gnupic: Re: [gnupic] Problems with USB PIC 18f2455
Subject:
Re: [gnupic] Problems with USB PIC 18f2455
From:
Nicholas Robinson ####@####.####
Date:
18 Mar 2006 06:12:42 +0000
Message-Id: <200603180611.33223.npr@bottlehall.co.uk>
Hi Brad and Wojciech
I'm very sorry for the long overdue reply of thanks for your emails and useful
advice. It's that time of term for schoolteachers and I have been writing
reports instead of doing more interesting things!
I will implement the changes you suggest.
Thanks
Nick
On Wednesday 08 March 2006 00:28, Bradley Minch wrote:
> Hi Nick,
>
> Are you using the port of the lab2 firmware or have you modified it? If
> you have modified it, have you actually tried to get the original to work
> in your hardware? Two things about Alan's hardware that you may need to
> change besides replacing the 6-MHz crystal with a 4-MHz one is to eliminate
> the external 1.5 kOhm pull-up resistor between VUSB and D-. The 18F2455
> has internal pull-up resistors and, unless you have changed the InitUSB
> subroutine to not make use of the internal pull-ups, you shouldn't have the
> external one. Second, you should have a bypass capacitor between the +5V
> VBUS and ground. I typically use a 10-uF tantalum cap in parallel with a
> 0.1-uF ceramic cap. The USB specification recommends a bypass cap of
> between 1 uF and 10 uF. The 0.3-uF cap between VUSB and ground shown in
> Alan's schematic should probably also be a ceramic cap, too.
>
> Brad Minch.
>
> -----Original Message-----
> From: Nicholas Robinson ####@####.####
> Sent: Tue 3/7/2006 6:25 PM
> To: ####@####.####
> Subject: [gnupic] Problems with USB PIC 18f2455
>
> Hi
>
> A few weeks ago, I emailed about problems getting a PIC 18f2455 to connect
> via USB. I was advised to post to the usb mailing list but this proved no
> help. I wonder if anyone can help? I would like to avoid spending £120 on a
> debugger if I can as it is a hobby project and probably doesn't justify the
> spend.
>
> I've used Alan Macek's circuit as the basis for mine and with 4 MHz chip.
>
> I've used Ben Dugan's macros for gpasm and Brad Minch's lab2 application.
>
> Using dmesg I get:
>
> usb 2-2: new low speed USB device using uhci_hcd and address 3
> usb 2-2: device descriptor read/64, error -71
> usb 2-2: device descriptor read/64, error -71
> usb 2-2: new low speed USB device using uhci_hcd and address 4
> usb 2-2: new low speed USB device using uhci_hcd and address 5
> usb 2-2: device descriptor read/64, error -71
> usb 2-2: device descriptor read/64, error -71
> usb 2-2: new low speed USB device using uhci_hcd and address 6
> usb 2-2: device descriptor read/64, error -71
> usb 2-2: device descriptor read/64, error -71
> usb 2-2: new low speed USB device using uhci_hcd and address 7
> usb 2-2: device not accepting address 7, error -71
> usb 2-2: new low speed USB device using uhci_hcd and address 8
> usb 2-2: device not accepting address 8, error -71
>
> When I plug the circuit in. Usbmon doesn't really show anything more
> exciting.
>
> I've put some 'debug' into the application so that it blinks leds at
> various times and these light up after a few seconds (not sure if this
> delay should be expected, my last experience of interrupts and such low
> level programming was on a z80). One odd thing is that after trying out the
> circuit, the mouse (the only other device on the same usb hub) stops
> working and has to be unplugged and replugged many times to get it working
> again (or the machine rebooted if I get bored first).
>
> My theory, such as it was, was that I had made a mistake working out the
> frequency config fuse settings and so the usb wasn't being driven at the
> correct frequency. However, I've now tried every combination as far as I
> can tell and nothing works. The usb hub is quite old and only low speed,
> but I've tried it on other machines (even windows) and it doesn't come up
> with anything like a valid device.
>
> I'm running fedora core 4 with kernel 2.6.15-1.1831_FC4.
>
> Thanks for any help you can give.
>
> Nick
>
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