PICAXE Timer
- Thread starter Groutie
- Start date
slimplynth
Senior Member
Hi Groutie... I guess it depends how accurate the timing needs to be, what are using it for? For my pir sensor I set a wait time of 40 seconds using...
replacing 4000 with 6000 would give you the 60 seconds(ish) you may require.
Code:
for b1 = 1 to 10
pause 4000
next b1
main: blah blah blahPIC AXE Timer
HI Simplynth
Thanks
I am mutlitasking 4 7seg displays as a clock so can't afford to use pauses etc as this affects the displays. I would to use the internal timers to generate the interrupt so that displays can be updated accurately
At present I am using nested loops to create the 1min delays but I think it's not that acuurate and I think using the internal clock etc would be better
Wot do you think?
Groutie
HI Simplynth
Thanks
I am mutlitasking 4 7seg displays as a clock so can't afford to use pauses etc as this affects the displays. I would to use the internal timers to generate the interrupt so that displays can be updated accurately
At present I am using nested loops to create the 1min delays but I think it's not that acuurate and I think using the internal clock etc would be better
Wot do you think?
Groutie
Jeremy Leach
Senior Member
Hi there
Yes, you need to use the SetTimer command, with an appropriate preload value, and the SetFlags command to set the interrupt. Look at SetTimer and SetFlags in the manual because it describes the detail. If you are using an external crystal then this will be very accurate.
Basically the internal timer has minor ticks and major ticks and the preload value sets the tick rate of the major ticks and how the Timer variable is incremented. When the timer variable overflows it can cause an interrupt (if you've setflags appropriately) and you can then update you 7seg displays in your interrupt routine.
Hope this gives you the general idea.
Yes, you need to use the SetTimer command, with an appropriate preload value, and the SetFlags command to set the interrupt. Look at SetTimer and SetFlags in the manual because it describes the detail. If you are using an external crystal then this will be very accurate.
Basically the internal timer has minor ticks and major ticks and the preload value sets the tick rate of the major ticks and how the Timer variable is incremented. When the timer variable overflows it can cause an interrupt (if you've setflags appropriately) and you can then update you 7seg displays in your interrupt routine.
Hope this gives you the general idea.
Groutie, check out this code snippet. It uses interrupts every second and should do what you are after with a bit of modification.
cheers, Arnie
For a clock, I would not recommend using the 28X1's internal timing (interrupt or other). It's only as accurate as the oscillator the 28X1 is running off, i.e. about 0.5 - 1%. A 1% error corresponds to about 15min per day! Better to use a dedicated real time clock chip (Dallas Semi / Maxim) running of a precise 32 kHz clock cystal. The Picaxe can then query the time from this chip a few times per second. Look at Rev-Ed's interfacing manual for details.
Wolfgang
Wolfgang
Jeremy Leach
Senior Member
True Womai, but an external crystal can also interface directly with the 28X1 and should be accurate. Surely?
True,a crystal is more accurate than a ceramic resonator. Although afaik those 32kHz crystals tend to be more accurate than generic multi-MHz crystals, because they are manufactured dedicated for precise timekeeping.
And the external RTC chip has the advantage that the Picaxe can go off and do other things without having to worry about keeping time - i.e. it frees up your interrupt for other things - and it takes care about leap years etc. in case you also want a date display.
And the external RTC chip has the advantage that the Picaxe can go off and do other things without having to worry about keeping time - i.e. it frees up your interrupt for other things - and it takes care about leap years etc. in case you also want a date display.