gnupic: Re: [gnupic] Problems with USB PIC 18f2455
Subject:
RE: [gnupic] Problems with USB PIC 18f2455
From:
"Bradley Minch" ####@####.####
Date:
8 Mar 2006 00:28:51 +0000
Message-Id: <280CB384F3297641AB0C74674FB22A7D0646542B@OLINEXVS01.olin.edu>
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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