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Mode switching in the TLC5926

Daniel Hillstead
Prodigy 30 points
Other Parts Discussed in Thread: TLC5927, TLC5926

Attempted to ask this question via Technical Support but I haven't heard anything in a few days so I thought I'd try here.

Question about mode switching in the TLC5926. I am able to switch into the special mode and write to the configuration latch. However, when I use the same process to switch back to normal mode, it fails to do so unless I repeat the process a second time. There is a note in the documentation for this part that states "The signal sequence for the mode switching may be used frequently to ensure that the TLC5926/TLC5927 is in the proper mode." What does this mean? Is it expected that mode switching may fail and the signal sequence should be repeated? How many times should I attempt? Is there a way to know I have succeeded the mode switch?

  • 0
    TI__Genius 14890 points

    Daniel,

    The process to get into special mode was created to reduce the potential for inadvertently entering special mode.  It is possible that an application can set up a sequence that would do that so I expect the note was added as a way to reset if the user was not sure of the current mode.  Entering normal mode while in normal mode does not do anything but keep the device in normal mode.

    I do not know of a reason why 2 attempts would be required.  The simplest way to verify mode is to monitor the output response to changing data that is shifted in.  There is not a direct feedback method to signify mode.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 30 points

    Dick,

    Thanks for the response.  Your explanation of the note in the documentation makes sense.  I still don't know why it takes 2 attempts to switch from special mode to normal mode but at least I know that is not expected behavior.  I am able to verify the mode switch by monitoring the output response but that will not be sufficient once the product leaves my office.  I'll take another look at my code for mode switching and see if there is something I can do to fix it.  Can I infer that you have not seen this issue when switching back to normal mode?  And that your process for switching between modes is exactly the same except for the LE level?

    Thanks,

    Daniel

  • 0 in reply to Daniel Hillstead
    TI__Genius 14890 points

    Daniel,

    I have not spent a lot of time lately looking at switching modes.  I will try to set up in the lab and take a look to see about mode switching.  I do know that we had an engineering board that worked well.  I don't have access to the original code, but I don't believe it was a 2X attempt.  I have another board I can try as well.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 30 points

    Dick,

    I have found a solution that solves my problem.  I am shuting down the spi bus and manually pulsing the clock in order to perform mode switching.  Using Figure 12 from the TLC5926, TVL5927 specification, my mode switching algorithm only pulsed the clock 4 times before restarting spi clock.  This was sufficient for switching to special mode.  In order to swtich back into normal mode, the 5th clock pulse is required.  I have added the 5th clock pulse and everything is now switching correctly.  Thanks for your help.

    -Dan

  • 0 in reply to Daniel Hillstead
    TI__Genius 14890 points

    Dan,

    Great news!  Please continue to post if you have more questions.

    Regards,

    Dick