• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 28 subscribers
  • Views 855 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Unused GPIO pins on an enabled port

Eric Anderson
Prodigy 10 points
Other Parts Discussed in Thread: TM4C1230H6PM

I have a question on a design using the TM4C1230H6PM processor.  Page 1054 of the processor data sheet is clear that all unused GPIO pins should be grounded.  However reading the Tiva design guidelines the picture becomes less clear when I read the highlighted sentence of the below paragraph.

Manual: http://www.ti.com/lit/ds/symlink/tm4c1230h6pm.pdf

Tiva Design Guidelines: http://www.ti.com/lit/an/spma059/spma059.pdf

3.10.7 Unused Pins
The preferred connection for an unused microcontroller pin depends on the pin function. Each Tiva™ C
Series microcontroller data sheet has a table in the Signals Tables chapter that lists the fixed function pins
as well as both the acceptable practice and the preferred practice for reduced power consumption and
improved electromagnetic compatibility (EMC) characteristics. If a module is not used in a system, and its
inputs are grounded, it is important that the clock to the module is never enabled by setting the
corresponding bit in the RCGCx register.

 

For example if I'm using PB4 & PB5 as GPIO, should I ground the rest of the pins on the port B GPIO module or leave them floating?  The unused pins aren't being enabled in code, but the module is being used.

  • 0
    Guru 47900 points

    Much like your, "attention to detail" in that vendor manual, "catch."

    My group's been at this for some time - believe you can never be: too thin, have enough money, or sufficient gpio!  So while you don't directly state - I sense that you may "bury" your (presently) unused gpio.  (i.e. fail to bring them to a board edge header - for (future) harvest!)  Cannot tell you number of times - such practice has saved us time/cost/effort of a board re-spin...

    Advice to "ground" such pins borders upon, "Alarmist" - and surely limits (eliminates) their future use.  (writer sounds like the guy next to me on recent flight - that guy only one wearing hospital mask...)  Dawns that such "sound" advice forces users to, "Buy more MCUs when even 1 or 2 "unused gpios" become needed - as they surely will!  (caveat - if yours is a 10K+ build - cast in stone - my guidance here dilutes (slightly))

    To your specifics - believe an acceptable practice (this vendor's ARMs & others) is to set unused pins as gpio inputs with weak pull-down resistors.  As this is a software setting - you may later alter it - but we've found this to be reasonable - and in no way does this "disable" these pins for future use.  Should your boards be destined for a high ESD environment - cannot hurt to force a 100 ohm R in series w/each such (unused) pin - too. (i.e. between MCU pin & board header)