HT69F340 Datasheet, PDF (76/235 Pages) Holtek Semiconductor Inc – TinyPowerTM I/O Flash MCU with LCD & EEPROM

HT69F340/HT69F350/HT69F360
TinyPower^TM I/O Flash MCU with LCD & EEPROM
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 2¹⁸ 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 2¹⁸ division ratio, and a minimum timeout of 7.8ms for the 2⁸ division ration.
WDTC Register WE4~WE0 bits
RES pin reset
ʺHALTʺ instruction
ʺCLR WDTʺ instruction
LXT
LIRC
M
U
fSUB
fS
X
CLR
Reset MCU
8-stage Divider
fS/2⁸
WDT Prescaler
FSS bit
WS2~WS0
(fS/2⁸ ~ fS/2¹⁸)
Watchdog Timer
8-to-1 MUX
WDT Time-out
(2⁸/fS ~ 2¹⁸/fS)
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, situations may arise where it is necessary to forcefully apply a
reset condition when the microcontroller is running. One example of this is where after power has
been applied and the microcontroller is already running, the RES line is forcefully pulled low. In
such a case, known as a normal operation reset, some of the registers remain unchanged allowing
the microcontroller to proceed with normal operation after the reset line is allowed to return high.
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. Another reset exists in
the form of a Low Voltage Reset, LVR, where a full reset, similar to the RES reset is implemented in
situations where the power supply voltage falls below a certain threshold.
Reset Functions
There are several ways in which a microcontroller reset can occur, through events occurring both
internally and externally:
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.
Rev. 1.30
76
November 18, 2016