The worst case error is always less than the amount of time per interrupt. btw: It wasn't Bob Blick's idea, but another Bob's :-) Bob Ammerman RAm Systems ----- Original Message ----- From: "Mccauley, Daniel H" To: Sent: Friday, April 11, 2003 10:54 AM Subject: Re: [PIC]:Accurate 1sec counter from system 4-20MHz clock??? > I realize this is "zero long term error", but what would be the error during > short durations. For example, what is the error per second for say a 5-10 > second duration. My application will require resolution to 0.001 sec for > about 5 to 10 seconds at which distance data will be plotted against time. > The actual "second period" created by my microcontroller only has to be > within +/- 1% of the actual scientific "Unit Second", but it has to be > accurate from second to second over that 5 to 10 seconds. > > Thanks > Dan > > > > > I just want to say that after reading Roman's page, I was > > thoroughly impressed > > with it!!! Good work Roman :-) > > > > Simple question though, and I think the answer is obvious. > > The "zero long term > > error" point is assuming the crystal (or whatever is used) > > doesn't vary over > > time and acts perfectly, correct? Or does this take that into account? > > > > Quoting Hazelwood Lyle : > > > > > >> Anyways, my PIC application will require an accurate 1 > > second internal > > > >> counter for timing, but does require a system clock > > speed of 4-20Mhz. > > > > > > > >Look in the archives for the thread, "[PIC]: simple > > one-second timer". > > > >Roman and Bob (Blick, I think it was) came up with a > > method I have used in > > > >numerous projects. I can post C code for my > > implementation of it, but > > > >that's in the archives too from a few months ago. > > > > > > I believe that Roman has also posted some of this on his website. > > > http://www.romanblack.com/one_sec.htm > > > > > > Lyle > > > > > > -- > > > http://www.piclist.com hint: To leave the PICList > > > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > > > > > > > > > > > > ---------------------------------------- > > This mail sent through www.mywaterloo.ca > > > > -- > > http://www.piclist.com hint: To leave the PICList > > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu