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I have a RasPi B+ running Raspbian and have connected an LED to GPIO 16 (pin 36) and another LED to GPIO 12 (pin 32).

It is my understanding that the GPIO ports are all off (low) by default and return to that state after a power reset. So, as expected, the LED on GPIO 12 is off when the device boots and only comes on when I pragmatically control it.

The LED on GPIO 16, however, comes on immediately when the Pi is powered on and stays on. During shutdown (running sudo poweroff), the LED begins to blink, then turns off for a short period before turning back on once the system is halted.

I can change the state of the LED pragmatically as well, but it seems something on the Pi itself is using that pin -- but I can't tell what or for what purpose.

Can anyone explain why GPIO 16 appears to be on by default and what is using the pin, causing it to change state during shutdown?

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  • You may have accidentally shorted the pin, have you ran anything else off that pin? – Matthew Pitzer Feb 6 '15 at 21:27
  • The fact that the OP can change the state via a program tends to negate your suggestion @MatthewPitzer. – SlySven Dec 7 '15 at 15:50
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gpio16 was the activity LED on pre B+ boards.

The most likely explanation is you are running a firmware revision which precedes the B+.

Are you using an SD card from another Pi?

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  • I bought the Pi this week as part of a kit that included the microSD card (which came pre-loaded with NOOBS). Is there a way for me to check the firmware revision to determine if it's up to date? – John M. Wright Oct 26 '14 at 13:57
  • uname -a should show the current firmware revision. My (not bang up to date Pi) shows 3.12.29+ #714 PREEMPT. – joan Oct 26 '14 at 15:57
  • The Pi had firmware version 3.12.29, so I upgraded to 3.2.31, however, that didn't change the behavior. Also, the LED is on continuously during the boot sequence, while the on-board activity LED is blinking and/or off during parts of the boot sequence. – John M. Wright Oct 31 '14 at 3:12
  • uname -a is actually reporting details of: the Linux OS kernel version, build instance and machine and a few other things. Some may not actually call the kernel firmware - although that could be worthy of a question in its own right! – SlySven Dec 7 '15 at 15:44

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