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ADC7951 mode programming

Steve April
Prodigy 100 points
Other Parts Discussed in Thread: ADS7951

Hello - 

I am connecting the ADS7951 to an FPGA which will continuously read frames in auto-2 mode.  I am not clear on how to change the ADC mode from manual (power-up default) to auto-2 and just have the ADC auto sequence through all channels as I read them out with the FPGA.

The spec,  SBAS652A –MAY 2014–REVISED AUGUST 2014, Figure 54, reads as if I need to continually program frame n+1 as I read data out but then on the very next page it suggests that, once in auto-2 mode, I can run in continued operation mode, and I assume I do not have to keep writing programming frames.  

For example, all I want to do is run the device in auto-2 mode and use all channels.  When the chip powers up, can I not I just program the ADC to put it into auto-2 mode and then continuously read data out,  or do I need to write two frames, one to put the chip in auto-2 mode and then another to put the ADC in continued operation mode?   ...Or do I need to continually write programming frames as figure 54 suggest?

Thanks in advance for your help

Steve

 

  • 0
    TI__Expert 8955 points
    Hello Steve,

    My understanding of your requirement i as follows.
    You need to capture all channel with auto increment starting from Ch0.
    During this capture, the range settings will not change for each channel.

    To get into the Auto-2 mode you need to program first 3 frames with SDI contents as described in Table 5. At the end of 3rd frame, you would have entered Auto-2 mode.

    From 4th frame onwards you need not send any data on SDI (continued operation mode). SDI should be low in the entire frame. Device will auto increment channel with each frame.

    Thanks & Regards,
    Shridhar.
  • 0 in reply to Shridhar%20More
    Prodigy 100 points

    Hi Shridhar,

    The method you described to get the ADC into Auto-2 mode works however we have also found that we only need to program one frame followed by holding SDI low, to get it into that same continuous mode using all available channels.  Is there a specific reason for three frames?  

    Thanks!