Rev. 1.10
74
October 23, 2020
Rev. 1.10
75
October 23, 2020
BC66F5652
2.4GHz RF Transceiver A/D Flash MCU
BC66F5652
2.4GHz RF Transceiver A/D Flash MCU
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 WDTC software reset, which means a certain value except 01010B and 10101B written
into the WE4~WE0 bit filed, 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.
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
seconds for the 2
18
division ratio, and a minimum timeout of 8ms for the 2
8
division ration.
“
CLR WDT
”
Instruction
WE4~WE0 bits
WDTC Register
Reset MCU
f
LIRC
CLR
“
HALT
”
Instruction
LIRC
8-stage Divider
WDT Prescaler
f
LIRC
/2
8
8-to-1 MUX
WS2~WS0
WDT Time-out
(2
8
/f
LIRC
~ 2
18
/f
LIRC
)
Watchdog Timer
Reset and Initialisation
A reset function is a fundamental part of any microcontroller ensuring that the device can be set
to some predetermined condition irrespective of outside parameters. The most important reset
condition is after power is first applied to the microcontroller. In this case, internal circuitry will
ensure that the microcontroller, after a short delay, will be in a well-defined state and ready to
execute the first program instruction. After this power-on reset, certain important internal registers
will be set to defined states before the program commences. One of these registers is the Program
Counter, which will be reset to zero forcing the microcontroller to begin program execution from the
lowest Program Memory address.
In addition to the power-on reset, another reset exists in the form of a Low Voltage Reset, LVR,
where a full reset is implemented in situations where the power supply voltage falls below a certain
threshold.
Another type of reset is when the Watchdog Timer overflows and resets the microcontroller. All
types of reset operations result in different register conditions being setup.
Reset Functions
There are several ways in which a microcontroller reset can occur, through events occurring
internally.
Power-on Reset
The most fundamental and unavoidable reset is the one that occurs after power is first applied to
the microcontroller. As well as ensuring that the Program Memory begins execution from the first
memory address, a power-on reset also ensures that certain other registers are preset to known
conditions. All the I/O port and port control registers will power up in a high condition ensuring that
all pins
will be first set to inputs.