>I bought several of the OTP parts of the 12C509.  I am using Picstart Plus,
>with MPLAB-C 1.21.
>
>Its a simple program that I have run on many different chips, but this one
>just seems to sit there with no sign of pin change.
>
>The issues (as I understand them)
>
>        Set INTERNAL RC
>
>        Set Internal Reset
>
>       clear OPTION bit 5 and 6
>
>        use the __TRIS macro to set bit 0 and 1 as outputs
>
>       Whatelse is there?  I use the Pins a Output , but they never change.
>
>        Is there something I need to know about this internal clock?  What
>is the
>OSC Trim byte for?
>

You don't need to know anything about the OSCCAL value. If you do nothing
the chip will work, but not necessarily at 4MHz. On powerup, the chip
always executes a 'MOVLW' instruction, though, loading W with the
appropriate value for trimming the Osc. Your first instruction in your
program should always be 'MOVWF OSCCAL' when running with the internal RC.

        Jim