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Data communication between ADS1298 and MSP430

Weng Kou Chan
Expert 1215 points
Other Parts Discussed in Thread: MSP430F2274, ADS1298, SN74AVC4T774

Hi 

I am trying to use the MSP430F2274 chip to read the data output from the ADS1298.

However it was not successful, and I am assuming the cause of the problem is the difference logic levels used from the chips.

How do I solve this problem please?

 

 

Here is my configuration

ADS1298, Analogue power: 3V Digital power 1.8V

MSP430F2274 Logic high: 3V/3.2V

(It is the MSP430F2274 embedded on RF2500, so I power it up by the USB)

Thanks all

  • 0
    TI__Guru**** 181001 points

    Hi Weng Kou Chan,

    If this is a logic level issue, the easiest way to resolve your problem is to power the ADS1298 digital side from the same 3.3V supply that you use on the MSP430 side.  Or from the same 3V supply you use for the analog rail.  Is there some specific reason why you cannot do this?  If so, you may need to consider adding a level shifting circuit - maybe something like the SN74AVC4T774 would be in order. 

  • 0 in reply to Tom Hendrick
    Expert 1215 points

    Thank you for the reply, and really sorry that i have left it so long.

    I am not too sure whether I can use 3.3V supply to ADS1298, since it then outputs around 3.3V.

    Looking at the datasheet for MSP430F2274 http://focus.ti.com/lit/ds/symlink/msp430f2274.pdf, Page 30 I don't know whether I interpret it correctly. The max of  the input threshold voltage is 2.25V, so does it mean I must use a logic shifter to connect them?

  • 0 in reply to Weng Kou Chan
    TI__Mastermind 46290 points

    Weng Kou Chan,

    If you still have the emails we exchanged some weeks ago on this matter I think we touched on this. The parameters you're looking at are triggering thresholds. So the MSP430 is going to interpret a high at min 1.35V or at max 2.25 volts. So, you're guaranteed to get a logical high triggered on the MSP430 since 3.3V will well exceed the 2.25 V max requirement.

  • 0 in reply to Kevin Duke
    Expert 1215 points

    Yes, I still have the email, and I just finished my exams and came back to work on this, so I would like to ask again before I may do something silly and burn the chip down.

    By the way, have you had a chance to see my circuit board please? I remember you said you have a concern on the ground signal route.

  • 0 in reply to Weng Kou Chan
    TI__Mastermind 46290 points

    Weng Kou Chan,

    I've not taken a look at the layout since the email you sent me explaining the incorrect pin-out on your schematic. I'll try to give it a look later this afternoon and get some feedback to you. Regardless, the state of the layout/schematic you sent me does not have the ADS1298 or MSP430 operating on the same logic levels, and it's something you're going to want to address either by changing the supplies to the 1298 or using a logic shifter as Tom mentioned.

  • 0 in reply to Kevin Duke
    Expert 1215 points

    I have tried to use DVDD = 3.6V for ADS1298 and has no success, in fact, it was getting worse. 

    Before I left it and did my exams, I have confirmed it I could write into the register, and I verified this because I can see the 2.048MHz clock signal from the ADS1298.

    However, I used the same hardware set up, same code that I sent you, it didn't show me the clock signal any more, and I have been trying to find the problem until today. 

     

    Can you give me some advices or steps to help me out with diagnosing a problem please?