Rev. 1.60
80
August 20, 2019
Rev. 1.60
81
August 20, 2019
BS66F340/BS66F350/BS66F360/BS66F370
Touch A/D Flash MCU with LED Driver
BS66F340/BS66F350/BS66F360/BS66F370
Touch A/D Flash MCU with LED Driver
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 instruction. If the program malfunctions for whatever reason, jumps
to an unknown location, or enters an endless loop, the clear instruction will not be executed in the
correct manner, in which case the Watchdog Timer will overflow and reset the device. With regard to
the Watchdog Timer enable/disable function, there are five bits, WE4~WE0, in the WDTC register
to offer the enable/disable control and reset control of the Watchdog Timer. The WDT function will
be enabled when the WE4~WE0 bits are set to a value of 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. After power on these bits will have a value of 01010B.
WE4 ~ WE0 Bits
WDT Function
10101B or 01010B
Enable
Any other value
Reset MCU
Watchdog Timer Enable/Disable 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
reset, which means a certain value except 01010B and 10101B written into the WE4~WE0 field, the
second is using the Watchdog Timer software clear instruction and 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 contents.
The maximum time out period is when the 2
18
division ratio is selected. As an example, with a 32
kHz LIRC oscillator as its source clock, this will give a maximum watchdog period of around 8s for
the 2
18
division ratio and a minimum timeout of 7.8ms for the 2
8
division ration.
“
CLR WDT
”
Instruction
8-stage Divider
WDT Prescaler
WE4~WE0 bits
WDTC
Register
Reset MCU
LIRC
f
LIRC
f
LIRC
/2
8
8-to-1 MUX
CLR
WS2~WS0
(f
LIRC
/2
8
~ f
LIRC
/2
18
)
WDT Time-out
(2
8
/f
LIRC
~ 2
18
/f
LIRC
)
“
HALT
”
Instruction
Watchdog Timer