ft232r USB chip - need debug help

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Zalfrin
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Posted by Zalfrin: Thu. Jun 8, 2006 - 06:35 PM
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Recently, our client has asked us to add USB support to an already existing design based on the Mega32 microprocessor. We decided upon the FTDI FT232R chip to drive this communication. The schematic for this chip is taken directly from the 232R datasheet for "self-powered configuration". Unfortunately, I have been unable to communicate with the chip. When I power on the unit, windows detects a usb device, but is unable to figure out what it is. Using USBView, I found that no information is being returned by the FTDI chip, and connection status is listed as "DeviceFailedEnumeration".

I've probed all the incoming voltage levels. VCCIO and VCC are tied to 5V, Reset# is sitting at 3.5V, the 3.3V output is at 3.3V, and grounds are at ground. I am also able to see some communication on the USBDM and USBDP lines, although my scope isn't fast enough to really see the signals. Does anyone have any experience with debugging this chip? I notice that the old BM model allowed you to check if the oscillator was operating properly, but I can't find that mentioned for the R model. At this point, the only thing I can think of is that the chip could be bad.

I've attached the schematic for this chip, I'd appreciate any thoughts you guys might have.

Thanks.

Attachment(s): 

Image icon usb.JPG

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AVR Microcontrollers, megaAVR and tinyAVR
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Guillem Planisi
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Posted by Guillem Planisi: Thu. Jun 8, 2006 - 06:42 PM
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This week I finished to mount a test board with 232BM, and it worked at first glance. Since I don't know the version you have, perhaps I'm wrong, but for 232BM, there should be an external resistor 1.5K between 3V3 and USBDP in order to inform the bus that there is something pluged.

I had also some similar problem when I mounted an eeprom that was not new, then I should program it with MProg. Then it worked fine.

Of course, all lines should be examined, and a hard problem can't be discarded.

Have luck,

Guillem.

Guillem.
"Common sense is the least common of the senses" Anonymous.

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Zalfrin
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Posted by Zalfrin: Thu. Jun 8, 2006 - 06:49 PM
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Supposedly the R model removes the need for all the external components that you needed for the BM, so I don't think thats the issue. The R model has all that pull-up stuff taken care of, as well as the eeprom and oscillator. Theoretically, it should be really easy and nice to work with. Unfortunately, that hasn't been the case for this particular board, and the documentation for debugging the chips on FTDI's website is specific to the BM model, and I'm not sure how much of it actually applies to this chip. For example, the debug app note for the BM says that you can ground the reset pin in order to see if the oscillator is functioning. That does not seem to be the case for this chip, but I could be wrong.

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CountZero
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Posted by CountZero: Thu. Jun 8, 2006 - 06:57 PM
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Don't know if this is any help but...

I had some trouble connecting a mass storage device, windows kept saying "unknown device". I removed all USB related things and after that just "scan for new devices" and everything worked.

Edit: by everything I mean everything; host controllers, hubs and anything else...

Last Edited: Thu. Jun 8, 2006 - 07:01 PM
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John_A_Brown
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Posted by John_A_Brown: Thu. Jun 8, 2006 - 06:57 PM
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We have reset unconnected, and 3v3 out unconnected. VCCIO goes to AVR Vdd (3.3V). Works fine.

Four legs good, two legs bad, three legs stable.

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Zalfrin
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Posted by Zalfrin: Thu. Jun 8, 2006 - 08:03 PM
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I'm going to try pulling the reset line so it floats, if it doesn't work after that we'll try replacing the chip. I very much doubt that the floating reset will improve things since that connection is designed to prevent sending data to a powered down USB port and I know power is coming in from the port, but its worth a shot.

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CountZero
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Posted by CountZero: Thu. Jun 8, 2006 - 08:28 PM
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Consider testing it on another computer, or perhaps under linx.

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MegaUSBFreak
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Posted by MegaUSBFreak: Thu. Jun 8, 2006 - 10:07 PM
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Hi,

the 232R is a small package where accidentely two pins can be shorted. Please check this.

Also check if the the wiring of the usb cable is correct.

Did you install all the necessary drivers (one for the USB and one for the VCP, once started it should do it automatically)

FTDI sells complete cables for your application. USB on the one side, UART (TTL/CMOS) at the other side.

I used FTDI chips many times, usually without any problems..

Klaus
********************************
Look at: www.megausb.de (German)
********************************

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Bronze Markjs
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Posted by js: Thu. Jun 8, 2006 - 10:27 PM
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Quote:
Did you install all the necessary drivers

This is important!! FTDI tells you to unplug your internet connection when installing the drivers or Windows will try and install it's own and will not work. I'm interested in this because I'm in a similar situation :-) I have the 232R chips but haven't got anywhere to solder them onto yet but I'm getting a preassembled board from Futurlec to play with until the (prospective) client decides if they want to go ahead OR I'm doing some other proto boards where I can add a few prototypes.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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arteitle
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Posted by arteitle: Fri. Jun 9, 2006 - 02:35 AM
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Two things that were helpful in solving enumeration problems for a project I've worked on were to add 47pF caps between each of the USB data lines and ground, and a 0.1uF cap between USB shield and ground. This was with the FT232BM, which is essentially the same chip but without the integrated EEPROM and oscillator. These suggestions came from some of the FTDI knowledge base articles.

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Zalfrin
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Posted by Zalfrin: Fri. Jun 9, 2006 - 03:17 PM
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Thanks for the suggestions, guys. I found the problem finally. I had hooked up a surfboard in isolation and got the chip to talk. When I checked the PCB layout, I found that the two differential lines had been swapped. That'll teach us to trust Orcad's footprints. ;-)

MegaUSBFreak: Unfortunately, windows wouldn't let me install any kind of drivers for the device because it couldn't figure out what it was. I could try to manually update the drivers for the unknown usb device, but windows would complain that the directory I specified did not contain information about the device.

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John_A_Brown
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Posted by John_A_Brown: Fri. Jun 9, 2006 - 05:09 PM
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js wrote:
Quote:
Did you install all the necessary drivers

This is important!! FTDI tells you to unplug your internet connection when installing the drivers or Windows will try and install it's own and will not work. I'm interested in this because I'm in a similar situation :-) I have the 232R chips but haven't got anywhere to solder them onto yet but I'm getting a preassembled board from Futurlec to play with until the (prospective) client decides if they want to go ahead OR I'm doing some other proto boards where I can add a few prototypes.

Windows (XP at any rate) drivers work just fine, provided you want to use Virtual Com Port drivers. It's only if you need the D2xx drivers that you need to unplug the illiternet, and then only if you have ticked the box which allows XP to automatically search the web for drivers without prompting.

Four legs good, two legs bad, three legs stable.

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