• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 45 subscribers
  • Views 113 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS124S08: Timing Parameter Violation Question for START/SYNC and xDRDY

Darren (FAE)
Expert 5483 points
Part Number: ADS124S08

Another ADS124S08 Question Slight smile

About parameter "tsu(STDR)" from the Datasheet. If this parameter is violated, what will be xDRDY operation?
(Start = H just before xDRDY = L)

If Start = H just after xDRDY = L, what will happen...?

*I think Figure 4 at tsu(STDR) point from the Datasheet might help with this question.
START/SYNC going High again just before xDRDY goes Low. What would happen...?
And what would happen if START/SYNC was HIGH when xDRDY goes low?

  • 0
    TI__Guru** 112745 points

    Hi Darren,

    The tsu(STDR) timing parameter is specific to the STOP action and decode relative to the DRDY.

    Darren (FAE) said:
    About parameter "tsu(STDR)" from the Datasheet. If this parameter is violated, what will be xDRDY operation?
    (Start = H just before xDRDY = L)

    If the START was low and then goes high the conversion will restart cancelling the previous conversion.

    Darren (FAE) said:
    If Start = H just after xDRDY = L, what will happen...?

    In this case a new conversion will begin immediately and DRDY will go high.

    Darren (FAE) said:
    *I think Figure 4 at tsu(STDR) point from the Datasheet might help with this question.
    START/SYNC going High again just before xDRDY goes Low. What would happen...?
    And what would happen if START/SYNC was HIGH when xDRDY goes low?

    You might be overthinking this a bit.  DRDY signals an end of conversion.  The START/SYNC pin determines whether a conversion should start (or continue) or stop.  The issue here with tsu(STDR) is the decode time to STOP an ongoing (continuous) conversion relative to the update period for when the conversion completes, then updates the output buffer and starts the next conversion.  I think it may be more beneficial to look at the Operating Flow Chart in Figure 82 on page 58.  It may also be helpful to review section 9.4.4 regarding Conversion Modes.

    There is a decode time requirement for the STOP, however there is no requirement for the START.  You can think in terms of the the STOP setting an internal flag where the state machine allows for the current process to complete.  You can think of the START in terms of an interrupt where the action interrupts the current process and resets the state machine.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Expert 5483 points

    Hi Bob, 

    I'm understanding the question better now.

    Assuming we begin with START = H.
    We are getting conversions.

    If START goes from High to Low, then xDRDY is asserted. If START goes High before xDRDY goes LOW (tsu(STDR)-time after START goes LOW), then the state machine is reset and we go right back to starting a conversion. 

    So will xDRDY automatically be pulled LOW with START going HIGH then?

    I have another Question come in...the Datasheet describes how to do a CRC check on the Data.
    1) With just 24-bits of Data, it says you need to left-shift 8-bits to get 32-bits.
    2) If you use the STATUS byte, so 32-bits, you still need to left-shift, right? (Basically getting rid of any STATUS data)
    3) Could you tell me the expected CRC-value for STATUS = 0x00 and DATA = 0x000000?

    I can't find an online calculator for the method stated in the Datasheet, and I am unsure how to do the calculation by hand...
    And the customer is asking for the CRC-value.

    Darren

  • +1 in reply to Darren (FAE)
    TI__Guru** 112745 points

    Hi Darren,

    If the START transitions from high to low the ongoing conversion will completed and DRDY will make the transition from high to low to signal the conversion has completed and the conversion result is ready to be read from the ADC.

    If START transitions from high to low then back to high before the ongoing conversion completes, the conversion will be restarted.  When START goes high, so will DRDY ( or stay high if DRDY is already high).  See figure 84 in the ADS124S08 datasheet.

    Darren (FAE) said:
    So will xDRDY automatically be pulled LOW with START going HIGH then?

    No, DRDY is pulled high when the START pin goes high.

    Regarding CRC calculation I have written a general Data Integrity application note that discusses CRC.  Also there is a CRC calculator tab in the ADS1xS0x calculator tool on TI.com.

    Best regards,

    Bob B