Performing a loop every 10ms
Hello. I am not sure how to setup my PIC16F877A to run a looping section of my code every 10ms. A rate gyro must be read every 10ms consistently so that my integeration calculations don't go crazy. I've read the Timer0 section of the datasheet but I just don't understand it well enough to achieve what I want. I am using PIC Basic PRO.
If I have missed an important piece of information here please ask me for it.
Thankyou.
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needed
Can you display your code so that I will have an idea on what's going on.
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Hi, Wassup
As Timer 0 is a 8 bits timer ... and we suppose clock is 4Mhz ( ... )
I will be necessary to have a counting loop in the interrupt stub , because interrupts will occur every 256 µs as a maximum
The other solution is to use Timer 1 that has a 16 bits counting range ... and won't need any calculations.
Have a SEARCH for "PicMultiCalc" from Mr E. it's a nice tool to help for Timer designs ...
Alain
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Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
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IF there is the word "Problem" in your question ...
certainly the answer is " RTFM " or " RTFDataSheet " !!!
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??Originally Posted by Acetronics
Minimum?
Maximum?
I must be on the other side of the mirror.
"If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte
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The other side of the Bosphor, certainly !!!
1x 1µs = 1µs ... 256x 1µs = 256µs ...
so, the maximum period is 256 µs ...
what was requested for, is a period duration of 10 ms ... or a 10,000 timer count !
Tell me if I'm wrong !!!
Alain
************************************************** ***********************
Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
************************************************** ***********************
IF there is the word "Problem" in your question ...
certainly the answer is " RTFM " or " RTFDataSheet " !!!
*****************************************
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Depends on what side you are standing at.
The "maximum" means fastest then.
Also, what do we get from TMR0 at 4Mhz at 1:4 prescaler ?
I get roughly 1.03ms.
I may be doing a wrong math here.
Last edited by sayzer; - 8th February 2008 at 19:11.
"If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte
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Use an LED for initial testing, make blinky first, otherwise, I'll bet you'll drive yourself crazy trying to get it to work right.
One 'easy-ish' way to get it to work...
Set up timer 0 to interrupt on overflow, get an 'On Interrupt' stub to work blinking an LED. Change the Tmr0 prescaler to 1:64. You'll get an interrupt every 16.384ms instead of 10ms. Yes, it's a bit longer than what you want, but you can easily scale the results from the 16.384ms interrupt to make them look like the results from a 10ms interrupt.
16384/10000 = 1.6384.
No, PBP can't divide by a fractional number...but, you multiply it up by a large number and divide it back down by a whole number, keeping the ratio the same to keep the numbers correct...i.e.
16384/10000 = 1.6384 which is the same as
32768/20000 = 1.6384 which is the same as...and so on and so on...
Or, set up Tmr1 as a 16 bit timer that kicks off every 10ms...just like the other guys said...
But $20 says you're biggest problem will be understanding how to get the interrupt to work in the first place...
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