Marty Robertson wrote: > A bit of a follow up... The unit had the right fuses set (HS). The design > for this circuit isn't new but the part (18F2520) and the layout are both > new. The oscillator circuit is straight from the data sheet with 100 ohm > series resistor (I've tried several values here). Before they had a similar > design using a 16F which hasn't had these problems. > > I was under the impression that using series instead of parallel cut > crystals by mistake would only change the frequency that it oscillated at, > not whether it oscillated at all. Is that a bad assumption? However, I'm > sure we have the right cut crystal because... > > I removed the crystal and ran a generator into the osc input, this worked > and the code ran. Also osc2 was showing the signal coming back out like I > would expect if the config was right. I put a 1M resistor across the > crystal and the oscillator started working at the right frequency. If it > works at all it is reliable, but ... this isn't a fix-all because a) I'm not > sure *why* this helped except a guess that the resistor in the feedback path > is helping the gate act like an amp (maybe someone here will know) and b) it > only works on 90% of the units, but for my purposes it let me get on with > the firmware. > > Anyway, I guess there are no specific questions but if anyone has anything > to add or has any good ideas here I'd love to hear about it. Thanks! > > I thought PICs needed Series crystals only. But normally, no 1M crystal is needed. > > > On 8/1/06, alan smith wrote: > >> The other question to ask is....have they worked in the past? Or is this a >> new design. Could be the crystal might be series cut instead of parallel >> cut? Wrong caps? >> >> But I'd go with Jan-Erik....do you have the chip configured for the right >> type of osc. >> >> Jan-Erik Soderholm wrote: >> Marty Robertson wrote : >> >> >>> My company just got in a >>> batch of boards with 18F2520's on them. >>> They seem to work fine with the internal >>> oscillator, but with the external oscillator there seems to >>> be no output. I checked with a scope and it is not oscillating. >>> >> What did you do to change the *config* of the PIC from >> INTOSC to LF or HS crystal osccilator ? >> >> >>> The crystal is connected exactly as suggested in the >>> datasheet. Where else can I look to find this problem? >>> >> Again, what was changed in the *config* ? >> >> Regards, >> Jan-Erik. >> >> >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >> >> >> --------------------------------- >> Do you Yahoo!? >> Get on board. You're invited to try the new Yahoo! Mail Beta. >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist