[PIC] Weird problem with PIC32MX795F512L

[kunaltg]

Hey I am using PIC32MX795F512L for my project but experiencing a weird problem !

After soldering this IC on my board , MPLAB can detect controller & I can program this controller using MPLAB successfully. But the board is not working properly (Note:- The program downloaded in the controller is 100% working )

while troubleshooting, I noticed that, I am getting 192Khz clock across 32Khz crystal ! I tried this with multiple boards & controllers , But same; 192Khz across 32Khz crystal.

But this whole system is working on one board without issues :!: ! Please help me !! how can i get 192Khz across 32khz ??? :!: :-(

 

[zeyad.kassaby]

Re: Weird problem with PIC32MX795F512L !! Please Help !!

hi kunaltg
I am trying to help you ,there is some info i need to know
1) do you see this 192 khz on vcc also
2) what do you mean with the whole system is working on one board without issues

with best regards
Ziad

 

[nick703]

Re: Weird problem with PIC32MX795F512L !! Please Help !!

post circuit diagram...

But this whole system is working on one board without issues

because your code is working on another board then of course problem in your created hardware bro!!!!

 

[xpress_embedo]

Re: Weird problem with PIC32MX795F512L !! Please Help !!

I too had the exact problem, as per some schematics used in microchip hardware i found that they had used 11pf capacitor for RTCC Crystal, and even i had also used that.

When changing these capacitors to 22pf my setup works fine, so tell me what value of capacitors you are using with RTCC crystal.
Even in my case i get 195KHz wave with 11pf and it gets corrected after using 22pf Capacitor.

 

[Dan Mills]

Re: Weird problem with PIC32MX795F512L !! Please Help !!

32K tuning fork crystals are generally fairly critical with respect to load cap and you need to ensure that you pick a part matching the specified requirements of the oscilator in use or you will get funnies like this.

The things are a bit of a pain to deal with and if you can I would always much rather use something faster unless power is a real concern.

Regards, Dan.

 

[kunaltg]

Re: Weird problem with PIC32MX795F512L !! Please Help !!

@zeyad.kassaby

1) No Only across 32kHz crystal ! VCC is OK & even another 8Mhz clock is also OK !

2) I mean , i am having 3-4 PCBs of the same project, & 1 of them is working fine, others are not working !!

@nick703

as I told above the working board is also developed by me only !!

@xpress_embedo

Thank you bro, i am using 10pF caps instead of 11pF(i thought its not that critical) , But i think your solution will work for me too :razz: ,, I will try it soon !! currently I am out of station !

@ Dan Mills
I will check its compatibility !, but i think the resolution suggested by xpress_embedo will work for me too !!

 

[xpress_embedo]

Re: Weird problem with PIC32MX795F512L !! Please Help !!

@kunaltg

Yes it will work for you for sure.

I made a circuit as per the schematic diagram Of microchip pic32mx795f512l i think it was usb starter kit 2.
I am copying from that, then faced the similar problem, after changing the values from 11pf to 22pf everything works fine.

 

[kunaltg]

@xpress_embedo

Hey i tried ur solution !! no sucess (clock is 192kHZ ONLY)

But i came to know that my board's problem is not the RTCC !! My board works fine without RTCC crystal ,, the problem lies in 8Mhz crystal !! My board starts working if i short clock pins(on controller) for short time ,,this is also weird thing ,,But my board works perfectly if i replace 8Mhz crystal with 4Mhz !! Please help to resolve this issue !