Cascading 2 or 3 SPI devices

Discussion in 'Embedded Systems and Microcontrollers' started by PICfan, Feb 3, 2011.

  1. PICfan

    Thread Starter New Member

    Jan 14, 2011
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    0
    Cascading SPI devices to PIC 16F/18F
    Hello All,
    When two devices are Cascaded to a uC via SPI is it possible to send seperate commands to each device without having to control CS(SS) on each device.

    I am a little confused with the SPI Cascading description. does the word length increase to 16 bits when two devices are cascaded, with the first 8 bits being sent going to the second device(as it would get shifted out of first device) and then the second 8 bits then going to the first device in the chain?
    Or would the first 8 bits get shifted in to both devices and then when second 8 bits is sent it then gets shifted into both devises? (this not what i want).

     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
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    Hi I posted this to day in some other trhead.
    http://ww1.microchip.com/downloads/en/devicedoc/spi.pdf
     
  3. PICfan

    Thread Starter New Member

    Jan 14, 2011
    2
    0
    Hi t0

    I had read this info from Microchip, .
    It shows how to use a PIC for SPI interfacing to one or more devices by using the Chip Enable(SS) pin.

    But this does not answer my questioni.
    Perhaps i was not specific enough.

    Is there another method to cascade two or more SPI devices with out using the (SS) pin?

    Thanks
     
  4. t06afre

    AAC Fanatic!

    May 11, 2009
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    The SPI follows the principals of a buss system. Many can listen, but only one can talk at the same time. So I am quite sure the answer will be no. But you should explain exactly what you try to do with drawing and some more info. Like what PIC are you using and what is the SPI device. Only then we can say for sure
     
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