King Billion Electronics Co., Ltd.

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HE89C21

HE80000 SERIES

January 20, 2003

12

V1.0E

controls enable or disable of the circuit.

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

-

-

-

-

TBE Function

0

Disable Time Base

1

Enable Time Base

For example, if the slow clock is 32768 Hz, then the interrupt frequency is as shown in following table.

TBS[3..0] Interrupt Frequency

0000

16.384 KHz

0001

8.192 KHz

0010

4.096 KHz

0011

2.048 KHz

0100

1.024 KHz

0101

512 Hz

0110

256 Hz

0111

128 Hz

1000

64 Hz

1001

32 Hz

1010

16 Hz

1011

8 Hz

1100

4 Hz

1101

2 Hz

1110

1 Hz

1111

0.5 Hz

12. Watch Dog Timer

Watch Dog Timer (WDT) is designed to reset system automatically prevent system dead lock caused by

abnormal hardware activities or program execution. WDT needs to be enabled in Mask Option.

MO_WDTE Function

0

WDT disable

1

WDT enable

To use WDT function, “CLRWDT” instruction needs to be executed in every possible program path

when the program runs normally in order to clears the WDT counter before it overflows, so that the

program can operate normally. When abnormal conditions happen to cause the MCU to divert from

normal path, the WDT counter will not be cleared and reset signal will be generated.