Wake up from power-down only once

Hello all,

I am working on a project using Winbond W77E58. To save energy, if there is no trigger input from P3.2 (INT0/), P3.3 (INT1/) or P3.0 (Serial Port) for some time the MCU will go into power-down mode. In my design, the MCU is woken by the external interrupt 3 (INT3/).

For the first time of power-down, the MCU can be woken by triggering the INT3/. But after some time when the MCU goes into power-down mode again, the MCU does not respond even though same input is from INT3/. It seems the MCU sleeps forever after the first awake.

unsigned char counter1=0x00;
unsigned char counter2=0x00;

void main(void)
{
unsigned short timer=0x0000;
while(1)
{
timer++;
if(timer=0x0F00)
{
PCON |= 0x02;//Power Down Mode
_nop()_;
timer=0x0000;
}//if
}//while
}//main

void interrupt_int0 (void) interrupt 0 using 1
{
counter1++;
}

void interrupt_int1 (void) interrupt 2 using 1
{
counter2++;
}

void interrupt_int3 (void) interrupt 8
{
}

Does anyone know how to solve this problem?

Please help.

Jones