"Oscillation" as such is not something that a PIC (usually) does when 
it has problems so the term is not one which is useful for PICs. It IS 
useful for eg voltage regulators. "Oscillation"  usually is taken to 
mean that the voltage (or current) at a circuit point is varying in a 
cyclical manner. Thus a PIC has an oscillator input and output which 
when properly connected DO exhibit "oscillations" which are used to 
drive the clock which controls the system's processing rate.

Oscillations are a problem when they occur when they shouldn't.  A 
voltage regulator such as the 7805 is meant to have a 5V output - if 
instead the output "oscillates" you have problems. Some voltage 
regulators are very prone to oscillating output levels if they do not 
have the correct specification capacitors connected. The 7805 is 
reasonably (but not totally)  immune to such things. Try connecting a 
10 uF from output to ground and another from input to ground close to 
the 7805 pins. This should not be strictly necessary but may help in 
practice. (I said 10 uF as this is a standard value but anything in 
the 1 uF to say 30 uF range should be OK.)(Even eg 100 uF should not 
hurt - too big on the output and you may get other issues but bot 
liable to be a problem here).

The 5.12 volt on the 5V rail sounds suspicious. It could be a high end 
of spec regulator or a poor meter but usually a 7805 will be closer 
than that.

If you have an oscilloscope you can check the 5v regulator output for 
oscillations. If not ...

Others have mentioned floating inputs and you have said that all spare 
pins are set to outputs so should be OK.



            RM

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