Selecting Oscillator speed?

[stokes]

How can I select a 16F84A to be in RC mode. All I can do is change the value for the extraction speed, how can I change the CONFIG registers to RC mode (stated in Datasheet of the device)

I have tried to use a 555 IC with variable resistors and cap's and hence I can't see the change in processor speed?

[Ettore]

How can I select a 16F84A to be in RC mode. All I can do is change the value for the extraction speed, how can I change the CONFIG registers to RC mode (stated in Datasheet of the device)

In MPASM you can set PIC's oscillator with the directive __CONFIG. You may have a look at MPLAB documentation.

I have tried to use a 555 IC with variable resistors and cap's and hence I can't see the change in processor speed?

This has been explained a lot of times in the old BBs. We are not definitely interested to simulate the oscillator features just to see CPU resources being spent only for this!

All CPUs have the property "Processor Clock Frequency"; use this in order to change clock. If you need any components (passive or actives) for LP mode just for PCB layout, then you may always include them, but I strongly suggest to exclude them from simulation (use relevant property in latest simulator version or PRIMITIVE=NULL in the older ones).