piclist 2001\10\18\062552a >
Thread: Extending TMR2
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face BY : Mike Blakey email (remove spam text)



Thanks for the reply, This is exactly what I was looking for, the only problem I
have is that during the pulse period the PIC is 'busy' doing some other stuff!  I
think I'm going to have to do as you have suggested, even counting several
interrupts will give higher resolution, but may cause me stack problems, which is
what I am trying to avoid.

Thanks for the help.





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Subject:        Re: [PIC]: Extending TMR2

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>I'm currently using a 16f876 20Mhz. in an application.  I need to delay an
>output
>between 0.06s and 0.003s.
>
>I have pre and post scaled to 16 on TMR2 but can only get a max. delay of
>0.029s  I
>can not afford the overhead of waiting and counting interrupts. does anyone
>have
>any *smart* ideas to extend the time period?

Maybe this isn't what you're looking for, since you haven't included any
details about the function of your program, but, how about this:

1) Clear a flag bit when you set your output low (for example)
2) When you get your .029s interrupt, check the flag bit.  If clear, set it.
 If set, then change your output high (2*.029s ~ .06s).

Of course, you'd have to set your delay for 1/2 of what you need, then use
the flag to double it.

I'm not sure if you need better precision, but since you mentioned a range
of .003s and .06s, this might be good enough.  And you'd only have a .002s
max error (assuming your max. delay possible is REALLY .0290 seconds) with
the flag's doubling effect.

--Andrew

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