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Student Learning. Student Health and Wellness. Workforce Development. Teaching Profession. Keep in mind that humidity can have a huge affect on low power oscillation amplifier operation. Thank you Fausto bartra. We would have to see your code and PCB layout to make any useful comments. We have built about 20 of these boards About five of them the clock does not work at all The ones that work I am using 22pf cap??
I also tried 22pf on these five boards but they dont work The code is correct other wise it will not work at all The layout is two 0. How do you calculate the load capacitor? Hi, According to circuit schematics for board with PIC32MXFL, that I have running: mikromedia plus development board from mikro elektronica, there are 22pF capacitors used both for secondary crystal oscillator, and for the primary crystal oscillator, and they both work as expected.. Value of the capacitors should be according to what was used when crystal was trimmed during production.
But load capacitance CL given in datasheet for crystal resonators, is the resulting capacitance as seen from the crystal, so when there are 2 capacitors in a Pierce oscillator circuit, they act as if connected in series.
There are general formulas for calculating resulting capacitance of combinations of components. Generally, variation in capacitor values, should not prevent the oscillator from operating, it is sometimes used to tune the frequency in precision temperature controlled crystal oscillators.
Watch crystals are designed to work at low power levels, and microcontroller designers compete in making crystal oscillator amplifiers that work with low power consumption. This have been taken so far that the secondary crystal oscillator in PIC32MZ devices do not work at all. As mentioned in messages above, circuit digram of oscillator internals is not published, and amplifier characteristics is obscure.
There is some kind of automatic gain control AGC and secondary crystal is expected to work with less than 1 V voltage sving peak to peak. Doing measurements on crystal oscillator is difficult. Probe capacitance is likely to change circuit conditions, such that circuit that do not work, may start working when touched by oscilloscope probe.
Or opposite. And it will pull the frequency of oscillation, but that may not matter for short measurements. I have used a X oscilloscope probe with some success. It is a probe for mains voltage measurements, but also have good performance for a passive probe. There are active probes that may be used.
For serious analysis, active current-sensing probe have been recommended. Mysil: thank you for your reply I just noticed your comment: "This have been taken so far that the secondary crystal oscillator in PIC32MZ devices do not work at all.
Thanks Fausto Bartra. Please show us the layout and the schematic for at least the oscillator section. For revision B2 production, the secondary oscillator should be able to work. JP We removed and re-insalled new capacitors and now it seems to work??!!!
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