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Problem with FT245BM

Discussion in 'Embedded' started by Bertolt Mildner, Jul 13, 2004.

  1. I have a strange problem with a FTDI FT245BM USB interface IC.

    As soon as i enable the "pull down IO pins in USB suspend" option in the
    config EEPROM, I read a bunch of garbage data form the FT245BM after
    start-up.
    Without the pull-down option the FIFO is (as expected) empty after
    start-up.

    I have the following setup:
    - FT245BM connected to a ATmega64
    - Configured as bus powered device (500mA)
    - VCC and VCCIO are (for now) 5V
    - VCC for the ATmega64 is switched using a IRLML6402 P-MOSFET

    I think a have found what causes the FIFO state/content to be corrupted.
    FTDI write in one of the appnotes that reading from the FIFO while it is
    empty or writing to it while the TX buffer is full may lead to data
    corruption.

    Using a scope i see that during init of the FT245BM (while PWREN is still
    high) the pull-ups of all interface pins (D0-7, WR, RD, TXE, RXF, SI) get
    turned on and off 3 times!?

    As this only happens with the pull-down option enabled, my best guess is
    that the edges on RD corrupt the internal state of the FIFO.

    The only help I got from FTDI is that the pull-ups are initially turned on,
    then the EEPROM is read and if the pull-down option is enabled they should
    get turned off until PWREN goes low.
    (I guess after they noticed that i'm "only" a hobbyist they stopped
    responding ...)


    Has anyone here used the pull-down option with success?


    Thanks in advance,
    Bertolt
    --
     
    Bertolt Mildner, Jul 13, 2004
    #1
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