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question about open-drain-port

Discussion in 'Electronic Basics' started by made, Apr 18, 2004.

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  1. made

    made Guest

    Hy

    I´d like to connect a lcd (ttl 5V ;generic) to my microcontroller(cmos
    3.3V, at91eb55).
    I understand that it would be a good idea to use a open drain output
    to drive the lcd. But what happens if I set the io-pin to input mode to
    read the status register from the lcd ? Can the lcd drive the voltage
    level ?


    .....+5V.....
    .....|.......
    ...._|_......
    ....|R|.......
    ....---.......
    .....|........
    .....|..._____
    .....|...|....|
    --------|.LCD|
    .........|....|
    .........|....|
    .........------
     
  2. if the lcd has TTL input, you can drive the lcd with 3.3V without a
    open-drain! because the Vih (Input Voltage High) begin at about 2V! and
    certainly the microcontroller is input 5V tolerant!
    excuse me for my english!
     
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