PIC16F877A to PC serial port using RS232.

Ajay, means i have to connect the collector pin of 2N3904 to pin 33 of PIC16 right? so i would remove VR1, LM324, and 74LS76?
cause since polling is done in software means the flip flops wont be of any use correct? the rest of the circuit is ok?

Yup that's right.

...

I am not sure how you are able to compile your code coz i found these errors by just seeing the code.. like

int i=o <<-- zero or o

a[]={63,6,91,79,102,109,125,7,127,,111};
before 111, you have put two commas. Please fix them and try running code again.

.

can you please explain what are you trying to do in this program, so will be easier to help out.

by configuring the 8051 as a negative edge triggered interrupt sensor i set IT1=1 and IT0=1 correct? then TCON=5 and IE=133. how do i write when the 8051 received interrupt from the sensor, it will display 1 on each increment of the interruption?

is it correct?

making ITx bit 1 will make your interrupts edge triggered, so whenever your signal goes high to low, you will get an interrupt.

to increment 1 at every interrupt you have to write an ISR (interrupt service routine). example

void INT0ISR() interrupt 0{
     //your increment code here for INT0
}

void INT1ISR() interrupt 2{
     //code for INT1
}

void INT0ISR() interrupt 0{
i++;
if (i>999) i=999;
P3_1=0;

for (m=0;m<=1000;m++);
P3_1=1;
}

void INT1ISR() interrupt 2{
i--;
if(i<0) i = 0;
P3_0=0;

for (m=0; m<=1000;m++);
P3_1=1;
}


The negative going pulse is applied when the persons interrupts the IR beam from TX2. It will trigger the INT0. The value of the counter increments by '1' when interrupt service routine for INT0 is executed right?