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FT232RL woes... — Parallax Forums

FT232RL woes...

FlyingFishFingerFlyingFishFinger Posts: 461
edited 2010-04-13 20:20 in General Discussion
Hi all-
You might remember my question from last week about the malfunctioning AVR. Well we solved that problem (turns out that it was a missing setting in the software, but the FTDI on that board is blown anyway), but I built a new one this week anyway.
The new problem? The FT232RL appears to constantly reset itself when you plug it in. Any computer detects it as a USB-Serial converter, but it starts resetting itself when a COM port is assigned.
I've gone over the datasheet, my design and the Arduino we based it on many times and can't seem to come to a consensus.
I have the TEST pin grounded and the RESET line pulled high as the datasheet states. The Arduino Nano schematic doesn't do this, but it seems another developer has ID'd this as a mistake:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1263958401
I already had his solution implemented, and also tried not powering the board off USB. In all cases, no go. Consistent resetting every half a second or so. Windows 7 Device manager tells me: "This device cannot start. (Code 10)"
Any ideas? My apologies if I'm missing something obvious...this board is really starting to stretch my patience and nerves [noparse]:([/noparse]

Rafael

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UC Berkeley '12 EECS
CalSol: UC Berkeley Solar Car
http://calsol.berkeley.edu
KJ6AWU

Comments

  • LeonLeon Posts: 7,620
    edited 2010-04-12 10:23
    Schematic?

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    Leon Heller
    Amateur radio callsign: G1HSM
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2010-04-12 20:41
    Well, you said the TEST pin is grounded. That pin floating can certainly cause that issue. There is no need to pull the RESET# line high, but you can. Are you drawing any power from the 3.3V regulator on the FTDI chip? It shouldn't be used as any more than a reference for VCCIO.

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    Chris Savage

    Parallax Engineering
    ·
  • FlyingFishFingerFlyingFishFinger Posts: 461
    edited 2010-04-12 20:56
    I have the 3V3Out tied to my 3.3V bus. Here's a schematic of the board, the FT232RL is on the left.
    Thanks!

    Rafael

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    UC Berkeley '12 EECS
    CalSol: UC Berkeley Solar Car
    http://calsol.berkeley.edu
    KJ6AWU
    pdf
    pdf
    Schematic_v1.5.pdf
    69K
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2010-04-12 22:02
    That may be part of your problem. The schematic is a little hard to follow...it looks like you've designated connectors as ICs for example. In any event, it's as if you're simply tying all your power points together that are at the same voltage. The 3.3V out from the FTDI chip is now connected to the 3.3V output of your LM3940. I wonder if the internal regulator in the FTDI chip is cycling?

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    Chris Savage

    Parallax Engineering
    ·
  • FlyingFishFingerFlyingFishFinger Posts: 461
    edited 2010-04-12 22:34
    Yeah about the labelling...that's the default DipTrace put in I think. The labelling for the connectors doesn't show up on the silkscreen but that does explain the discontinuous numbering on the actual IC's.
    Anyway, what's the problem with tying all my 3.3V together? That's the way the Arduino's appear to do it and they work as far as I can tell...,unless I'm somehow drawing current from it. I shouldn't be doing that because everything on the board runs at 5V; the 3.3V is for external devices if they need it.
    Thanks

    Rafael

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    UC Berkeley '12 EECS
    CalSol: UC Berkeley Solar Car
    http://calsol.berkeley.edu
    KJ6AWU
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2010-04-12 22:59
    Usually a circuit has one voltage supply rail for a given voltage and all the other tags are points that obtain voltage from the source. You're typing multiple outputs together. It's basically the same as putting regulators in parallel and not a good idea, especially when they're different types. I also don't think you should have the USB voltage connected to the 5V supply. Yes you have the diode there, but the USB port can only supply ~100mA unless the FTDI chip is programmed to request ~500mA.

    You should either be powering the FTDI chip from USB, or from your circuit, and you should only be connected to the 5V rail, not the 3.3V rail.

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    Chris Savage

    Parallax Engineering
    ·
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-04-12 23:56
    If, as your schematic indicates, the FT232R's RESET# pin is connected to the cap output from DTR, that is probably your problem. Just cut the trace to RESET#, and your problem should go away. The way it's wired, every time you connect something, DTR will change state causing the FT232R to reset, which probably entails another enumeration, leading to an endless loop of resets. As Chris pointed out, you simply don't have to connect RESET# to anything -- but especially not to DTR.

    -Phil
  • FlyingFishFingerFlyingFishFinger Posts: 461
    edited 2010-04-13 02:17
    Ah, okay, that makes of sense.
    @ Phil-
    The Arduino Nano is actually wired with the cap from DTR line (so the software can do a reset), but they don't connect the reset line.
    So I gather that corrections I should make are a) disconnect the 3V3 line from the main regulator and b) disconnect the FTDI's reset line from the main reset line.
    @ Chris-
    The diode is there so that I can choose what I want to power the board from, USB or an external source. That should work. right?
    Thanks guys!


    Rafael

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    UC Berkeley '12 EECS
    CalSol: UC Berkeley Solar Car
    http://calsol.berkeley.edu
    KJ6AWU
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2010-04-13 20:20
    @Phil - Nice catch, I didn't notice the DTR line tagged to the reset port.

    @FFF - The only thing I was getting at about the power supply coming off the USB is that, unless the FTDI chip is programmed to request high current mode, your total current draw can not exceed 100mA when powering from the USB.

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    Chris Savage

    Parallax Engineering
    ·
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