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SPI problem

Discussion in 'Microcontrollers, Programming and IoT' started by scancool, Oct 5, 2010.

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  1. scancool

    scancool

    5
    0
    Oct 5, 2010
    I want to connect 20 shift registers to a SPI BUS but after 10 shift register the CLK gets a lot of distortion plus the spi bus has a distance of 6 feet, is there any type of buffer the is not too small to solder that I can use, I'm running a 20Mhz clock.
     
  2. LTX71CM

    LTX71CM

    182
    0
    May 23, 2010
    The SPI bus is running at 20MHz over six feet or your microcontroller is running at 20MHz and your SPI bus happens to span six feet?
     
  3. scancool

    scancool

    5
    0
    Oct 5, 2010
    the SPI expand six feet, and the clock is pulsing at 100ns I slow it down but I have to make it faster and I can cause the signal gets distorted, any idea what type of buffer I can use or what I can use to make it a perfect square wave?
     
  4. LTX71CM

    LTX71CM

    182
    0
    May 23, 2010
    What's your operating voltage?

    The problem is speed, distance and fanout. Check your controller's datasheet for drive current and then check that against the shift register datasheet inputs.

    Is everything mounted on a PCB, with wire? Any shielding involved? Any form of noise reduction?

    This is for an LED sign I presume?
     
  5. scancool

    scancool

    5
    0
    Oct 5, 2010

    everything is mounted on 6 PCBs, and is to drive LEDs, is there any type of buffer I can use to increase the clock signal ? the clock signal is 3.3V
     
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