Holtek HT46R003B Manual page 23

HT46R003B
Cost-Effective A/D 8-bit OTP MCU
If the system is woken up by an external reset, the device will experience a full system reset,
however, if the device is woken up by a WDT overflow, a Watchdog Timer reset will be initiated.
Although both of these wake-up methods will initiate a reset operation, the actual source of the
wake-up can be determined by examining the TO and PDF flags. The PDF flag is cleared by a
system power-up or executing the clear Watchdog Timer instructions and is set when executing the
"HALT" instruction. The TO flag is set if a WDT time-out occurs, and causes a wake-up that only
resets the Program Counter and Stack Pointer, the other flags remain in their original status.
Pins PA0~PA7 can be set via the PAWU register to permit a negative transition on the pin to wake-up
the system. When a PA0~PA7 pin wake-up occurs, the program will resume execution at the
instruction following the "HALT" instruction.
If the system is woken up by an interrupt, then two possible situations may occur. The first is where
the related interrupt is disabled or the interrupt is enabled but the stack is full, in which case the
program will resume execution at the instruction following the "HALT" instruction. In this situation,
the interrupt which woke-up the device will not be immediately serviced, but will rather be serviced
later when the related interrupt is finally enabled or when a stack level becomes free. The other
situation is where the related interrupt is enabled and the stack is not full, in which case the regular
interrupt response takes place. If an interrupt request flag is set high before entering the SLEEP
Mode, the wake-up function of the related interrupt will be ignored.
No matter what the source of the wake-up event is, once a wake-up event occurs, there will be a
time delay before normal program execution resumes. Consult the table for the related time
Note: 1. t
Rev. 1.00
Wake-up Source
External RES
PA Port
Interr�pt
WDT Overflow
(reset delay time), t (system clock)
RSTD SYS
2. t is power-on delay, typical time=50ms
RSTD
3. t =16t
SST SYS
Wake-up Delay Time
�3
Oscillator Type
HIRC, LIRC
t + t
RSTD SST
t
SST
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