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MSP430F5438A: P5.3/X2OUT GPIO input characteristic

Ted Huh
Expert 3595 points

Part Number: MSP430F5438A

Hi,

My customer(500k/yr) asks the characteristic of the one open pin.

They left P5.3/XT2OUT pin open, and set the pin gpio input. they didn't set any other registers.

and when they read the BIT3 of P5IN register it always shows 1 until now.

1. Will P5IN.3 be always high with their hardware and software setting?

2. Could TI share internal block diagram / schematic with my customer? more detailed version than datasheet.

Best Regards,

Ted

  • 0
    Guru 74080 points
    A floating input is never a good idea. Better tie an unused input to DVcc or GND. Or configure it to be an output either being low or high.
  • 0 in reply to Dennis Eichmann
    TI__Expert 3595 points
    Yes you are right. However, they already started MP without noticing it, That's why they need a characteristic of P5.3
  • 0 in reply to Ted Huh
    TI__Guru**** 223987 points
    Hi Ted,

    TI recommends that when unused, the XT2OUT pin be left open and driven as a GPIO output. Since left as a floating input you can't expect it to remain in either a high or low state. There are no characteristics provided outside of Section 5.7-5.9 & 6.10.6-6.10.7 of the Datasheet.

    Regards,
    Ryan
  • 0 in reply to Ted Huh
    Guru 327860 points

    When in GPIO mode, P5.3 is not different from any other GPIO pin.

    You don't need a more detailed schematic; a CMOS input is always connected to the gates of an NMOS and a PMOS transistor. See figure 1 of Implications of Slow or Floating CMOS Inputs (SCBA004).

    The pin is floating. There is nothing that keeps it at any specific level; it happens to read high in that specific circuit, but that is probably not a proper high level but only something that happens to be higher than the threshold. You cannot rely on past oberservations; the smallest amount of noise can make the input go low. In any case, there will be cross-currents that might cause damage over time, and if the pin is floating near the threshold, switching currents can become much higher, and oscillations can result in excessive noise on the power lines that makes this chip or other chips fail.

    That floating pin must be removed, by changing either software or hardware.

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