[Gmecm] Any USB developers out there?

[Steve Ravet]

Craig, thanks for the suggestions.  I brought it in to work today and
found something interesting.  When the board is powered up, no USB cable
connected, the 20 MHz crystal oscillates fine.  When I plug in the USB
cable the OSC gets distorted, then goes flat after about 1 sec.  As soon
as I pull out the USB cable the OSC comes back.  This is some kind of
loading issue?  The PIC has some internal settings related to the OSC,
I'll have to double check them.

thanks,
--steve 

> -----Original Message-----
> From: gmecm-bounces at diy-efi.org 
> [mailto:gmecm-bounces at diy-efi.org] On Behalf Of Craig Moates
> Sent: Thursday, November 09, 2006 11:51 AM
> To: gmecm at diy-efi.org
> Subject: Re: [Gmecm] Any USB developers out there?
> 
> Steve,
> 
> Definitely check the crystal and capacitor areas. Those are 
> ceramics you are using for the 18pF set? Check that it's set 
> up for 18pf on the xtal desired capacitance?
> 
> I'd be possibly concerned with how the trace is run on that 
> 1M there by the xtal. Could be some induced stuff going on? 
> Also, doesn't the pic have the load built in?
> 
> Considered adding caps to gnd on the USB lines coming in? 
> Could be picking up some noise, I like to put like some 47pF on there.
> 
> I assume you've tried even after a hard reset via your switch 
> in there, right? Just wondering about brownout issues and 
> that sort of thing.
> 
> Have you tried it with just the USB, PIC, xtal, and 
> resonator/decoupling caps connected? Could help to step in 
> slowly to see what's 'not' causing the problem. I know I 
> always get excited, assemble the whole thing, and then step 
> back to find one trace or leg that isn't going where it should.
> 
> Best regards,
> Craig Moates
> 
> 
> 
> ----- Original Message -----
> From: "Steve Ravet" <Steve.Ravet at arm.com>
> To: <gmecm at diy-efi.org>
> Sent: Monday, November 06, 2006 10:02 PM
> Subject: RE: [Gmecm] Any USB developers out there?
> 
> 
> 
> > -----Original Message-----
> > From: gmecm-bounces at diy-efi.org
> > [mailto:gmecm-bounces at diy-efi.org] On Behalf Of Paul Smith
> > Sent: Monday, November 06, 2006 8:10 PM
> > To: gmecm at diy-efi.org
> > Subject: Re: [Gmecm] Any USB developers out there?
> >
> > I would'nt call myself a USB expert but would be willing to
> > help if you do not get any other volunteers.
> >
> > I have worked a bit with the 18f2550 series that supports USB.
> >
> > Paul
> >
> 
> 
> Hi Paul.  I have uploaded the project to the TWiki page:
> 
> http://www.diy-efi.org/twiki/bin/view.pl/Gmecm/UsbVpw
> 
> I think the problem is in hardware instead of software.  I am testing
> the board with a keyboard/mouse demo that is supposed to move 
> the mouse
> in a circle and send keystrokes.  This firmware works on the PIC demo
> board that I bought, but it doesn't work on my PCB.  I ran usbview.exe
> to see that most of the enumeration is correct except the 
> last 4 items:
> 
> my board                              demo board
> ----------------------------------------------------------------
> Current Config Value: 0x00            Current Config Value: 0x01
> Device Bus Speed: Low                 Device Bus Speed: Full
> Device Address: 0x00                  Device Address: 0x01
> Open Pipes: 0                         Open Pipes: 1
> 
> That stuff is clear as mud to me.  The thing that stands out 
> is the Bus
> Speed.  I don't know why my PCB shows up as Low while the 
> demo board is
> Full.  I have checked the D- and D+ lines and the pullup is 
> in the right
> place.
> 
> I am using the PIC18F2455.  I posted to the microchip forums also and
> got some suggestions but haven't found the answer yet.  That thread is
> here:
> 
> http://forum.microchip.com/tm.aspx?m=185797
> 
> thanks for any help,
> 
> --steve
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