Rev. 1.00
40
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Rev. 1.00
41
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HT66FM5440
Brushless DC Motor A/D Flash MCU
HT66FM5440
Brushless DC Motor A/D Flash MCU
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 can be supplied by
the LIRC oscillator. 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 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.
Note that the Watchdog Timer function is always enabled, which can be controlled by the WDTC
register.
Watchdog Timer Control Register
A single register, WDTC, controls the required timeout period as well as the enable operation. The
WDTC register is initiated to 01010011B at any reset and keeps unchanged at the WDT time-out
occurrence in a power down state.
WDTC Register
Bit
7
6
5
4
3
2
1
0
Name
WE4
WE3
WE�
WE1
WE0
WS�
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
Bit 7~3
WE4~WE0
: WDT function software control
01010 or 10101: Enable
Other values: Reset MCU
When these bits are changed to any other values due to environmental noise the
microcontroller will be reset; this reset operation will be activated after 2~3 f
LIRC
clock
cycles and the WRF bit in the CTRL register will be set high.
Bit 2~0
WS2~WS0
: WDT time-out period selection
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.
CTRL Register
Bit
7
6
5
4
3
2
1
0
Name
FSYSON
—
—
—
—
LVRF
LRF
WRF
R/W
R/W
—
—
—
—
R/W
R/W
R/W
POR
0
—
—
—
—
x
0
0
"x": �nknown
Bit 7
FSYSON
: f
SYS
Control in IDLE Mode
Described elsewhere
Bit 6~3
Unimplemented, read as "0"