Well, then it will make it simpler to use low frequency OSC, such as
standard 32768HZ, using timer0 will give you a tick every 32ms. This
is a 32 bit variable in a year, directly supported by many C
compilers.

Either way, incrementing  a variable on every interrupt call with the
max timer setting you can afford, will require to handle a multi-byte
variable in RAM that is not difficult to maintain even in ASM. Using
the carry bit you can handle extremely large multi-byte variables with
easy.

2008/4/14, Dave Roseman <dave@transpower.uk.com>:
> This is a long term timing application, the resolution is 60 minutes, and
> would expect it to be in service for years, possibly having a count every
> 200us might lead to a too large number..
>
> --dave
>
> -----Original Message-----
> From: Ariel Rocholl [mailto:foros@arocholl.com]
> Sent: 11 April 2008 16:03
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] Measuring time a DC signal is on
>
> Depending on how long that measure can be (seconds? days? years?), you
> will need:
>
> * A timer (better 16bit one than 8bit one, you can choose depending on
> it not being already allocated for a peripheral). Take a look on the
> datasheet, it is straightforward to enable a timer.
> * A timer interrupt, to increment a global variable that will count
> how many times the timer carried over.
> * A global variable. Let's say that depending on your timer, OSC
> frequency and pre/postcaler, you have an interrupt every 200uS. The
> variable will increment once every 200uS so depending on how many of
> these ticks you need to count, this may go to a 32bits or even 64bits
> variable.
>
> 2008/4/11, Dave Roseman <dave@transpower.uk.com>:
> > Hi,
> >
> >
> >
> > I am using a PIC16F690 to monitor how long a power supply is active for,
> but
> > I have no idea how to use the timer in the micro to monitor this signal.
> It
> > does go high when the power is on, but how to get this info to the micro,
> I
> > don't know.
> >
> >
> >
> > Also, this reading is required to be cumulative, so has to remember the
> > previous on time and append to it.
> >
> >
> >
> > I'm just starting PIC programming, so please forgive me if this is too
> > simple or obvious a question.
> >
> >
> >
> > Regards
> >
> > Dave Roseman
> >
> > --
> > http://www.piclist.com PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
>
>
> --
> Ariel Rocholl
> Madrid, Spain
>
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>


-- 
Ariel Rocholl
Madrid, Spain
-- 
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