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Comms problems with TTL pins

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  • Comms problems with TTL pins


    I'm having problems communicating with my u-LCD 1Mb at the TTL level (using the 1k series resistors too) but no problems at all when comms is with the u-USB, so I know the unit is functioning correctly.

    I initially ran it from a PIC (tried inverted/true polarity, various delays, etc,) but got nowhere so went back to basics and tried with Docklite via a DS276 serial/TTL converter chip from my laptop USB/RS232 converter. I've confirmed the port is good with a loopback from the DB9 at the adapter and also from the TTL side of the DS276, but nothing happens with the LCD when the test is repeated fully wired (cycling power to the LCD each time).

    I've hard soldered in my u-USB module - do I need to remove it in order to use the TTL comms or are they compatible and the cause of my problem is elsewhere?

    Any help appreciated.


  • #2

    Hi Bill,

    The problem is the uUSB Tx/Rx lines would be "hogging" the Serial line. If you can remove the uUSB and socket it so that when using the normal serial lines you can take the uUSB module out. I'm hoping you're going to be able to remove uUSB without causing you too much grief.
    Let us know how you go.


    • #3

      I know it is too late now, but it is one of the reasons we came up with the 4d-USB-5V Kit of Parts #16456

      I hope this message will help others

      Don McKenzie

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      These products will reduce in price by 5% every month:


      • #4

        Thanks Don,

        Looks like a good idea, I'll get a few next order. I think the addition of sockets for the uUSB on the other products would also have been beneficial given the small cost involved, but the above arrangement is more versatile and lower in profile.

        Atilla, I'll PM you regarding the uLCD situation.

        Kind regards,


        • #5

          i've try to interface on an serial port of thePC with an MAX232 but it need a couple of transistor to pull down below 0.8V the RX line before it works


          • #6

            There's a "typical connections" diagram here:
            It might come in handy.