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msp430 spi digital pot problem

arun j2
Intellectual 350 points
Other Parts Discussed in Thread: MSP430F5529

Hi,

    I am using msp430f5529 controller, I am having one i/o line called digital pot which is used to control the spi communication,but i am not getting how to use the pot , can any one explain me how to use this pot and steps to be followed . I am using spi communication between msp430f5529 and cc3000 module.

Regards

Arun j

  • 0
    Intellectual 740 points

    Which "pot" are you referring to? Could you please be a bit more specific? To my knowledge, neither the F5529 EVMs nor the CC3000 have a digital potentiometer included.

  • 0 in reply to Michael_M
    Intellectual 350 points

    Hi Michael,

                  Its CS_DPOT output pin from msp430f5529.

  • 0 in reply to arun j2
    Intellectual 740 points

    That's clearly the signal name of your specific (custom?) circuit. What's the name of the digital potentiometer? To which pin of your MSP is connected? Without any details it's impossible to help.

  • 0
    Guru 227245 points

    An I/O line called „digital pot“ likely is the chip select line for an external chip with SPI interface.

    SPI is a bus. You can connect any number of devices to it. Which one you are talking to, depends on which one gets its chip select (CS) input low. All others remain passive. So if you pull this line low (and all others like the one for the CC3000 high), you can talk to the pot through SPI. But how to program the POT (and whether there is one at all) depends on your application. See the schematics of your PCB and the device datasheet (of the POT) for details.

  • 0 in reply to Michael_M
    Intellectual 350 points

    Hi Michael_M,

                  Its connected to P2.5 pin of msp430f5529 controller as the output pin.

  • 0 in reply to arun j2
    Guru 227245 points

    It is unimportant which MSP pin is used to output the chip select signal. The question is: where does it go to? Is there a device connected at all that is selected with this signal? Which one?

  • 0 in reply to Jens-Michael Gross
    Intellectual 350 points

    Hi Jens-Michael Gross,

                      chip select line along with MISO and MOSI are connected to AD5260 digital pot.

  • 0 in reply to arun j2
    Guru 46710 points

    arun j2 said:
      chip select line along with MISO and MOSI are connected to AD5260 digital pot.

    CS input of particular digital pot is "active low" . So to activate SPI of digital pot you shall set logical "0" on msp430 output pin conneted to !CS pin of digital pot.

  • 0 in reply to arun j2
    Guru 227245 points

    Okay, now we can proceed.

    This pot is fairly simple. Configure the PSI for 3-wire master, MSB first (!). Configure the CS pin as GPIO output, initially high.
    Pull CS low, then send the desired pot position n to the pot by writing it to TXBUF.. When done (check the UCBUSY bit for completion of the transfer). Then pull CS high again. That’s it.

    The pot will set the wiper to n/255 of its maximum value. That’s it.
    You can daisy-chain multiple pots by connecting all their CS lines together, and the CO of one to CI of the next. Then you send multiple bytes (as many as there are daisy-chained pots). The first byte after CS=0 goes to the last pot in the chain, the nth goes to the first. Then do CS=1. At this moment, all will update the wiper position.

  • 0 in reply to Jens-Michael Gross
    Intellectual 350 points

    Hi Jens-Michael

                   In data sheet of AD5260 which topic i need to refer in order to find  the  procedure given by u.

  • 0 in reply to arun j2
    Guru 227245 points

    Theory of Operation -> Digital Interfacing/Daisy-Chain operation.
    Note that the drawing with the A0 bit in the shift register is for the dual AD65262. Operation is slightly different then.
    Also note that the datasheet talks about “4-wire operation”, but is counting the CS signal as 4th wire. This is not to be confused with the MSPs 4-wire mode. Select 3-wire mode in the MSP. The 4th wire is done by software on a GPIO and its usage depends on the high-level protocol of the slave. (and therefore cannot be done by the SPI hardware)

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