A 16MHz waveform repeats every 62.5nsec. If there is a 50ppm tolerance on the frequency, there will be a 50ppm tolerance on the period, which is 3.125psec.
This sort of question should be posted on sci.electronics.basics, or - better - dealt with by your instructor, who is paid to sort out this sort of elementary problem.
A 16MHz waveform repeats every 62.5nsec. If there is a 50ppm tolerance on the frequency, there will be a 50ppm tolerance on the period, which is 3.125psec.
or should i say that, there an timing tolerance of 3.125psec on the waveforms that i measured?
If you have a recent vintage digital scope, it may be able to make quasi-accurate measurements for you, but an analog scope most likely cannot get you much past 0.5%, you'll be measuring the scope not the component. Go grab a frequency counter.
I am measuring the "waveform" from GoLogic. The waveform doesn't not tally with the values being flash into the device that is used to produced the waveforms. It devaites by a few microsecs.
I was given that the device resonator's initial tolerance is 0.5%.
But 0.5% of what? Of one message frame? Of one OnTime? OffTime? Or OnOffTime?
So, how do I make use of the 0.5% tolerance to calculate the range of timing (in terms of +/- XXX microsecs)
All of the above, modulo jitter in the oscillator etc. It's all proportional, so percentages stay the same.
Suppose the time would be YYY microseconds (say the division ratio isn't exact so perhaps not exactly equal to what it would ideally be), the range of timing is YYY*0.995 to YYY*1.005, ignoring any jitter. The range in error is the difference between the ideal value and the above range of values.
With asynch serial RS-232 type communications the error in the bit position of the last bit is what you normally need to worry about (because it's the worst case situation), and it's about 10 times the error in the timing. So with a 0.5% resonator and perfect division ratio you'd have about a 5% error in the middle of the last bit time when the sampling takes place (assuming no jitter, perfect edges, and no error at all in the other side).
Best regards, Spehro Pefhany
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Thanks for the explination. I'm using the USB version of GoLogic.
btw, you mentioned that the timing would be YYY +/- 0.5%. So if my OnTime is 100us, so it should range from 95us to 105us. But I always thought the 0.5% should be for the whole frame or the whole message transmitted.
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