Oh, man, I cannot count the times I forgot about the watchdog timer and had
this problem.  There are a few gotchas that always hang projects, especially
at the beginning, and I've made them all:

1.  Watchdog enabled, but not reset in software

2.  Master CLear enabled, but not held high in hardware

3.  Port GP3, or RA4,  which is open collector in some PICs, has no pullup
resistor

4.  Port RB3, which is a low voltage programming input in some PICs, held
high which louses up ICSP programming

5.  TRIS registers not set to the right direction.

Write these 1000 times in the  EEprom blackboard. Paste these on your
forehead or your computer monitor with a yellow sticky note, then look at it
every time you program a PIC.  If you make one of these common mistakes,
whack the sticky note with your palm and chant with me: "D'Oh!"

--Lawrence

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