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L-137: Pin Multiplexing - unused peripheral signals always available as GPIOs?

wsw
Intellectual 295 points

Hi,

when I use eg. EMIF A for NAND-Flash or MMC/SD card, I don't need all signals of the peripheral, can I use them as GPIOs then (eg. the EMIFA address lines)?

The user's guide of the McASP states so (2.3.6), but in most of the other peripheral UGs there is no specific info referring to unused signals/pins.

What makes me suspicious is this passus from the L137 datasheet: "Note that the input from each pin is always routed to all of the peripherals that share the pin; the PINMUX registers have no effect on input from a pin."
So: could it happen that an unused pin (e.g. wait or enable signals) of an activated peripheral which is configured as GPIO interfers with the function of the peripheral?

Stefan

  • 0
    TI__Guru*** 125430 points

    Yes, you can configure the EMIF address lines as GPIO.  As long as you're using an EMIF mode where the address lines aren't used (e.g. NAND) then it won't matter that the inputs signals are internally connected to the EMIF.  You should be more careful with control signals.

  • 0 in reply to Brad Griffis
    Intellectual 295 points

    Brad Griffis said:

    Yes, you can configure the EMIF address lines as GPIO.  As long as you're using an EMIF mode where the address lines aren't used (e.g. NAND) then it won't matter that the inputs signals are internally connected to the EMIF.

    Good. I guess/hope this is true for other peripherals too?

      You should be more careful with control signals.

    Why? Because I could need them or because they could be interpreted by the peripheral in a way I wouldn't expect when using as GPIO (see citation in the first posting)?

    Thanks,
    Stefan

  • 0 in reply to wsw
    TI__Guru*** 125430 points

    wsw said:

    Yes, you can configure the EMIF address lines as GPIO.  As long as you're using an EMIF mode where the address lines aren't used (e.g. NAND) then it won't matter that the inputs signals are internally connected to the EMIF.

    Good. I guess/hope this is true for other peripherals too?

    [/quote]

    Yes, the multiplexing on OMAP-L13x is done on a pin by pin basis through the PINMUXn registers.  You have control over the functionality of each pin (well, each pin that is multiplexed with several functions which is most of them).

    wsw said:

      You should be more careful with control signals.

    Why? Because I could need them or because they could be interpreted by the peripheral in a way I wouldn't expect when using as GPIO (see citation in the first posting)?

    [/quote]

    Yes, exactly for that reason.  Generally that should not be an issue.  For example with the SPI you can configure it for 3-pin, 4-pin, or 5-pin operation.  If you decide to use the /ENABLE pin as GPIO just make sure you don't configure the SPI for a mode that would use that pin!

    Brad