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SPI puzzle

Discussion in 'Oshonsoft' started by camerart, Nov 23, 2016.

  1. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    I guess you know NSS is /CS .?? [NOT CS]

    Where is the RESET connected.?

    Are the DIO pins allowed to 'float' the datasheet should tell you.

    As you say the PCB requires a 3.3v supply.

    I usually add a 10k pull up on MISO

    E


    EDIT:
    How are you planning to get the 18F2431 PIC to communicate via RS232 to the other PIC.????
     
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi C,
    This is a clip from my circuit showing the SPI and 74HC125 level shifter.

    There are 100R's in series with the three PIC output pins to the HC125.
    The logic +5v High input current should be limited to < 20mA when powering the HC125 with3.3v.
    [I have sometimes used the HC without the 100R's with no problems, but I would not recommend this way]

    Note the 10k pull up for MISO.

    E
     

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  3. camerart

    camerart Member

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