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
Bit 2
LVRF
: LVR function reset flag
Described elsewhere
Bit 1
LRF
: LVR control register software reset flag
Described elsewhere
Bit 0
WRF
: WDT control register software reset flag
0: Not occurred
1: Occurred
This bit is set to 1 by the WDT Control register software reset and cleared by the
application program. Note that this bit can only be cleared to 0 by the application program.
Watchdog Timer Operation
The Watchdog Timer operates by providing a device reset when its timer overflows. This means
that in the application program and during normal operation the user has to strategically clear the
Watchdog Timer before it overflows to prevent the Watchdog Timer from executing a reset. This is
done using the clear watchdog instructions. If the program malfunctions for whatever reason, jumps
to an unknown location, or enters an endless loop, these clear instructions will not be executed in the
correct manner, in which case the Watchdog Timer will overflow and reset the device. There are five
bits, WE4~WE0, in the WDTC register to offer the enable control and reset control of the Watchdog
Timer. The WDT function will be enabled if the WE4~WE0 bits are equal to 01010B or 10101B.
If the WE4~WE0 bits are set to any other values, other than 01010B and 10101B, it will reset the
device after 2~3 f
LIRC
clock cycles.
WE4~WE0 Bits
WDT Function
01010B or 10101B
Enable
Any other val�e
Reset MCU
Watchdog Timer Enable Control
Under normal program operation, a Watchdog Timer time-out will initialise a device reset and set
the status bit TO. However, if the system is in the SLEEP or IDLE Mode, when a Watchdog Timer
time-out occurs, the TO bit in the status register will be set and only the Program Counter and Stack
Pointer will be reset. Three methods can be adopted to clear the contents of the Watchdog Timer.
The first is a WDT software reset, which means a certain value except 01010B and 10101B written
into the WE4~WE0 bit
s
, the second is using the Watchdog Timer software clear instruction, the third
is via a HALT instruction.
There is only one method of using software instruction to clear the Watchdog Timer. That is to use
the single "CLR WDT" instruction to clear the WDT.
The maximum time-out period is when the 2
18
division ratio is selected. As an example, with a
32kHz LIRC oscillator as its source clock, this will give a maximum watchdog period of around 8
second for the 2
18
division ratio, and a minimum timeout of 8ms for the 2
8
division ration.
“
CLR WDT
”
Instr�ction
�-stage Divider
WDT Prescaler
WE4~WE0 bits
WDTC
Register
Reset MCU
LIRC
f
S
f
S
/�
�
�-to-1 MUX
CLR
WS�~WS0
WDT Time-o�t
(�
�
/f
S
~ �
1�
/f
S
)
“
HALT
”
Instr�ction
Watchdog Timer