Post by thread:[PIC]: Very Long timing delays

Hello, I have been experimenting with TMR0 and the prescaler to provide timing delays in my application. It seems pretty easy to do if you want short delays. However, when you are using a 4MHz clock, it seems to get difficult to get long delays, say like 1s. I can set the prescaler to 1:128 and start TMR0 at 0, and have the timer overflow every 32,768 cycles. At 4MHz, that's orders of magnitude away from a 1s delay, and I would like to have delays of 24 hrs or more! The only way I can think of getting around this is having the interrupt routine increment another register, and be able to count the cycles to a second that way. But again, that's a very inconvenient way if you want a routine to function every 24 hrs, you would need quite a lot of bits! I guess I have two other options, slowing the instruction clock down to the kilohertz range, or putting a secondary oscillator on T0CKI. If anyone has any advice to share, I'd be grateful to hear it. Thank You, -Mike -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

"Michael A. Powers" wrote: > > Hello, > > I have been experimenting with TMR0 and the prescaler to provide timing delays in my application. It seems pretty easy to do if you want short delays. However, when you are using a 4MHz clock, it seems to get difficult to get long delays, say like 1s. I can set the prescaler to 1:128 and start TMR0 at 0, and have the timer overflow every 32,768 cycles. At 4MHz, that's orders of magnitude away from a 1s delay, and I would like to have delays of 24 hrs or more! The only way I can think of getting around this is having the interrupt routine increment another register, and be able to count the cycles to a second that way. But again, that's a very inconvenient way if you want a routine to function every 24 hrs, you would need quite a lot of bits! I guess I have two other options, slowing the instruction clock down to the kilohertz range, or putting a secondary oscillator on T0CKI. If anyone has any advice to share, I'd be grateful to hear it. > > Thank You, > -Mike TMR0 can cycle every 65mS with the PS at 1:256 @4MHz That is roughly 15 counts per second and would need some trimming. There was some info about error free timing not long back. 86400 seconds in a day 15 X 86400 = 1296000 counts. 129600 = 13 C6 80 in HEX so you would need 3 registers. You could also 5 registers for these... 15 loop counter 1 second count - increments every 15 cycles 1 minute count - increments every 60 sec 1 hour count - increments every 60 min 1 day count - increments every 24 hour -- Best regards Tony mICros http://www.bubblesoftonline.com spam_OUTsalesTakeThisOuTbubblesoftonline.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>At 4MHz, that's orders of magnitude away from a 1s delay, and I would like >to have delays of 24 hrs or more! The only way I can think of getting >around this is having the interrupt routine increment another I guess you don't actually mean "delays," but "timers" of 24 hours or so. If you're really talking about delays, then you don't need interrupts - just set a loop for a given time and create the "delay." What you're describing is more of a "let-me-know-when-I've-reached-a-certain-time" timer. If you want something very long like this and need an accurate reference, why not just add a real-time clock chip and periodically read the current time off of it? If you want 24 hours, just check to see if the time values are equal. This would only require two I/O lines, clock and data. --Andrew _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Re: >I have been experimenting with TMR0 and the prescaler to provide >timing delays in my application. It seems pretty easy to do if you >want short delays. However, when you are using a 4MHz clock, it >seems to get difficult to get long delays, say like 1s. ... App Note AN-7 "Ninety-Day Countdown Timer" on our website may give you some ideas ... -- ______________________________________ Andrew E. Kalman, Ph.D. Salvo(TM), The RTOS that runs in tiny places(TM) Pumpkin, Inc. 750 Naples Street San Francisco, CA 94112 tel: (415) 584-6360 fax: (415) 585-7948 web: http://www.pumpkininc.com email: .....aekKILLspam@spam@pumpkininc.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Michael A. Powers wrote: > > Hello, > > I have been experimenting with TMR0 and the prescaler to provide timing delays in my > application. It seems pretty easy to do if you want short delays. However, when > you are using a 4MHz clock, it seems to get difficult to get long delays, say like > 1s. > At 4MHz, that's orders of magnitude away from a 1s delay, and I would like to have > delays of 24 hrs or more! Hi Michael, I have some sample code on my web page: http://centauri.ezy.net.au/~fastvid/one_sec.htm For giving easy, zero-error timing of 1 second with a 4MHz PIC or even much longer periods. The code uses very little ram, operates quick and can easily be inserted into whatever timer interrupts you may already be using with any frequency crystal. :o) -Roman -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

On Wed, 18 Jul 2001, Roman Black wrote: > Michael A. Powers wrote: > > > > Hello, > > > > I have been experimenting with TMR0 and the prescaler to provide timing delays in my > > application. It seems pretty easy to do if you want short delays. However, when > > you are using a 4MHz clock, it seems to get difficult to get long delays, say like > 1s. > > > At 4MHz, that's orders of magnitude away from a 1s delay, and I would like to have > > delays of 24 hrs or more! > > > Hi Michael, I have some sample code on my web page: > http://centauri.ezy.net.au/~fastvid/one_sec.htm I can vouch for this approach. I used a C implementation in a job I am just finishing up, and it's perfect. Bob Ammerman and Roman Black, I owe you each a beer or three. My clock now has NO drift other than whatever the crystal introduces -- I think we can live with 50PPM! 8-) Dale -- A train stops at a train station. A bus stops at a bus station. On my desk I have a workstation... -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

>> At 4MHz, that's orders of magnitude away from a 1s delay, and I would like to have delays of 24 hrs or more! The only way I can think of getting around this is having the interrupt routine increment another register, and be able to count the cycles to a second that way. But again, that's a very inconvenient way if you want a routine to function every 24 hrs, you would need quite a lot of bits! << Gimme a break! This is quite simple and is done all the time. The maximum timer 0 overflow rate is once every 65,536 instructions, or every 65.536mS at 4MHz oscillator. That is 15.26 times per second, so it only takes a 4 bit counter to get to a second. For 24 hours you need to count to 60 * 60 * 24 / 0.065536 = 1,318,359, which requires 21 bits, which requires only 3 bytes. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, olinKILLspamembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.