> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of peter green
> Sent: Tuesday, November 07, 2006 1:21 PM
> To: Microcontroller discussion list - Public.
> Subject: RE: [PIC] USB device detected at wrong speed
> 
> 
> > Hi Peter, VUSB and VBUS are just too similar to each other! 
>  Yes, that 
> > is one of the first problems I found and it did blow up the 
> USB section
> > of the first chip.   I see that I failed to note that change in the
> > "changes for rev 1.1" notes on the schematic but rest assured it's 
> > been fixed on the board itself.  I replaced the PIC with a 
> new one and 
> > that got me from nothing at all, to the current state of 
> partial enumeration.

> ok, another thing to check, by default the microchip code is 
> set up for bus sense IO, you do not seem to have such a 
> circuit on your board, reading a floating input could well be 
> the cause of strange results.

Is that the circuit and code that checks to see if the circuit is self
or USB powered?  I left the circuit out because this project will always
be self powered, and I think I "tied off" the code to always indicate
self powered.  I'll check.

> 
> also i have discovered that putting a drain resistor on the 
> main power rails considerablly improves reliability of startup.

This improves regulator stability or uC reset/startup?

> 
> also the caps are physically close to the chip right?

Yes.

> 
> finally i see while you've put in the low value, low esr 
> close to the chip part of decoupling you don't have any large 
> cap on the power rails, a quick search for the regulator you 
> are using says that it should have a 22uf cap on its output.

I've fixed that also.  From the list of changes section, here is what
has been corrected so far on the board:

VBUS and VUSB no longer connected.
VBUS has 100K pulldown
VUSB has .47uF cap
capacitor added to regulator, across Vout and GND

thanks,
--steve


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