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Thema: RS232 pinout and connection to FT232 based USB adapter

  1. #1

    Standard RS232 pinout and connection to FT232 based USB adapter

    Hi,
    here is a summary how to connect our NAS to an USB/RS232 TTL adapter.

    If it is a FTDI FT232R based adapter like this one from ebay (here)

    with this circuit diagram


    set the Jumper to get VCC from target:
    J1/1-2 and J4/2-3

    and connect these signals:
    NAS - Adapter connection
    GND/ 5 - GND/10
    VCC/10 - VCC/2 (3.3V)
    Rx/ 2 - TXD/8
    Tx/ 3 - RXD/6

    The 4220 232 pinout

    Always connect the adapter to the target before connecting the USB cable!
    Be aware of electrostatic discharge!

    There is no protection on the NAS and the signals directly lead to the CPU.

    You could use some old RS232 flat cables for a PC slot but most of them don't have a wire for pin 10 and only have 9 wires. As we don't need Pin 1 you could plug pin1 to 10...

    Regards, HWguru
    Angehängte Grafiken Angehängte Grafiken
    Geändert von HWguru (17.01.2010 um 19:00 Uhr) Grund: link updated

  2. #2
    Ampuj4
    Gast

    Standard Nas protection

    Why not add loop isolator for nas to prevent electrostatic discharges ?

  3. #3

    Standard

    Always connect the adapter to the target before connecting the USB cable!
    Be aware of electrostatic discharge!
    1. The NAS power supply has no connection to earth. Therefore the whole NAS is floating because of capacitance inside the psu. In worst case there is 110V between NAS and PC/Adapter. If you discharge that through the NAS pins you likely destroy it.

    2. In a home environment you cannot avoid electrostatic charges and you have to be careful when touching electronics. This applies to any kind of hardware.

    If you follow my guide you will be safe.

    HWguru

  4. #4

    Idee

    Hi there...

    Just two small questions.


    1) I have the V1.2 board. Where can I find the pinout for it?
    It seems to have a double sided surface mounted connector pins, not through hole.




    2) I will be using a USB/TTL converter based on the FT232BL. --LINK--
    I'm planing to get 3.3V from the NAS Vcc. Will this configuration work ok?


    Also, could anyone upload the files I will need to upload to the NAS to flash it?
    RaidSonic is taking forever to answer my e-mails.

    Thank you in advance...



    Bill
    Geändert von billseldon (06.11.2009 um 19:37 Uhr)

  5. #5

    Standard

    Hi,

    1) Yes, J2 is the connector we are talking about, no matter if it is through hole or not.

    2) this adapter (FT232BL) seems to be a 5V version - needs 5V from VCC
    The chip is capable of working with an IO voltage 3.3V but the PCB does not support this.
    So you need to modify it like shown here:
    1. carefully lift Pin 13
    2. cut trace at the board edge
    3. connect Pin 13 with the right side of the resistor (near PWREN)
    4. connect (solder) the USB Power jumper

    If you search at the forum you will find everything else.

    Please: this thread is about "RS232 pinout and connection to FT232 based USB adapter" nothing else. New question - new thread please.

    Regards,
    HWguru

  6. #6

    Standard

    So, if I understund corectly, by doing this mod on the PCB, you are driving pin13 (VCCIO)
    with 3.3VDC from the NAS, an you still let 5VDC from the USB port go to pin3 + pin26 (VCC).

    Right?

  7. #7

    Standard

    So, if I understund corectly, by doing this mod on the PCB, you are driving pin13 (VCCIO)
    with 3.3VDC from the NAS, an you still let 5VDC from the USB port go to pin3 + pin26 (VCC).

    Right?

  8. #8

    Standard

    Hello billseldon,
    you are absolutely right!

    This ensures that the serial pins are driven with VCC (3.3V) of the NAS and that the adapter stays connected independant of the power status of the NAS.
    On the other hand the FTDI chip needs 5V Supply and this is taken from the USB port.

    (has been tested by a user some times ago - the original board did not work)

    HWguru

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