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PIC18F2550 doesn't start

 
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Jody



Joined: 08 Sep 2006
Posts: 182

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PIC18F2550 doesn't start
PostPosted: Mon Jul 02, 2007 7:06 am     Reply with quote
Hello,

I have build an example I found on this forum with the PIC18F2550 and USB..
http://www.ccsinfo.com/forum/viewtopic.php?t=24207&highlight=usb

I want to do it correct so I have made a PCB off it... I programmed it with the code like the example.... But most of the times the device doesn't apear in the Device Manager.... It is not regonised or cannot start...
And one out of ten it works fine......

What is wrong here????

Mine schematic and code:

http://home.casema.nl/elselinde.wisman/

Thanks in advance,

Jody
Ttelmah
Guest
PostPosted: Mon Jul 02, 2007 7:50 am     Reply with quote
Where is your decoupling?.
You show Vusb, being decoupled to Vcc (normally you would decouple to GND), bt then show no decoupling between Vcc, and GND at all....

Best Wishes
Jody



Joined: 08 Sep 2006
Posts: 182

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PostPosted: Mon Jul 02, 2007 8:15 am     Reply with quote
Fixed that...stupid mistake...
but the behavior is the same.... :-(
Ttelmah
Guest
PostPosted: Mon Jul 02, 2007 8:28 am     Reply with quote
Try increasing the capacitor used on Vusb.
There is a known 'oddity' with these chips behaving funnily, which requires a larger capacitor on here to fix. Might be the problem.

Best Wishes
Jody



Joined: 08 Sep 2006
Posts: 182

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PostPosted: Mon Jul 02, 2007 9:13 am     Reply with quote
Oke I will try that,

Thanks I will keep you informed....

Jody
Jody



Joined: 08 Sep 2006
Posts: 182

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PostPosted: Tue Jul 03, 2007 1:22 am     Reply with quote
Fixed it !!!!!!!!!!
Thanks....
It was the decoupling.... there was a lot of noise on the USB power...

Jody
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