will usually

require two small value capacitors, C1 and C2, to be

connected as shown for oscillation to occur. The values

of C1 and C2 should be selected in consultation with the

crystal or resonator manufacturer

¢s specification. In

most applications, resistor R1 is not required, however

for those applications where the LVR function is not

used, R1 may be necessary to ensure the oscillator

stops running when VDD falls below its operating range.

More information regarding the oscillator is located in

Application Note HA0075E on the Holtek website.

External System RC Oscillator

After selecting the correct configuration option, using

the external system RC oscillator requires that a resis-

tor, with a value between 24k

W and 1.5MW,iscon-

nected between OSC1 and VDD, and a 470pF capacitor

is connected to ground. Although this is a cost effective

oscillator configuration, the oscillation frequency can

vary with VDD, temperature and process variations and

is therefore not suitable for applications where timing is

critical or where accurate oscillator frequencies are re-

quired. For the value of the external resistor ROSC refer

to the Appendix section for typical RC Oscillator vs.

Temperature and VDD characteristics graphics. Note

that 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 System RC Oscillator

In addition to the external crystal/resonator or external

RC system clock configurations, the devices also in-

clude an internal RC oscillator. The internal 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 device used. This

oscillator is fully integrated within the microcontroller

and requires no external components. 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.

Internal System RC Oscillator with RTC

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 an 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. Additionally a

10pf capacitor should be connected between OSC1 and

ground.

O S C 2

O S C 1

C 2

C 1

R 1

Crystal/Ceramic Oscillator

O S C 1

O S C 2

f S Y S / 4 N M O S O p e n D r a i n

4 7 0 p F

V D D

R O S C

RC Oscillator

· I n t e r n a l R C S y s t e m O s c i l l a t o r

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

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

HT46R01 Datasheet(PDF) 41 Page - Holtek Semiconductor Inc

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