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SPI Interfacing circuit between two microcontrollers

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vsrinivas
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2009/05/06 05:19:39 (permalink)
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SPI Interfacing circuit between two microcontrollers

Hi sir ,

I'm communicating two microcontrollers (pic8722) using SPI communication .One microcontroller as a Master and one as a Slave.But here my doubt is on the  communication lines pull up and pull down resistors are required or not.
               
                          ON SDI
                                SDO
                                 SCLK
                                  SS
On these four pins pull up & down resistors required or not .If required please tell me the values of that resistors . 

    
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    jmag99
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    RE: SPI Interfacing circuit between two microcontrollers 2009/05/06 06:29:14 (permalink)
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    These lines will be actively driven by the SPI master except SDI which is open-drain when the spi module is not selected with SS and driven by the slave when SS is low.  They do not require pull-up resistors.  Sometimes I use pull-ups on the chip select lines to prevent activation during startup.  The hardest part of this setup is getting the SDI timing right.
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    vsrinivas
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    RE: SPI Interfacing circuit between two microcontrollers 2009/05/06 21:51:30 (permalink)
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    Thanks  for giving reply

         Actually i use pull up resistors on SDI SDO & SS Lines. 
                             PULL down resistor ON SCLK line. It's correct or not i don't know.But in one Analog devices slave circuit i saw like this .

      In which situation pull up and pull down resistors are required and which situation they are not required.
          pls  give me brief explanation.

    And tell me the calculation of pull up and pull down resistors mathematical calculation for Communication  lines and I/O Lines separately.
    #3
    prinz3nroll3
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    RE: SPI Interfacing circuit between two microcontrollers 2009/05/12 01:47:30 (permalink)
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    Hello,
    i use always an pullup @ nCS.
    The pullup resistor is 10k.
    i ve connect an optional port from slave to master.
    this port set the slave always if he is ready to send data.

    greetings
    #4
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