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DRA744: OMAP5432, Can internal pull cells be applied when MUXMODE=SAFE?

David Smalley
Expert 7210 points

Part Number: DRA744

I would like to verify that when MUXMODE  is selected as "SAFE"=111b, that internal pull resistors are still applied when PULLUDENABLE is set.  The TRM says that SAFEMODE is a input with no function mapped to it so I expect so.  I need to ensure a high impedance on the pin with a pull down for EMI resistance.  So is SAFE mode with pull cell enabled preferable to some other input with pull cell enabled?

from TRM

Safe mode (mode 7) avoids any risk of electrical contention by configuring the pad as an input with no

functional interface mapped to it. Safe mode is used mainly as the default mode for all pads containing no

mandatory interface at the release of POR.

  • 0
    TI__Expert 7210 points
    Follow-on question - Do you have to also set INPUTENABLE when using MUXMODE=SAFE or does selecting SAFE mode put the buffer into input mode automatically?
  • 0 in reply to David Smalley
    TI__Mastermind 25170 points
    HI David,
    The pullup/down selection after power up is described in DM. And yes, I think that selection can be done independently of the muxmode. If you switch back to Muxmode=safe during run time, this will not set any pulls automatically, but you can continue controlling them in SW.
    Muxmode=safe will however disable the output buffer.
    Take into account that the INPUTENABLE bit is somewhat confusing. It will not switch the input buffer on and disable the output buffer! The only thing it does is to disable the Input buffer for power savings when it is not needed. I.e. the input buffer can be enabled/disabled independently of the output buffer. While the input buffer on/off is controlled by software, the output buffer on/off is controlled by the module using it.
    I can try on the EVM if muxmode bits switch also input buffer and pull selection bits to make sure I'm not wrong.
  • 0 in reply to Stanislav Stilyanov
    TI__Genius 14190 points

    David,

    Here is also an excerpt from the "optimization features" logic of the Pad Configuration Tool  that conforms to Stan's suggestion.  

    Thanks,

    Alex

  • 0 in reply to Alex Bashkov
    TI__Expert 7210 points
    Interesting! The diagram above implies that setting SAFE mode will activate the input buffer automatically because it recommends to DISABLE the input and activate the PULL when using SAFE mode.

    As Stanislav mentioned above, the output buffer is controlled by the selected function. In safe mode, it should not turn on the output buffer but if this is correct, it does turn on the input buffer even it INPUTENABLE is not set by SW? And presumably the Pull cells will be as set by SW.

    Can someone check how the design is implemented to be sure. I am specifically concerned with OMAP5 which is slightly different than J6 ( I had to select DRA74x to post because OMAP5432 is not mapped to a forum).
  • 0 in reply to David Smalley
    TI__Mastermind 25170 points
    Hi David,
    I don't think the diagram tells us if muxmode=safe enables the input buffer or not. If I'm not wrong, the software check is in place because the previous INPUTENABLE status is simply not known.
    I can check on a OMAP5 board whether muxmode bits alter inputenable, but I'm almost sure it does not.
    Regards,
    Stan