King Billion Electronics Co., Ltd.

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HE89C21

HE80000 SERIES

January 20, 2003

7

V1.0E

8. Oscillators

The MCU is equipped with two clock sources with a variety of selections on the types of oscillators to

choose from. So that system designer can select oscillator types based on the cost target, timing accuracy

requirements etc. With two clock sources available, the system can switch among operation modes of Fast,

Slow, Idle, and Sleep modes by the setting of OP1 and OP2 registers as shown in tables below to suit the

needs of application such as power saving, etc.

OP1

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Field

1

STOP

SLOW

INTE

T2E

T1E

Z

C

Mode

R

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Reset

1

0

0

0

0

0

-

-

OP2

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Field

IDLE

PNWK

TCWK

TBE

TBS[3..0]

Mode

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Reset

0

-

-

0

-

-

-

-

Crystal, Resonator or RC oscillator can be used as fast clock source. External components should be

placed as close to the oscillator pins as possible. The type of oscillator used is selected by mask option

MO_FXTAL.

MO_FXTAL Fast clock type

0

RC Oscillator.

1

Crystal Oscillator.

VDD

FXI

FXI

FXO

R

C

Slow clock is clock source for LCD display, Timer1, and Timer Base, etc. Crystal oscillator can be used

as slow clock. If used in feature phone applications, 32768 Hz crystal is suggested to generate DTMF

tone.