Hi all,

I want to count pulses from a rotary encoder who's output is 2 channel gray
code. I need to increment a counter when the encoder turns one way, and
decrement it when it turns the other way.

I want to handle the signals as fast as I can (so that I can support the
highest frequency of signal I can get away with). Numerous models of the
encoder are available, and the faster I can get the code, the better
resolution encoder I can use.

My test circuit has the two signals connected to RB0 and RB1, and i'm using
the INT0 and INT1 interrupts to detect the signal changes.

For now, i'm working in C on a PIC18f252. The final device I'll use i'm not
certain of yet but it will probably be one of the newer pic18 devices. But
that's not really very important at this stage.

I might consider reworking the code in assembler if there's a significant
gain to be had, but really at this stage i'm wondering if my *logic *is
correct, or could be improved.

Here's my code so far. Conceptually, are they any optimizations i'm missing=
?

if (INTCONbits.INT0IF) // INT0 & RB0 are encoder channel A
{
// change the edge we fire on
INTCON2bits.INTEDG0 =3D !PORTBbits.RB0;
 // clear the interrupt
INTCONbits.INT0IF=3D0;

if (PORTBbits.RB0 =3D=3D PORTBbits.RB1)
{
count++;
}
else
{
  count--;
}
}
else  if ( INTCON3bits.INT1IF ) // INT1 & RB1 are encoder channel B
{
// change the edge we fire on
INTCON2bits.INTEDG1 =3D !PORTBbits.RB1;
 // clear the interrupt flag
INTCON3bits.INT1IF=3D0;

if (PORTBbits.RB1 =3D=3D PORTBbits.RB0)
{
count--;
}
else
{
count++;
}
}

thanks
slip
--=20
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