Rev. 1.71
48
April 11, 2017
Rev. 1.71
49
April 11, 2017
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
The maximum time-out period is when the 2
1
5
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
1
second for the 2
1
5
division ratio, and a minimum timeout of 7.8ms for the 2
8
division ration.
“
CLR WDT
”
Instruction
11-stage Divider
7-stage Divider
WE4~WE0 bits
WDTC Register
Reset MCU
LIRC
f
LIRC
8-to-1 MUX
CLR
WS2~WS0
(f
LIRC
/2
1
~ f
LIRC
/2
11
)
WDT Time-out
(2
8
/f
LIRC
~ 2
15
/f
LIRC
)
RES pin reset
“
HALT
”
Instruction
Watchdog Timer
Reset and Initialisation
A reset function is a fundamental part of any microcontroller ensuring that the devices 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 microcontroller 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 is implemented in situations where the power
supply voltage falls below a certain threshold.