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Rev. 1.20
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Rev. 1.20
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HT69F30A/HT69F40A/HT69F50A
TinyPower
TM
I/O Flash 8-Bit MCU with LCD & EEPROM
HT69F30A/HT69F40A/HT69F50A
TinyPower
TM
I/O Flash 8-Bit MCU with LCD & EEPROM
Watchdog Timer
The Watchdog Timer is provided to prevent program malfunctions or sequences from jumping to
unknown locations, due to certain uncontrollable external events such as electrical noise.
Watchdog Timer Clock Source
The Watchdog Timer clock source is provided by the internal clock f
S
, which is in turn supplied by
the f
SUB
clock. The f
SUB
clock can be sourced from either the LXT or LIRC oscillator selected by a
configuration option. The LIRC internal oscillator has an approximate frequency of 32kHz and this
specified internal clock period can vary with V
DD
, temperature and process variations. The LXT
oscillator is supplied by an external 32.768kHz crystal. The Watchdog Timer source clock is then
subdivided by a ratio of 2
8
to 2
18
to give longer timeouts, the actual value being chosen using the
WS2~WS0 bits in the WDTC register.
Watchdog Timer Control Register
A single register, WDTC, controls the required time-out period as well as the enable/disable
operation. This register controls the overall operation of the Watchdog Timer.
WDTC Register
Bit
7
6
5
4
3
2
1
0
Name
WE4
WE3
WE2
WE1
WE0
WS2
WS1
WS0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
P�R
0
1
0
1
0
0
1
1
Bit 7~3
WE4~WE0:
WDT function enable control
If the WDT configuration option is “always enable”:
10101 or 01010: Enabled
Other Values: Reset MCU
If the WDT configuration option is “application program enable”:
10101: Disabled
01010: Enabled
Other Values: Reset MCU
If these bits are changed due to adverse environmental conditions, the microcontroller
will be reset. The reset operation will be activated after 2~3 LIRC clock cycles and the
WRF bit in the CTRL register will be set to 1.
Bit 2~0
WS2~WS0:
Select WDT Timeout Period
000: 2
8
/f
S
001: 2
10
/f
S
010: 2
12
/f
S
011: 2
14
/f
S
100: 2
15
/f
S
101: 2
16
/f
S
110: 2
17
/f
S
111: 2
18
/f
S
These three bits determine the division ratio of the Watchdog Timer source clock,
which in turn determines the timeout period.