Minimum lines for SSP


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  1. #1
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    Default Minimum lines for SSP

    EDIT:

    Nevermind.

    I just found the SPI Daisy Chain connection in the datasheet. That means I can keep using 4-strand telephone wire.


    How fast can MSSP transmit at 64MHz?

    I was initially planning on using USART at 115,200, but I'd like to know if it's worth the hassle to switch over to MSSP.

    Robert
    Last edited by Demon; - 19th December 2014 at 19:12.

  2. #2
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    Default Re: Minimum lines for SSP

    I had to share GND when using USART between 2 PICs.

    Do I also have to share the GND line between 2 PICs when using MSSP in Daisy Chain?

    I'd really like to avoid having to run another cable underground and was hoping I could get away with just CLK, DATAIN, DATAOUT and SS in Daisy Chain.

    Robert

  3. #3
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    Default Re: Minimum lines for SSP

    Hi Robert,
    The SPI master Clock can run as fast as FOsc/4, ie the same as the instruction clock which, at 64MHz, is 16MHz. ~140times faster than 115kbaud.
    The problem is that you're most likely not going to be able to feed the MSSP module with data at fast enough to keep an overall speed anywhere close to 16Mbit. (And it probably won't work reliably over any sort of length of telephone wire....)

    The slowest selection for the SPI Clock is FOsc/64 which would be 1MHz in your case - 8.7 times faster than 115kbaud.

    /Henrik.

    EDIT: Yes for a simple direct Connection they must share the same reference. There are of course things like RS485, optical transmission etc etc but again, for a simple direct Connection they need to share the same GND potential.
    Last edited by HenrikOlsson; - 19th December 2014 at 19:30.

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