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ADS8638: Have not found correct setup to get Auto-scan mode operating

Tom Lee10
Prodigy 10 points
Part Number: ADS8638

Following the flowchart on page 63 (Figure 93) I have successfully, manually configured the ADS8638 on a custom board to read any of the 8 channels.  For my design, an FPGA module will be reading data from channels the micro wants to monitor.  As such, I am counting on using the auto-scan mode. 

With my custom board:

  1. The Auto-Md Ch-Sel selection register (Page 0, Adress 0x0C) can be set and read to enable any (all) of the channels. 
  2. The channel range registers (page 0, address 0x10 to 0x13) can be set and read. 
  3. Set Auto mode operation by writing 0x00 (have tried resetting the sequence) to page 0, address 0x05.
  4. Successively write 0x0000 for continue operation to pull out sampled data.

The result is the data coming back is whatever the last manual accessed channel.  

Regards,

Tom Lee

  • 0
    TI__Mastermind 24970 points
    Hello Tom,

    To make sure I understand correctly, you have been able to confirm step 1 and 2 with read back from the device, is this correct? if so, this is good, this elimates any timing errors.
    In step three, it seems you are trying to go back and set the device to auto mode, after configurating the channel select andchannel range.
    Would you try selecting auto mode first, 0x05, then the channel select, followed by the channel range; so moving your step 3 to be the first.

    Also, would you pleae provide a scope shot of the digital communications, including: SDI, SDO, SCLK, and CS.

    Regards
    Cynthia
  • 0 in reply to Cynthia
    Prodigy 40 points

    Hello Cynthia,

    Correct, communication between the FPGA and ADS8638 is stable.  Writes and reads from register are good and manual reads from channels shows appropriate data.

    I have tried a number of different combinations (started off following the flowchart on page 63 of the data sheet), but will try a fresh power up and do step 3 before 1 & 2.

    I will need to add chipscope to my FPGA build for getting a trace of the SPI port.  I will post it once I have it.

    Regards,

    Tom

  • 0 in reply to Tom Lee81
    Prodigy 40 points

    Hello Cynthia,

    This morning I got free of higher priority things and got back to the ADS8638.  I built the FPGA load with the logic analyzer.  Started walking through the steps, collecting the logic analyzer screen shots and when I reached the step of writing to the auto-scan mode register, I realized that I had put the 0xA for the 0x5 address value in the wrong nibble.  I had it as 0xA000 where it should have been 0x0A00.  Once I fixed my gaff, and went through the rest of the setup, auto-scan works fine.

    Thank you for you time and efforts.

    Regards,

    Tom

  • 0 in reply to Tom Lee81
    TI__Mastermind 24970 points
    No problem Tom, glad everything worked out!
    -Cynthia