Actually, Microchip says you MAY need the series resistor for AT cut crystals. And from what I can tell, you will need to get farads in there to keep the thing from oscillating. I may not have been clear before when I said to stuff a crystal in there. I meant between OSC1 and OSC2. It will almost always work. If you use a parallel cut crystal with a 20pF load spec (the most common type) and 20pF caps, the frequency is going to be very, very close to what is marked on the crystal. If you put some other value in there, it will only be very close. Like D Yates said, it only takes a little nudge. It's pretty tough to get very far wrong. The book may say 15-33 pF, but it works just fine with zero, and I'd be surprised if it didn't work with a 0.1u in there. It's terribly non-critical unless you are really hung up about getting the frequency spot on. I never did get the ceramic resonator thing. Microprocessor crystals are more stable, and no more expensive. The C-301 case jobs are also a lot smaller. The HC49 cases are a little larger but cheaper. But in all cases, we're talking under a buck (that's about 80% of a Euro these days), so it seems worth it to go for a little extra stability unless you're going to buy a thousand of the things. You can also stick an RC in there if you are more comfortable with that. Not as stable, nor as accurate, but you probably know how to calculate that. Like DY said, the oscillator is in there, it just needs a little poke. 72/73 de WB8RCR http://www.qsl.net/wb8rcr didileydadidah QRP-L #1446 Code Warriors #35 ----- Original Message ----- From: "D Yates" To: Sent: Wednesday, December 03, 2003 10:30 PM Subject: Re: [PIC:] Argh, more crystal questions. > > XTAL: > > GND ----------------------------------- > C1 = = C2 > | | > > | | > R1 | > | | > OSC1 OSC2 > || || > ------------------------------ > PIC > > 100 ohms < R1 < 1k > 10 pf < C1,2 < 50 pf > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads