HT46F46E datasheet(53/88 Pages) HOLTEK

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HT46F46E/HT46F47E/HT46F48E/HT46F49E

Rev. 1.40

July 28, 2009

Oscillator

Various oscillator options offer the user a wide range of

functions according to their various application require-

ments. Two 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.

The two methods of generating the system clock are:

· External crystal/resonator oscillator

· External RC oscillator

One of these two methods must be selected using the

configuration options.

More information regarding the oscillator is located in

Application Note HA0075E on the Holtek website.

External Crystal/Resonator Oscillator

The simple connection of a crystal across OSC1 and

OSC2 will create the necessary phase shift and feed-

back for oscillation, and will normally not require exter-

nal capacitors. However, for some crystals and most

resonator types, 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

470k

Oscillator Internal Component Values

Crystal Oscillator C1 and C2 Values

Crystal Frequency

8MHz

TBD

4MHz

TBD

1MHz

TBD

Note:

1. C1 and C2 values are for guidance only.

2. CL is the crystal manufacturer specified

load capacitor value.

Crystal Recommended Capacitor Values

Resonator C1 and C2 Values

Resonator Frequency

3.58MHz

TBD

1MHz

TBD

455kHz

TBD

Note:

C1 and C2 values are for guidance only.

Resonator Recommended Capacitor Values

External RC Oscillator

Using the external system RC oscillator requires that a

resistor, with a value between 15k

W and 750KW,iscon-

nected between OSC1 and VDD, and a capacitor is con-

nected to ground. The generated system clock divided by

4 will be provided on OSC2 as an output which can be

used for external synchronization purposes. Note that as

the OSC2 output is an NMOS open-drain type, a pull high

resistor should be connected if it to be used to monitor the

internal frequency. Although this is a cost effective oscil-

lator configuration, the oscillation frequency can vary with

VDD, temperature and process variations and is there-

fore not suitable for applications where timing is critical or

where accurate oscillator frequencies are required.For

the value of the external resistor ROSC refer to the Holtek

website for typical RC Oscillator vs. Temperature and

VDD characteristics graphics. Note that it is the only

microcontroller internal circuitry together with the external

resistor, that determine the frequency of the oscillator.

The external capacitor shown on the diagram does not

influence the frequency of oscillation.

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

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 .

Crystal/Resonator Oscillator

HT46F46E Datasheet(PDF) 53 Page - Holtek Semiconductor Inc

HT46F46E Datasheet(HTML) 53 Page - Holtek Semiconductor Inc

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