pic18f887 event timer

[cpayne]

I am using a PIC18F887 with the internal oscilator set @ 8MHz. I have a subroutine I need to fire off at a routine basis (nominally every 22ms although I want it a constant that I can tune). Can someone give me a crash course (with as much details so I don't have to ask a bunch of follow on dummy questions) on how I set this up as some sort of timer on an interupt, preferably without using assembly, but if that is the only way, I am willing to try. I have no available IO pins remaining if that matters. I am using no other interupts, but future versions may entail a serial interupt. I only want it to fire after a complete line is executed, which I think is by default, then return to the next line after it runs the routine. I suspect its fairly easy, but I am not sure where to start.

Thanks,
Charlie

[mackrackit]

http://www.picbasic.co.uk/forum/showthread.php?t=3251
Be sure to read the first eight post.

[cpayne]

OK. This looks good. Thanks.

I think the overkill blinking light is the right for me to use. I am unlear what to change to get timer 1 to fire off every 22ms.

I assume it starts with this seting
T1CON = $31 ; Prescaler = 8, TMR1ON

I have two different harware setups I am trying to put it in. Both use the PIC16F887, one with an external 20MHz Osc, the other with an internal 8MHz. It looks like a prescaler of 1:8 is the max, so I suspect I need to do a counter in the interupt routine that only fires my event every nth time to acheive the 22ms event? Is this a big burden or is there a simpler way? Can someone show me some examples of how to do the math to get the event to fire off properly with the two oscillator speeds?


Thanks,
Charlie

[aratti]

Can someone show me some examples of how to do the math to get the event to fire off properly with the two oscillator speeds?

Charlie, play with the attached little tool to find out.

How to use it: click on the box enter the new value and press enter.

Cheers

Al.

[mackrackit]

Timer 1 is 16 bit.
At 8 Mhz with a prescale of 1 and a peload of 21537 will give 22.0 mSec
At 20 Mhz with a prescale of 2 and a peload of 10536 will give 22.0 mSec

http://www.picbasic.co.uk/forum/cont....-PICMultiCalc
http://www.picbasic.co.uk/forum/show...3259#post23259

[cpayne]

I am not sure if I shoudl reply to this thread or the main interupt thread.

Anyways, I am getting errors when compiling. It looks like its all with the includes files.

I have attached a screenshot showing the errors and my code

Can anyone let me know what I am doing wrong?

Thanks,
Charlie