Wouter van Ooijen wrote:

>> I have a PIC16F88 chip I'm trying to wire up on a breadboard to flash an
>> LED, running the internal RC oscillator.  I'm using the B Knudsen CC5X
>> compiler with MPLAB.  The Config word is 3FD0h.  I have WDT off, PWRT
>> on, MCLR off, BODEN on, LVP on, CPD off, Debuger off, and CCPMX is on.
> 
> IIRC the internal clock of this chip defaults to 32kHz.

- Fosc: INTRC, with port IO on RA6 and RA7

This selects one of the two internal oscillators. To set the actual
oscillator and frequency, you use OSCCON<4-6>. It defaults to 31.25kHz
<000>. However, running on the lower frequency might make your blinking
very slow, but shouldn't cause it to be erratic.

- MCLRE: Reset tied to Vdd, /MCLR/RA5 is port RA5

This ties the reset input internally to Vdd. May or may not be a good idea,
especially on a breadboard setup where you might "switch it on" by just
plugging in a wire. I don't have experience with this, so I can't tell
whether this works reliably on a breadboard. You could try a simple
resistor/capacitor reset circuit and set this bit to 1.

- LVP: enabled

As Alan said, as long as this is enabled, you need to pull RB3 low for
normal operation. Use a resistor (eg. 10k..100k) to pull it low.

A similar issue is with all the other IO pins. By default, they are all
inputs. If you have nothing connected to them, they are all floating
inputs. Which can cause funny things to happen. I recommend you make all
unconnected pins outputs. 

Also, as Scott said, make sure you have the recommended decoupling
capacitors near the PIC.

Gerhard

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