Hi there,
I am new to design with the PIC. I am about to present a class LED driving demo using a PIC 16F84. I recently ordered my parts but realised I forgot to order the 4Mhz clock oscillator. I don't have enough time (three days) to wait for a mail ordered oscillator. Can I use a 4 Mhz signal from a signal generator instead. Any other alternatives?
 
Coardially
Donald.
 
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Use a RC network fitted to tick at 100Khz (or 10, or 1 KHz), by example. Cheaper, easier, and because is a lot slower, you will spend less effort wasting time in empty nested loops to see the led blinking (I assume that you are not using the timer in a 'hello world' project). To locate the correct R and C values, take a look at the end of the 'F84 datasheet, there is a nice table there. And remember to burn the 'F84 with the osc in RC mode. If not, it will not work.
 
Hope it helps.