=20
I wanted to hopefully caution someone against making the same mistake I
made.  In the interest of reducing part count, I have been working on
using a 16F628 to do modulated (38 Khz) IR.  I wanted to have everything
on one chip, instead of having to use multiple chips.  I did the
modulation and bit-banging myself, for 1200 baud IR communication.  I
was using the internal oscillator of the 16F628.  Basically, I could get
it working fine, and then I would come back the next morning, and it
would be slightly off, missing a few bits on certain values, while
working fine on others.  I messed with this for two days, trying to
tweak things to make them work correctly.  It was very frustrating.
And then i though about the temperature variations, and the internal
clock.  Arggh!  I added a ceramic resonator, and everything worked
flawlessly.
=20
I though that the internal clock would have been accurate enough for
something as coarse as 1200 baud serial, but apparently it is not.
=20
I've attached the source code for the IR function below, in case anyone
is interested.  I am using the CCS compiler, and a 4 MHz clock.  The
16/4 loop makes a 38 KHz pulse. =20
=20
Alex
=20
void IRWrite(byte b)
{
=20
   disable_interrupts(INT_EXT);
=20
   #use fast_io(b)

     // start bit
      for(i=3D0;i<27;i++)
      {
         output_low(PIN_B2);
         delay_us(16);
         output_high(PIN_B2);
         delay_us(4);
      }
=20
   // serials
=20
   for(j=3D0; j<8;j++)
   {
=20
      if(!shift_right(&b,1,0))
      {
         // output a modulated zero
         for(i=3D0;i<27;i++)
         {
            output_low(PIN_B2);
            delay_us(16);
            output_high(PIN_B2);
            delay_us(4);
         }
=20
      }
      else // output a one
      {
         output_high(PIN_B2);
         delay_us(760);
=20
      }
=20
   }
=20
   // stop bit
   output_high(PIN_B2);
   delay_us(760);
   #use standard_io(b)
   enable_interrupts(INT_EXT);
}

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