Rev. 1.10
48
November 26, 2019
Rev. 1.10
49
November 26, 2019
HT68FB240
USB Low Speed Flash MCU
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 7.8ms for the 2
8
division ration.
“
CLR WDT
”
Instruction
8-stage Divider
WDT Prescaler
WE4~WE0 bits
WDTC Register
Reset MCU
f
SUB
f
SUB
/2
8
8-to-1 MUX
CLR
WS2~WS0
WDT Time-out
(2
8
/f
SUB
~2
18
/f
SUB
)
LIRC
“
HALT
”
Instruction
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. A hardware reset will of course
be automatically implemented after the device is powered on, however there is a number of other
hardware and software reset sources that can be implemented dynamically when the device is
running.
Reset Overview
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 instructions commence execution.
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.
The devices provide several reset sources to generate the internal reset signal, providing extended
MCU protection. The different types of resets are listed in the accompanying table.
Reset Name
Abbreviation Indication Bit Register
Notes
Power-On Reset
POR
—
—
Auto generated at power on
Reset Pin
RES
—
—
Hardware Reset
Low-Voltage Reset
LVR
LRF
CTRL
Low VDD voltage
Watchdog Reset
WDT
TO
STATUS
WDTC Register Setting
Software Reset
—
WRF
CTRL
Write to WDTC register
LVRC Register Setting
Software Reset
—
LRF
CTRL
Write to LVRC register
Reset Source Summary