On Sat, 6 Dec 1997 18:01:16 -0600, you wrote:

>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?
Exactly that, i.e. to trim the oscillator to a nominal 4Mhz The first
instruction (at location 0) should be a MOVWF OSCCAL to load the
factory calculated value for the particular chip to the osccal
register. See earlier posts concerning erased cal values in JW parts. 

Even without this, programs should still run, albeit at the wrong
speed.
     ____                                                           ____
   _/ L_/  Mike Harrison / White Wing Logic / wwl@netcomuk.co.uk  _/ L_/
 _/ W_/  Hardware & Software design / PCB Design / Consultancy  _/ W_/
/_W_/  Industrial / Computer Peripherals / Hazardous Area      /_W_/