This behavior is common to the PICs with both internal RC
oscillator and internal MCLR pin options. In this case, the 
MCLR pin can be an input only pin if internal MCLR option is
used, but not an ouput pin.

Examples:  10F20x, 12F508/509, 16F505, 12F629/675/683/635, 
           16F630/676/684/688/636, 16F631/677/685/687/689/785, 
           PIC16F91x, etc

Recently Microchip is more careful about the description of
the I/O pins. For example, in the PIC16F785 datasheet, it is
written in Page 1 that it has "17 I/O pins and 1 input-only pin".

Regards,
Xiaofan

----------------------------------------------
Xiaofan Chen
R&D Engineer, Photoelectric Sensor Development
Pepperl+Fuchs Singapore
http://www.pepperl-fuchs.com
Signals for the world of automation
--------------------------------------------

-----Original Message-----
From: Michael Rigby-Jones 
Sent: Wednesday, August 03, 2005 3:17 PM
>
>I've been struggling to figure out why I can set GP1, GP2, GP4 
>and GP5 without trouble but I can't get GP3 to set. Set 
>meaning I can't get it to go high and turn on an LED. I'm 
>using a 12F675. I suspect it has something to do with my 
>config bits because MCLR is on GP3. Here's the simple program 
>I wrote. I'm hoping someone can help me spot my bug. Thanks.

The bug is that you didn't read page 22 of the datasheet!  GP3 is an input
pin only.

Regards

Mike
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