A crystal is just that. A canned oscillator contains a crystal and a oscillator circuit and a driver circuit. It drives out a nice clean full level clock signal and is a total no-brainer. The canned oscillator will save one the hassle of designing an oscillator and of course is more expensive than just a crystal. The PIC naturally has an oscillator circuit and driver included, however to connect a crystal you must also add some phase shift capacitors to get it to oscillate so it is still some effort on your part. See the data book for more info on connecting crystals. Basically, it boils down to a hassle vs. cost tradeoff. I don't have a databook with the canned oscillators, however from what I remember, if you fit it into a 14-pin socket, pin 7 is Vss, 14 is Vdd, 8 is OSCOUT, and 1 is N/C. The 4th unused (pin 1) pin keeps the thing from falling over when sitting on your desk! Rgds, Brian. ______________________________ Reply Separator _________________________________ Subject: Re: Using Oscillator w/ PIC Author: mgoelzer@us.net (Mike Goelzer) at Internet_Exchange Date: 11/27/95 5:54 PM >> I'm a bit embarassed to admit this, but all the PIC projects I've >>ever done have used RC oscillators. Now I want to get more accurate timing, >>so I ordered a 4.00Mhz oscillator from Mouser. It is a little metal package >>with four pins coming out. Can anyone tell me how to connect this thing >>to clock the PIC (I've never used a crystal before, as is probably plainly >>obvious)? > Sounds like you have a canned oscillator, not a Xtal. 2 of the 4 > leads should be Vdd/Vss and another is OSCOUT. Connect this line to > CLK1/OSCIN on the PIC and use XT mode for oscillator mode. You cannot > use RC mode. > > Rgds, Brian. Brian- Thanks for the info. Do you have any suggestions about how I could figure out which pins are Vdd,Vss and OSCOUT (e.g. are there known resistances I could measure with an ohmeter, or is there a standard, etc)? Also, if only three of the pins are used (Vdd,Vss and OSCOUT) why is there a forth pin on the package? Finally (sorry to ask so many questions), what's the difference betwen what I have ("a canned oscillator") and an "Xtal"? Is an Xtal better? Thanks for the info. I realize these are sort of basic questions, but I'm willing to bet there are at least a few others lurking on this list that would like to hear the answers. -mike -- Mike Goelzer