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ADS7952: ADS7952 / Write/Read sequence in Manual Mode

S.Satoshi
Guru 21685 points
Part Number: ADS7952

Hi,

Please advise me about SPI of ADS7952.

 

Here is the expectation of Write/Read sequence after Power-up. Is it correct?

 

-> Power-up (adhere to "Power Supply Recommendations")

                     (Interval : >10mS)

                            -> 1st Frame         Write [Mode: Manual, MUX: Ch1]

                                                        Read [invalid]

                             -> 2nd Frame        Write [Mode: Manual, MUX: Ch2]

                                                        Read [12bit conversion result of Ch1]

                             -> 3rd Frame         Write [Mode: Manual, MUX: Ch3]

                                                        Read [12bit conversion result of Ch2]

 

 

On the customer's system, we found the sequence seems necessary to put 1st Frame as "Dummy" for reading out a valid data as below. Could you let me know your considerations?

 

              -> Power-up (adhere to "Power Supply Recommendations")

                     (Interval : >10mS)

                            -> 1st Frame         Write [Mode: Manual, MUX: ---] ---> Dummy

                                                        Read [invalid]

                             -> 2nd Frame        Write [Mode: Manual, MUX: Ch1]

                                                        Read [invalid]

                             -> 3rd Frame         Write [Mode: Manual, MUX: Ch2]

                                                        Read [12bit conversion result of Ch1]

Best Regards,

Satoshi / Japan Disty

  • 0
    TI__Genius 16890 points
    Hello Satoshi-san,

    The first sequence should be the correct one according to Figure 49 of the datasheet.
    What are the actual values they are setting the control register to?

    -> Power-up (adhere to "Power Supply Recommendations")
    (Interval : >10mS)

    -> 1st Frame Write [Mode: Manual, MUX: Ch1] (what hex value are they sending to the register?)
    Read [invalid]

    -> 2nd Frame Write [Mode: Manual, MUX: Ch2] (what hex value are they sending to the register?)
    Read [12bit conversion result of Ch1]

    -> 3rd Frame Write [Mode: Manual, MUX: Ch3] (what hex value are they sending to the register?)
    Read [12bit conversion result of Ch2]

    Mike
  • 0 in reply to Michael Stout
    Guru 21685 points

    Hi Mike,

    Sorry for my delayed response. Please let me ask again if my understanding is correct.

    From Fig.1 in datasheet, the input data at Frame n may be output at Frame n+2, because Mux Ch change is started in the middle of Frame n and it stride over Frame n+1. Can you please give your opinion about this?

    Best Regards,

    Satoshi / Japan Disty

  • 0 in reply to S.Satoshi
    Guru 21685 points

    For your additional information, my customer is evaluating ADS7952 actually and confirm following result.

    • When the Mux ch is not changed, the input data at Frame n is taken at Frame n+1
    • When the Mux ch is changed, the input data at Frame n is taken at Frame n+2

    Thanks

  • 0 in reply to S.Satoshi
    TI__Genius 16890 points

    Hello Satoshi-san,

    When you write to change the mux at n the data should come out at n+1.  Please see figure 50.  This shows that for example in frame n the device will be sending out the conversion data for frame n-1.  Also in frame n you re programming for frame n+1.

    Mike

  • 0 in reply to Michael Stout
    TI__Genius 16890 points
    Hello Satoshi-san,

    The datasheet is unclear on this. It does look like the data comes out on n+2. Please see this post:

    e2e.ti.com/.../1077037

    Mike