PIC18F4850 will not oscillate
I have board that I can program using the U2 (USB) Programmer from melabs. I have a blink program that works well when I pick the internal oscillator (at 8Mhz). I have designed the card to use a 20MHz external oscillator but I have not been able to make it work. I just bought the programmer not too long ago, and I am able to program the device as long as I use the internal oscillator.
When I change the settings to HS on the meprog software, the board will not work and the oscillator will not oscillate (checked with a 10x probe). The design uses a 20Mhz oscillator (PN: ECS-200-20-5PXDU-TR, see attached schematic) and 20pF loading caps. The board layout is exactly as what has been recommended on the PIC datasheet. The only lines from the programmer to the card are GND, PGC, PGD, and my card has a 100K pull down on PGM. I have change the oscillator to another can oscillator I used on another circuit, but it still the new design does not work. During programming I am using the internal power supply which I checked an it is 4.98V. So I tried using the programmers Pin1 5V to power my board but that did not work either. I have also tried the @confiure..... but no luck neither.
I believe that somehow the fuses for external oscillator do not set properly and the oscillator does not oscillate. I have changed, oscillators, placed different loading caps, put a 1M across the oscillato, removed the laoding caps, but no luck so far. I am only able to run the board with internal OSC set up. I read on another thread that someone used the Vdd (Pin 4) on the USB programmer to power the board during programming and it worked. Nevertheless your website does explicitly said not to use the Vdd pin 4 as it is used for powering adaptors and not ICSP.
I would really appreciate if anyone can point me in the right direction, as I have tried everything and I have not been able to make the external oscillator to work. I believe I am having an issue with the programming of the HS fuse, but I just have not been able to make it work with the PIC18F4580. I am always setting up the HS with the programmer.
I have never had issues with oscillators not working, but somehow this one doesnt. By the way I have 2 board populated and they behave exactly the same, with and without the same oscillators.
Thank you,
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