BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 34

• Manufacturer Part Number: BS2824
• Description: Touch Key Mcu
• Manufacturer: Holtek Semiconductor Inc.

BS2824/BS2854/BS2868
Touch Key MCU
Rev. 1.00
Note:
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
resets the Program Counter and Stack Pointer, the other flags remain in their original status.
Pins PA0 to PA7 can be setup via the PAWK register to permit a negative transition on the pin to
wake-up the system. When a PA0 to 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 to 1 before entering the Idle/Sleep
Mode, then any future interrupt requests will not generate a wake-up function and 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.
1. t
2. t
3. t
4. t
HALT instruction. The TO flag is set if a WDT time-out occurs, and causes a wake-up that only
RSTD
RSTD
SST1
SST2
External RES
PA Port
Interrupt
WDT Overflow
Wake-up Source
= 2 or 1024 t
= 1024 t
(reset delay time), t
is power-on delay, typical time=100ms
SYS
Wake-up Delay Time
SYS
t
RSDT
ERC, IRC
SYS
t
SST1
+ t
Oscillator Type
(system clock)
SST1
34
t
RSDT
Crystal
t
SST2
+ t
SST2
January 27, 2010