BS84B06A-3 Datasheet, PDF (47/119 Pages) Holtek Semiconductor Inc – Touch A/D Flash MCU

BS84B06A-3
Touch A/D Flash MCU
WDTC
Register
WE4~WE0 bits
“HALT”Instruction
“CLR WDT”Instruction
LIRC
f_SUB
CLR
Reset MCU
f_S/2⁸
8-stage Divider
WDT Prescaler
WS2~WS0
(f_SUB/2⁸ ~ f_SUB/2¹⁸)
Watchdog Timer
8-to-1 MUX
WDT Time-out
(2⁸/f_SUB ~ 2¹⁸/f_SUB)
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.
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.
Reset Functions
There are four 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.
VDD
Power-on
Reset
SST Time-out
t_RSTD
Power-On Reset Timing Chart
Rev. 1.30
47
June 30, 2016