8 bit timer was more accurate for me likely due to my implementation. I used timer interrupts for the count (to step a variable). A 8 bit timer interrupts more often, at a count of 0xFF instead of 0xFFFF.
Sent from my iPhone > On Jul 8, 2016, at 1:13 AM, 'Oliver Seitz' via jallib > <[email protected]> wrote: > > > Matt wrote: > > Using a prescaler reduces accuracy > but would let you count at a higher frequency. Using a 8bit > timer instead of a 16 bit timer is more accurate. > > Hi Matt! > > The plan is to use a 12f1572. According to the datasheet, both TMR1 can count > up to 16,666MHz without or 33,333MHz with internal prescaler. To count the > max. prescaled frequency, core clock must be 32MHz with prescaler=8. > > TMR0 can handle shorter pulses, but the period is like for TMR1 defined as > "Greater of: 20 or (Tcy + 40)/prescale value". Min Tcy is 200ns, so the > second term can never go below (240/8=) 30. This may be a datasheet error, > but the way it is written it won't count faster than 33,333MHz. > > If you're counting, say, 10000000Hz or 10MHz, a prescaler value of 8 > introduces a possible error of -7Hz, because there may be counts left in the > prescaler which cannot be read. The internal oscillator is to be used as > reference with +/-2% of accuracy, or +/-200000Hz. Even when using a crystal > with +/-15ppm, the reference introduces a possible error of +/-150Hz. > Therefore, when it comes to higher frequency, I'd say the prescaler error can > be accepted. When the frequency appears to be low, the prescaler can be > switched off. > > I can't imagine however why using an 8-bit counter should be more accurate. > > Greets, > Kiste > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/jallib. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "jallib" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/jallib. For more options, visit https://groups.google.com/d/optout.
