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ADS1282 SPI interface Problems.

Chris Snell
Prodigy 30 points
Other Parts Discussed in Thread: ADS1282

I've got a similar problem, where I can't recover from a SPI bus lock up.

I have a similar set up where the SPI bus is multiplexed to 3x ADS1282 via a CPLD.

If the microcontroller driving the SPI bus resets, the ADS1282 locks up and stops toggling the DRDY pin.

I have a hard pull-up on the ADS1282 RESET pin so am unable to toggle it without a hardware change.

When the ADS1282 locks up I can only get it to work again by cycling power to the board.

The data sheet suggests that I should be able to recover from a lock up by holding the SCLK low for 64 DRDY cycles.

I've tried holding the SCLK low for >300ms and and have checked that this period is clean and there are no glitches.

I then send a reset command, and try to read from the device, the device remains unresponsive, no DRDY and no data.

Is this a known issue?  Do I need to modify my hardware so that I can toggle the RESET pin, or is  there something else I can do to recover from the lock up?

Regards

Chris 

  • TI__Guru**** 182421 points

    Hi Chris,

    Welcome to the e2e forum!  I'm sorry to hear that you are also experiencing SPI lockout issues with the ADS1282.  Can you please send along some screen shots of your communications interface (the SCLK, SDI, SDO, etc)?  Do you have any idea why your micro might reset?  If there is some sort of voltage brownout/droop that causes your CPU to reset, that might also cause problems with the ADS1282 and may explain why the SCLK reset is not working.  Using the HW reset pin may help, but it might not get to the root cause of your issue.

  • in reply to Tom Hendrick
    Prodigy 30 points

    Hi Tom,

    We are deliberately resetting the microcontroller as part of our fault recovery testing.  The power supplies to the ADCs are stable throughout the reset.  The reset could occur at any time, including during an SPI transfer.  It is also probably that the CLK input is unstable and interrupted during the reset.

    When the microcontroller boots up, it holds the SCLK line low for 300ms in order to reset the SPI bus.  It then sends a SDATAC and a RESET command via the SPI bus.  The configuration registers are updated.  When reading from the device, all registers read as zero. A RDATAC command is sent, but we do not get a DRDY signal.

    I have modified one of our boards to allow the reset pin to be toggled; this does solve the problem, but is a very difficult and expensive solution as we have chosen to tie the reset pin high in our board layout.

    I had assumed that once the SPI bus was freed, sending a RESET command would have the same effect as toggling the reset pin.  Is this not the case?

    The same code is used during a cold reset and the ADCs function properly.

    I hope this gives you the information need to help debug the lock up issue.

    Regards

    Chris

  • in reply to Chris Snell
    TI__Guru**** 182421 points

    Hi Chris,

    There is nothing that I am aware of that would cause this to happen - sending the reset command should clear/reset the part.  Are you toggling the /CS line as well?  Can you send screen captures that might help us try to reproduce your setup??  

  • in reply to Tom Hendrick
    Prodigy 30 points

    The ADS 1282 does not have a /CS pin.

    Either holding SCK low does not fully reset the SPI bus, or, sending the RESET command does not reset the part in the same way as toggling the reset pin.

  • in reply to Chris Snell
    TI__Guru**** 182421 points

    Sorry Chris,

    My bad on the /CS comment - can you send along screen captures of the control lines to the ADS1282 so that we can try to reproduce the same conditions you have?

  • in reply to Chris Snell
    TI__Guru**** 182421 points

    Hi Chris,

    Have you made any progress here?  Are you able to send the screen shots i asked for?