Need help on long distance (>1.5m) SPI bus.

Discussion in 'General Electronics Chat' started by rexma, Dec 8, 2008.

  1. rexma

    Thread Starter New Member

    Dec 8, 2008
    2
    0
    the problem is, the spi device is far away from the mcu. it's quite unstable.

    3.3V MCU SPI clk/data --------- >1.5m track---------> device

    someone suggested me to use a buffer(74hct245) to convert 3.3v signal to 5V and add pull-up resistors.

    3.3V MCU SPI clk/data -->74hct245-->5V pull-up res --> device


    i really need more advice.
    thx. :)
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,137
    1,786
    How fast is the clock that you are using. The use of a driver chip with more current drive will help on a long cable which looks like a capacitive load. Using a Schmitt Trigger on the input will help also.

    A better solution might be to use a differential line driver and receiver. Proper termination of the transmission line will also help to control reflections.
     
    Last edited: Dec 9, 2008
  3. rexma

    Thread Starter New Member

    Dec 8, 2008
    2
    0
    thx for your reply. :)
    I use a schmitt trigger buffer NL27WZ17. And it works!
    http://www.onsemi.com/pub_link/Collateral/NL27WZ17-D.PDF
     
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