Just to add to what others have said: there is actually no such thing, from what I've read, as a series crystal vs a parallel one. All crystals have both resonant modes. However, they are at two slightly different frequencies and the manufacturer has to choose one or the other to tune to the desired frequency. For example, a particular crystal might start out with a series resonant frequency of 9.900MHz and a parallel resonant frequency of 9.905MHz with no external capacitance. Let's say the manufacturer is trying to make a 10MHz crystal - they can shave off tiny bits of material or make some other kind of mechanical adjustment to shift the frequencies up or down but the two modes (series and parallel) will always be different so the manufacturer has to choose whether to tune the series mode to 10MHz or the parallel mode to 10MHz, and they also have to decide on a specific external capacitance to add (if parallel mode is intended) because that is how circuits which are intended to use the parallel mode typically work - that is, they add a few 10s of picofarads of external capacitance. Sean On Tue, Jan 17, 2012 at 1:11 PM, Nathan House wro= te: > I'm making a board for a PIC18 microcontroller and have a few > questions about crystal selection. Firstly, on Digi-Key, under the > heading "Load Capacitance," there is the option "Series" and then a > bunch of different capacitor options below that. Will a series crystal > work, or should I get one that uses capacitors? One other question I > have is regarding the crystal frequency. Most PIC18 microcontrollers > (all of the ones I've used, at least) have a PLL built in, so a > variety of different crystals can be used with the same resulting > system clock speed. If the PIC I'm using has a PLL that would allow me > to use, say, a 4MHz, 8MHz, 12MHz, 20MHz, or 24MHz crystal, is there > any reason to use a higher speed crystal as opposed to a lower speed > one? > > Appreciate your advice! > > Nathan > > -- > Student Hobbyist > www.roboticsguy.com > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .