2.4.4 Initial_low, active_high Interrupt source If the PC0 is a initial_low, active_high signal, the interrupt service routine
should use INV0 to inverted/non-inverted the PC0 for high_pulse generation as
follows: (Refer to DEMO3.C)
Initial setting:
now_int_state=0; /* initial state for PC0 */
outportb(wBase+0x2a,1); /* select the non-inverted PC0 */
void interrupt irq_service()
{
if (now_int_state==1) /* now PC0 is changed to LOW */(c)
{ /* --> INT_CHAN_0=!PC0=HIGH now */
COUNT_L++; /* find a LOW_pulse (PC0) */
If((inport(wBase+7)&1)==0)/* the PC0 is still fixed in LOW */
{ /* Æ need to generate a high_pulse */
outportb(wBase+0x2a,1);/* INV0 select the non-inverted input */(d)
/* INT_CHAN_0=PC0=LOW --> */
/* INT_CHAN_0 generate a high_pulse */
now_int_state=0; /* now PC0=LOW */
}
else now_int_state=1; /* now PC0=HIGH */
/* don’t have to generate high_pulse */
}
else /* now PC0 is changed to HIGH */(a)
{ /* --> INT_CHAN_0=PC0=HIGH now */
COUNT_H++; /* find a High_pulse (PC0) */
If((inport(wBase+7)&1)==1)/* the PC0 is still fixed in HIGH */
{ /* need to generate a high_pulse */
outportb(wBase+0x2a,0);/* INV0 select the inverted input */(b)
/* INT_CHAN_0=!PC0=LOW --> */
/* INT_CHAN_0 generate a high_pulse */
now_int_state=1; /* now PC0=HIGH */
}
else now_int_state=0; /* now PC0=LOW */
/* don’t have to generate high_pulse */
}
if (wIrq>=8) outportb(A2_8259,0x20);
outportb(A1_8259,0x20);
}
PC0
INV0
INT_CHAN_0
(a) (b) (c) (d)