Elapsed Timer Demo

[CocaColaKid]

Darrel,

I'm trying this code on an 877 and it work great, nice job. I would however like to run it on a 452 or a 4620. What would I have to change for this? I was looking thought the files and came across the lines:

  IF OSC == 4                       ; Constants for 100hz interrupt from Timer1
TimerConst = 0D8F7h                 ; Executed at compile time only
  EndIF
  If OSC == 8
TimerConst = 0B1E7h
  EndIF
  If OSC == 10
TimerConst = 09E5Fh
  EndIF
  If OSC == 20
TimerConst = 03CB7h
  EndIF

What would these be if I wanted to say run a PLL at 4 MHz or a PLL at 10 MHz?

[Darrel Taylor]

The easiest way to figure out the constant at any OSC is to use the Timer Calc form at ...
http://www.picbasic.co.uk/forum/showthread.php?t=2031

For instance, in the form, enter 4 in the OSC field, then put 100 in the bottom Freq field. Press Calculate, and it shows that it takes 10,000 "Ticks" of the timer. And the number to reload into the Timer on each interrupt is 55543, or 0D8F7h This is the same number shown in the ASM section you listed, for 4Mhz.

That's 65536 - 10000 + 7

7 is the number of instructions used to reload the timer. (Elapsed.bas : ADD2_TIMER)

So, just plug in the new OSC value (Any crystal or PLL Freq) and enter 100 in the FREQ field. The new constant can be added to the ASM section of Elapsed.bas.

Also, I have a version of "Elapsed" for the 18F's. I'll send it, later tonight, when I get off work.

L8R,
Darrel

[Darrel Taylor]

Here's the version for 18F's.

It should be a drop-in replacement for the old version. Everything works the same, except for the registers saved on entry to the INT routine.

So, you can still use the Test_Elapsed_LCD/SER.bas demo's from the original version for testing. Just add the "-18" to the INCLUDE line.
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[CocaColaKid]

It works like a charm, thank you vary much. Now I can finish making my waterbed temperature controller.

[crematory]

Hi Darrel

I was wondering if elapsed timer code is accurate enough to make a digital clock and calender, showing time and date.

Thanks

[Darrel Taylor]

Hi crematory,

That depends on the accuracy of the crystal being used, and the ambient temperature.
And, you'd probably need to have some kind of backup battery, to keep it going during any power outages.

I think I calculated it at around +/- 4 minutes per year with a standard 20mhz crystal. It was around 20 seconds/year with one of those temperature compensated TTL Oscillators.
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[crematory]

Hi crematory,

That depends on the accuracy of the crystal being used, and the ambient temperature.
And, you'd probably need to have some kind of backup battery, to keep it going during any power outages.

I think I calculated it at around +/- 4 minutes per year with a standard 20mhz crystal. It was around 20 seconds/year with one of those temperature compensated TTL Oscillators.
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4 Minutes a year, that is more than acceptable for me, I will be happy with that in deed.

I was wondering if you can through a hint for using the rest of interrupts in the PIC when using the elapsed timer code, shall I use your way to handle other interrupts, or what should I exactly do.

Thanks Darrel

[sayzer]

Hi crematory,

That depends on the accuracy of the crystal being used, and the ambient temperature.
And, you'd probably need to have some kind of backup battery, to keep it going during any power outages.

I think I calculated it at around +/- 4 minutes per year with a standard 20mhz crystal. It was around 20 seconds/year with one of those temperature compensated TTL Oscillators.
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Hi Darrel,

Could you suggest a good "one of those temperature compensated TTL Oscillators" please ?

Also, if aging for an oscillator is stated, say, +/-5ppm a year or +/- 100ppm a year, what would it mean in your elapsed timer application?

Last question, if I modify your routine to work for 100years, forget about power failures etc., and use a good osc as you may suggest, what would be a possible problem as years pass by?

Thanks.


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[jessey]

Here's the version for 18F's.

It should be a drop-in replacement for the old version. Everything works the same, except for the registers saved on entry to the INT routine.
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Hello Darrel,

I tried using your Elapsed-18 for use with my 18f452 and when I compile I get these errors:

Error(113)c\pbp\10tim~2asm 503:Symbol not previously defined (TimerConst)
Error(113)c\pbp\10tim~2asm 507:Symbol not previously defined (TimerConst)

Would you have any ideas why I'm getting these errors or what I could try to get it to compile? I got my new version of PBP 2.47 installed now.

Thanks
jessey

[Darrel Taylor]

Hi Jessey,

What OSC are you using?

The Elapsed-18.bas only has constants for 4,8,10,20 and 40 mhz.

If it's something different, it needs a new constant.
See Post #17
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[jessey]

What OSC are you using?
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Hi Darrel,

I was running my pic at 16 mhz, I changed it to 4 and its working great now.

Thanks A Lot
jessey