I am experimenting with a PIC16F84A at the moment.
I can get this working fine using an RC network for the clock.
When I switch to using a crystal (the usual xtal across pins 15&16 with 2 caps going to ground from the same pins) I am not getting any clock at all.
The PIC is the 20MHz version, and I have tried all the crystals I have - 4MHz, 14.3MHz and 25MHz, and numerous different capacitors rangeing from 22pf right up into the uF range, but all I get is what appears to be a logic high on pin 15 and a logic low on pin 16.
Yes, I have changed the program config to be _XT_OSC (I have tried them all), but to no avail.
I am using gpasm to assemble the program and pk2cmd to flash the PIC in circuit under Ubuntu.
22pf 16 o----+---||----+ | | - | |=|Xtal +---+ - | | | | _ 15 o----+---||----+ - GND 22pf
(a little crude, I know ;) )