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HT46R003B
Cost-Effective A/D 8-bit OTP MCU
HT46R003B
Cost-Effective A/D 8-bit OTP MCU
Watchdog Timer
The Watchdog Timer, also known as the WDT, 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 LIRC oscillator, the system clock f
SYS
and
its division clock f
SYS
/4, which
are
sourced from the HIRC oscillator. The Watchdog Timer source
clock is then subdivided by a ratio of 2
8
to 2
15
to give longer timeouts, the actual value being chosen
using the WS2~WS0 bits in the WDTS register. The LIRC internal oscillator has an approximate
period frequency of 12kHz 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.
Watchdog Timer Control Registers
WDTS Register
Bit
7
6
5
4
3
2
1
0
Name
—
—
—
—
—
WS�
WS1
WS0
R/W
—
—
—
—
—
R/W
R/W
R/W
POR
—
—
—
—
—
1
1
1
Bit 7~3
Unimplemented, read as “0”
Bit 2~0
WS2~WS0
: WDT Time-out period selection
000: 2
8
/f
S
001: 2
8
/f
S
010: 2
10
/f
S
011: 2
11
/f
S
100: 2
12
/f
S
101: 2
13
/f
S
110: 2
14
/f
S
111: 2
15
/f
S
These three bits determine the division ratio of the Watchdog Timer source clock,
which in turn determines the timeout period.
WDTC Register
Bit
7
6
5
4
3
2
1
0
Name WDTCLS1 WDTCLS0 WDTEN5 WDTEN� WDTEN3 WDTEN� WDTEN1 WDTEN0
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
POR
0
0
0
0
0
0
0
0
Bit 7~6
WDTCLS1~WDTCLS0
: WDT/Timer/PWM/Time base clock source
00: f
LIRC
01: f
SYS
/4
10: f
SYS
11: f
SYS
Bit 5~0
WDTEN5~WDTEN0
: WDT enable control
000000: Enable
101101: Disable
Other values: MCU reset
When these bits are changed by the environmental noise to reset the microcontroller,
the reset operation will be activated after 2~3 LIRC clock cycles.