Rev. 1.71
46
April 11, 2017
Rev. 1.71
47
April 11, 2017
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with 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 f
LIRC
clock which is supplied by the
LIRC oscillator. The Watchdog Timer source clock is then subdivided by a ratio of 2
8
to 2
1
5
to give
longer timeouts, the actual value being chosen using the WS2~WS0 bits in the WDTC register. The
LIRC internal oscillator has an approximate period of 32kHz at a supply voltage of 5V. However, it
should be noted that this specified internal clock period can vary with V
DD
, temperature and process
variations. The WDT can be enabled/disabled using the WDTC register.
Watchdog Timer Control Register
A single register, WDTC, controls the required timeout period as well as the enable/disable
operation. The WRF software reset flag will be indicated in the SMOD1 register. These registers
control 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
POR
0
1
0
1
0
0
1
1
B
it 7~ 3
WE4 ~ WE0
: WDT function software control
10101: WDT disable
01010: WDT enable
Other values: Reset MCU
When these bits are changed to any other values by the environmental noise to reset the
microcontroller, the reset operation will be activated after 2~3 LIRC clock cycles and the WRF
bit will be set to 1to indicate the reset source.
B
it 2~ 0
WS2 ~ WS0
: WDT Time-out
p
eriod selection
000: 2
8
/
f
LIRC
001: 2
9
/f
LIRC
010: 2
1
0
/f
LIRC
011: 2
11
/f
LIRC
(default)
100: 2
1
2
/f
LIRC
101: 2
13
/f
LIRC
110: 2
1
4
/f
LIRC
111: 2
1
5
/f
LIRC
These three bits determine the division ratio of the Watchdog Timer sourece clock, which in turn
determines the timeout period.