BS85B12-3 HOLTEK [Holtek Semiconductor Inc], BS85B12-3 Datasheet - Page 46

• Manufacturer Part Number: BS85B12-3
• Description: Touch Key Flash Type 8-Bit MCU with LCD/LED Driver
• Manufacturer: HOLTEK [Holtek Semiconductor Inc]

Rev. 1.00
Wake-up
Programming Considerations
After the system enters the SLEEP or IDLE Mode, it can be woken up from one of various sources
listed as follows:
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.
Each pin on Port A can be setup using the PAWU register to permit a negative transition on the pin to
wake-up the system. When a Port A 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
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 or IDLE Mode, the wake-up function of the related interrupt will be disabled.
The high speed and low speed oscillators both use the same SST counter. For example, if the system is
woken up from the SLEEP Mode the HIRC oscillator needs to start-up from an off state.
HALT instruction. In this situation, the interrupt which woke-up the device will not be immediately
An external reset
An external falling edge on Port A
A system interrupt
A WDT overflow
If the device is woken up from the SLEEP Mode to the NORMAL Mode, the high speed system
oscillator needs an SST period. The device will execute the first instruction after HTO is high.
Oscillator
System
HIRC
LIRC
Touch Key Flash MCU with LCD/LED Driver
(SLEEP Mode)
Wake-up Time
15~16 HIRC cycles
1~2 LIRC cycles
Wake-Up Times
40
Wake-up Time
(IDLE0 Mode)
BS85B12-3/BS85C20-3
1~2 HIRC cycles
1~2 LIRC cycles
Wake-up Time
(IDLE1 Mode)
February 1, 2011