how to use encoder code?

[williamho]

Hi,
I am new in PIC and I am using 18F458 at 40MHz.
I need to capture optical encoder at 500 counts/rev at 1800 rpm.
I noticed that someone posted encoder code at below with remarks
that this code can gives a "maximum rotation rate of about 1800 rpm on 500 line encoder".

If this code can be used for my application, can anyone guide me how to put this code in main{} and how to printf it out?

Thanks.


signed int32 position;
#INT_RB
void quad(void) {
static int old;
static int new;
static int value;
//Here I have an edge on one of the quadrature inputs
new=portb;
/*Now I have to decode the quadrature changes. There are four
possibilities:
I can have a rising or falling edge, on each of the two inputs. I have to
look at the state of the other bit, and increment/decrement according to
this. /*
value=new^old;
//'value', now has the bit set, which has changed
if (value & 0x10) {
//Here the low bit has changed
if (new & 0x10) {
//Here a rising edge on A
if (new & 0x20) --position;
else ++position;
}
else {
//Here a falling edge on A
if (new & 0x20) ++position;
else --position;
}
}
else {
//Here the high bit (B) must have changed
if (new & 0x20) {
//Here a rising edge on B
if (new & 0x10) ++position;
else --position;
}
else {
//Here a falling edge on B
if (new & 0x10) --position;
else ++position;
}
}
old=new;
}

[Ttelmah]

The code must _not_ go in main.
It is interrupt driven, by the portB 'changed' interrupt. You need to connect the two encoder lines to port B4, and B5. Then in main, have: