Having trouble using PIC as SPI driver for Hittite PLL


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  1. #1
    Join Date
    Aug 2009
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    13

    Default Having trouble using PIC as SPI driver for Hittite PLL

    I'm working on a project where I'm using a PIC18F14K50 to drive a Hittite HMC704LP4E frequency synthesizer via SPI in HMC Mode. I'm trying to make sense of the Hittite documentation. Am I understanding it correctly that I DON'T send whole bytes to the Hittite chip, just strings of bits (in non-multiples of 8)? I don't have an eval board to work with, and I'm just the "code guy." Does anyone else have experience working with these?

  2. #2
    Join Date
    Oct 2005
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    Sweden
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    3,516

    Default Re: Having trouble using PIC as SPI driver for Hittite PLL

    Hi,
    I don't have any experience with these chips but I briefly looked at the datasheet. Indeed, the HMC mode does look "strange".

    If you're using the bitbanged routines, ie SHIFTOUT/SHIFTIN then I don't think there shold be any problems shifting out/in any number of bits. However if you're using the MSSP module then HMC mode doesn't seem to be a good fit.

    Is there a specific reason for selecting HMC mode? It seems easy enough to just select Open mode instead, in which case a transaction is 32 bits (24 + 5 + 3), if I'm reading the datasheet correctly. That mode looks a lot easier "to do" than HMC mode.

    /Henrik.

  3. #3
    Join Date
    Aug 2009
    Posts
    13

    Default Re: Having trouble using PIC as SPI driver for Hittite PLL

    Hm... you might be right. I completely over looked that. Let's see if it works!

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