----- Original Message ----- From: "Peter Restall" To: Sent: Saturday, October 17, 2009 5:20 AM Subject: [PIC] dsPIC30F Oscillator Requirements As far as i can tell, the PLL input is limited to 10 MHz, so a 20 MHz oscillator will get you a 20 MHz clock since you can't use the PLL, but a 5 MHz oscillator can get you an 80 MHz clock. > And a second question would be - where can I get 7.5MHz crystals from in > the > UK in small quantities (ie. 10) and at a reasonable price ? I've tried > Farnell, RS, Rapid, Digikey, eBay and Quarndon but can't see any; I can > pick > up 7.3728MHz ones easily, but you lose over 0.5 MIPS with those. Not > likely > to be a problem in my case I dare say, but still... If you want a 7.5 MHz crystal you need to get it custom made. These are expensive, although perhaps not as expensive as you might think. 7.3728 MHz crystals are a commodity item, and perhaps 1/20th to 1/50th the price of a custom crystal. My favorite crystal supplier is International Crystal, although there are others. International will take several weeks to make your crystal, and I'm guessing will cost somewhere around 15 pounds. You probably will not find a 7.5000 MHz crystal on the shelf, it will have to be made for you. There are other crystal manufacturers, some a little cheaper than International, but IMO International is very thorough and makes sure you get exactly what you need. One possible strategy is to use a programmable oscillator like those from Epson, although depending on your application, the phase noise can be a probem. These cost closer to 2 pounds, and can be delivered overnight. Still expensive compared to an off the shelf crystal which can be had here in the U.S. for as little as 27p. --McD -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist