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MSP430F229<->ADS1158 SPI Interface

Annie Manuja
Prodigy 40 points
Other Parts Discussed in Thread: MSP430F5529, ADS1158

Hello All

I am new to MSP430F5529 and ADS1158 and SPI as well. As per my application, I am using 3 ADS1158 as slaves and one Master that is MSP430.

I would like to know if I can connect all three ADS with one SPI port on MSP430 and use chip selects from other ports/GPIOs to control these slaves or is it better to hook up all three ADS units on 3 different SPI modules?

Thank you

 

 

  • 0
    TI__Intellectual 1600 points

    Hi Annie,

     

    You should be fine connecting all 3 ADS1158's to a single SPI port.  Of course, you will need a dedicated GPIO pin connected for each ADS1158 to control the Chip Select (CS).  Depending on your application, you may also want a dedicated digital pin to each device's Data Ready (DRDY) pin.   That will allow you to respond to each individual data converter as it finishes it's conversion.

     

    One thing  to consider, though, is the data rate that you will take data from the ADS1158's.  The SPI port on the MSP430 will need to run at three times the ADS1158's data rate to account for all three devices.   I'm not familiar with the speed of the SPI port or how you will use the data converters, but it should be a simple calculation to know if you can get data from all three devices fast enough.

     

    Rudye

     

  • 0 in reply to RudyeM
    Prodigy 40 points

    Thank you so much for your reply.

    MSP430 MCLK is running at 19.2MHz. ADS1158 (slave) on SPI Interface can maximum run till 16MHz (master clock period). If I plan to run ADS1158 at 6MHz, can I use SMCLK of MSP430 to run ADS1158 or do I need another crystal oscillator to run ADS1158 independently? What is a better frequency plan in case of interfacing MSP430F5529 with ADS1158 on SPI?

    Thank you

    Ann

  • 0 in reply to Annie Manuja
    TI__Intellectual 1600 points

    Hi Ann,

    You should be able to use the SMCLK at 6MHz from the MSP430 to clock the ADS1158.  I don't think you'll need to run the ADS1158 independently with an x-tal as long as you configure it for an external clock as described on page 15 of the datasheet.

    Is there a better frequency plan?  For the ADC, you should be considering the data rate and frequency response you need rather than the interface to the MSP430.  These are described on pages 15 and 16 in the datasheet.  If a 6MHz clock, will give a data rate sufficient for your application, then it is a good frequency plan.  There is a lot of flexibility in the MSP430 clocking scheme and the SPI interface to account for whatever data rate you need.

     

    Regards,

    Rudye

     

  • 0 in reply to RudyeM
    Prodigy 40 points

    Hello Rudye

    Thanks for your reply again. Its a data logging kind of application. Can we run MCLK and SMCLK at same frequency? What if we run ADS and MSP430 at same frequency say 16MHz? The SPI port has 3 slaves on one SPI port of MSP, do you think capacitance can be an issue? If I run MCLK at 16MHz or 19.2MHz, what maximum frequency I should run the SCLK at? Also, are there any recommendation to select crystal oscillator for MCLK, I mean does it need to XO or TCXO or just a tuning fork?

    Thanks a lot

    Annie

  • 0 in reply to Annie Manuja
    TI__Intellectual 1600 points

    Hi Annie,

    Yes, you can run the MCLK and the SMCLK at the same frequency.  16MHz should be a good choice.  I don't think 3 SPI devices on one port of the MSP430 should be a problem.  You can consult the MSP430 datasheet for their port drive capability and add buffers if necessary.  3 devices should be fine, though.  I don't know what type of oscillator is recommended for the MSP430.  You might consult an MSP430 EVM schematic to see what is being used there.  Or, you could post your question to one of the MSP430 forums to see what others are using.

     

    Good luck with your data logging application!

     

    Rudye