PIC32MX250F128B 32.768Khz Clock Unstable

Thread Starter

dcbingaman

Joined Jun 30, 2021
455
I am having issues with the following clock source:

PIC32MXCircuit.PNG
Sometimes the clock works other times it does not. If I hang two times 10 scope probes off pin 11 and pin 12 then the clock appears to work fine most of the time. Impedance of the scope helps make it work. I am really sick of dealing with such a precarious clock using the crystal. I have tried it with the 'recommended' 10Meg Resistor. That resistor caused it not to work at all. I have not tried the possible 330K resistor. Attached is the datasheet for the crystal. In either case, at this point, I think I can get a canned oscillator (Like the 8Mhz one shown) at 32.768Khz. These components are on a solderless breadboard for prototyping. I have found plenty of 32.768Khz canned oscillators but none that are simple through hole part like the 8Mhz oscillator. Any recommendations? Does anyone have a part number for a through hole 32.768Khz oscillator? I have kept the crystal as close as possible to the chip with the leads as short as possible. I have kept the two capacitors again as short as possible and as close to the chip as possible.
 

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MrChips

Joined Oct 2, 2009
24,432
Don’t hang any probes off pin-11 or pin-12. That will disrupt the crystal.
Follow the manufacturer’s recommendations for loading capacitors and resistor.

You have to find another way to monitor the oscillator frequency.
 

Thread Starter

dcbingaman

Joined Jun 30, 2021
455
True. I modified it the per exactly what the manufacturer recommended 10Meg parallel resistor and 470K series resistor. I did not have any 330K resistors handy but that fixed the issue. On my next digikey order I will get some 330K resistors. It appears to be working now, thanks for the input.
 
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