Mike Keitz wrote:

> A 10K resistor is way too small.  Use a 1M resistor to keep the
> current flow through the internal protection diodes low.  Then you
> probably won't need the external diode.   Of course, the 12C50X pin
> that doubles as MCLR (GP4?) can't be used this way since raising it
> above 5V will put the chip in programming mode.

> Install the resistor near the PIC so the high-impedance node between
> the resistor and PIC isn't affected by stray capacitance or noise.

  And put in a 10K resistor to ground as well to nominally terminate the
RS-232 line and snub noise.  On the source side, not the PIC!

  Cheers,
        Paul B.