Post by thread:40mhz clock for PIC18FXX2...

I just got my hands on an PIC18F252 to fiddle around with, and I want to clock it at 40mhz. On the PIC16's I am used to just throwing a 20mhz ceramic resonator w/caps on there, and being done with it....1 component...nice and simple. I couldn't find a 40mhz resonator to make this as simple an operation. So, what do most people do for a 40mhz, reliable, simple clock for these? The data sheet seems to suggest using a HS/PLL circuit to 4xstep-up a 10mhz crystal. This seems like overkill, and alot of additional circuitry...although would be nice without lots of EMI to mess things up. I have a couple of 20mhz crystals laying around I could double....but, keeping it simpler is sounding good to me. I really don't need the whole selectable clocking feature that using the PLL really buys. I am still quite the PIC newbie....so any suggestions would be greatly appreciated. Thanks, - Ted -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

> have a couple of 20mhz crystals laying around I could double....but, keeping > it simpler is sounding good to me. I really don't need the whole selectable > clocking feature that using the PLL really buys. Well, you could run it at 20MHz, or you could use the built-in PLL, like I've always done. To use a crystal all you need are a couple of small capacitors. I agree that a resonator is easier, and if you have some, use them. I've generally used a 10 MHz resonator with the built-in 4xPLL for 40 MHz. Good luck! -- D. Jay Newman ! Pudge controls the weather. .....jayKILLspam@spam@sprucegrove.com ! http://enerd.ws/~jay/ ! Oh good. My dog found the chainsaw. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Thanks for the quick reply. I am thinking that is what I am going to do...it is certainly the simplest method. Just plug it in, and enable the PLL I just didn't have a 10mhz resonator in my parts box. Thanks for the advice! - Ted {Original Message removed}

Ted Larson wrote... >So, what do most people do for a 40mhz, reliable, simple clock for these? Use a 10 MHz resonator and the HS/PLL clock option on the PIC. >The data sheet seems to suggest using a HS/PLL circuit to 4xstep-up a 10mhz >crystal. This seems like overkill, and alot of additional >circuitry...although would be nice without lots of EMI to mess things up. I >have a couple of 20mhz crystals laying around I could double....but, keeping >it simpler is sounding good to me. I really don't need the whole selectable >clocking feature that using the PLL really buys. What could be simpler? There's no "whole selectable clocking feature" involved here- it's a fixed, 4X frequency multiplication, and it's no harder to use than any of the other clock modes. Works great. Dave D. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

Try these Digi-Key p/n's: Surface mount 40MHz resonators PX400CTR-ND PX400JCT-ND PX400JTR-ND PX400CCT-ND Or, if you don't like surface mount and don't mind spending a little extra, do what I do and get yourself a 40MHz crystal oscillator. They are 1 part, 3 connections, can be a clock source for multiple chips (especially when you include a buffer) and provide a very robust temperature stable clock signal. {Original Message removed}

Brandon Tarr wrote... >Try these Digi-Key p/n's: > >Surface mount 40MHz resonators >PX400CTR-ND >PX400JCT-ND >PX400JTR-ND >PX400CCT-ND > >Or, if you don't like surface mount and don't mind spending a little extra, >do what I do and get yourself a 40MHz crystal oscillator. They are 1 part, >3 connections, can be a clock source for multiple chips (especially when you >include a buffer) and provide a very robust temperature stable clock signal. Note that while the data sheet lists the maximum input clock frequency from an external oscillator in the EC and ECIO modes as 40 MHz, the maximum frequency for a crystal or resonator in the HS mode is only 25 MHz. The PIC's on-chip oscillator may work at frequencies higher than that, it isn't guaranteed to. For a hobby project, using a 40 MHz resonator might work; but if you're trying to make a manufacturable product, it's not a good idea. Dave D. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body