HT68F20 datasheet(43/210 Pages) HOLTEK

43 / 210 page

HT68F20/HT68F30/HT68F40/HT68F50/HT68F60

Rev. 1.00

November 3, 2009

Wake-up

After the system enters the SLEEP or IDLE Mode, it can

be woken up from one of various sources listed as fol-

lows:

· An external reset

· An external falling edge on Port A

· A system interrupt

· A WDT overflow

If the system is woken up by an external reset, the de-

vice 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 ac-

tual source of the wake-up can be determined by exam-

ining 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

²HALT²

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 regis-

ter to permit a negative transition on the pin to wake-up

the system. When a Port A pin wake-up occurs, the pro-

gram will resume execution at the instruction following

the

²HALT² 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

²HALT² 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 fi-

nally 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 inter-

rupt 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.

Programming Considerations

The HXT and LXT oscillators both use the same SST

counter. For example, if the system is woken up from the

SLEEP0 Mode and both the HXT and LXT oscillators

need to start-up from an off state. The LXT oscillator

uses the SST counter after HXT oscillator has finished

its SST period.

· If the device is woken up from the SLEEP0 Mode to

the NORMAL Mode, the high speed system oscillator

needs an SST period. The device will execute first in-

struction after HTO is

²1². At this time, the LXT oscilla-

tor may not be stability if fSUB is from LXT oscillator. The

same situation occurs in the power-on state. The LXT

oscillator is not ready yet when the first instruction is

executed.

· If the device is woken up from the SLEEP1 Mode to

NORMAL Mode, and the system clock source is from

HXT oscillator and FSTEN is

²1², the system clock can

be switched to the LXT or LIRC oscillator after wake

up.

· There are peripheral functions, such as WDT, TMs

and SIM, for which the fSYS is used. If the system clock

source is switched from fH to fL, the clock source to the

peripheral functions mentioned above will change ac-

cordingly.

· The on/off condition of f

SUB and fS depends upon

whether the WDT is enabled or disabled as the WDT

clock source is selected from fSUB.

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