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ADS7950: Always getting CH0 data on SDO pin in AUTO1, AUTO2 and manual mode.

Vamsi M75
Prodigy 30 points
Part Number: ADS7950

Hi

We are having issues in getting different channels data using AUTO1 mode.

We configured this part to AUTO1 mode for CH0,1,2,3 but we are not able to get ay data other than CH0.

FYI we tried the same for Manual mode also but it is acting the same way.

Here is the bit flow we are using on SDI

1. (CS High to LOW)  0001 0000 0000 0000 // Enter in Manual Mode at Power ON

2. (CS High to LOW)  1000 0000 0000 0000 // Enter to program AUTO1_PRGM REG

3. (CS High to LOW)  0000 0000 0000 1111 // Configure CH0,1,2,3 in AUTO1_PRGM REG

4. (CS High to LOW)  1001 0000 1100 0000 // Enter and configure AUTO1_PRM REG for CH0,1,2,3

5. (CS High to LOW)  0010 1000 0000 0000 // Enter into Auto1 mode

6. Rep Step5 multiple times to get multiple channel data

But on SDO we get data as 0001 xxxx xxxx xxxx always. As you could see we always get CH0 data.

Please help, I think we are not following the sequence properly.

Thanks

Vamsi

  • 0
    TI__Mastermind 25020 points

    Hello,

    From your post, it seems you are correctly programming the sequence channels, steps 2 and 3

    But step 4 does not seem correct. The first four bits, DI15-12 should be 0010 to select Auto 1 Mode. The command you are entering, highlighted below is actually to program auto 2 sequence.

    4. (CS High to LOW)  1001 0000 1100 0000 // Enter and configure AUTO1_PRM REG for CH0,1,2,3

    Please refer to the below table from the datasheet for how to enter Auto1 mode after configuring the sequence.

    Regards, Cynthia

  • 0 in reply to Cynthia
    Prodigy 30 points

    Hi Cynthia

    Actually we tried fixing that and also in manual mode with first 4 bits as 0001 followed by appropriate sequence but no matter what the mux is not switching the channels.

    FYI here are some settings and voltages that we currently have, Could you please check them:

    1. VREF = 1.85V

    SDI, CS, SCK are at 0 to 5V logic family

    VDD and supply at 3.3V

  • 0 in reply to Vamsi M75
    TI__Mastermind 25020 points

    Vamsi,

    This device is meant to be used with a 2.5V external reference, at your current level you are not meeting the minimum spec outlines for the device.

    When debugging, to make sure that the digital communications are correct, Connect a scope to the digital lines can elp visually verfiy that is expected to and from the device is actually what is going on. you can use this scope shot to compare versus the table to make sure it is correct. make a special note of the bit DI10, as this should be 0. if not then the channel will always be the lowest channel count, in your case, channel 0. This can also help verify the digital timing in case there is any issues with that.

    Regards, Cynthia

  • 0 in reply to Cynthia
    Prodigy 30 points
    Hi Cynthia

    Tried changing vref to 2.5V

    Still not able to change the channel on SDO.

    FYI - we are verifying this on OSCOPE.
  • 0 in reply to Vamsi M75
    TI__Mastermind 25020 points

    Hello,

    Would you please share a scope shot, including the digital lines, SCO, SDI, CS, SCLK. Please include more than one CS frame.

    Have you verified your hardware? Are all power supplies at correct values and such, are connections correct.

    Is pin MXO connected to pin AINP on the device? or connected through a common input driving circuit?

    It would be best to use a known DC input value for debugging, but different values at each input. for example, Ch0 = GND, Ch1 = 1V, and so on.

    Once manual mode is working correctly, then it should be easier to get auto1 mode working.

    When in manual mode, with each SDI command, the desired channel sampled needs to be selected, by chaning DI10-DI7.  Note that you will not see this channel data out unto two frames of CS falling edge later.

    For auto 1 mode, looking at your steps from your original post,  please try the following:

    4. (CS High to LOW)  0010 1000 0100 0000 // Enter and configure AUTO1_PRM REG for CH0,1,2,3 ( enable programing, channel counter increments, 2xVref range, normal operation, show channel number of SDO upper 4 bits

    5. (CS High to LOW)  0010 0000 0000 0000 // Enter into Auto1 mode

    Please share what happens with these commands, and scope shots

    Regards, Cynthia