Like most things on a computer the timer runs off a quartz crystal
oscillator. The fundamental frequency of a crystal is determined by its
length. Therefore, manufacturing tolerances with respect to the length
determine how close the crystal's actual frequency is to the desired
frequency. Because of manufacturing tolerances no two crystals will
have the exact same frequency. This means that the amount of drift is
unique between any two crystals. If you want to synchronize two
different timers the thing to do is to assume that one of the timers is
your master timer and use it to compare and correct the time on the
other timer. One way is to use a two channel oscilloscope to determine
the difference in frequency. If you have a 10 MHz frequency and a 1 MHz
difference, then every second you lose 1/10th (1 MHz/10 MHz = 1/10th) of
a second. And your error is - 1/10 Sec per Sec. The rate is a constant
either negative or positive. It does not change unless the two crystals
are subject to different temperatures. Now, figure out how much time
it would take for this clock drift to equal one increment of the
timer. Then correct your timer by adding or subtracting one when ever
this amount of time passes.
But, more importantly, what is your application? Your application maybe
able to get by with just resetting both timers at the same time through
a port.
Hideo Sato wrote:
>
> Hi! Thanks for your help.
>
> On Tue, 18 Jan 2000 09:52:39 +0000
> Paolo Mantegazza <[EMAIL PROTECTED]> wrote:
>
> > > By the way,
> > > "RT-Linx" uses "8254-timer-chip" to manage real-time tasks.
> > > I want to know the accuracy of "8254-timer-chip".
> > > Where can I get the infomation?
> > it runs at 1193180 Hz.
>
> Yes, I know it.
> But, I think "8254-timer-chip" has an error range.
>
> For example,
> "the errors of plus or minus 1 micro second per 1 minute"
>
> I want to have the exactly same period between 2 computers.
>
> Regards
>
> /-------------------------------------------/
> Department of System Design Engineering
> Keio University Yako Laboratory
> Hideo Sato
> E-mail [EMAIL PROTECTED] (Univ. )
> /-------------------------------------------/
>
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