Microcontroller – Is It Safe to Set Unused I/O Pins of ATmega8A to Input and Ground Them?


I'm still new to microcontroller, I don't know if this is already have a document about it.

I'm using the ATmega8A for my project and I only need 12 out of 23 I/O pins of the microcontroller, which mean that there are 11 pins that are unused. Since floating pin is bad, is it ok to set those unused I/O pins of the ATmega8A to input and connect all of them directly to ground. Also, I'll disable the all the internal pull-up resistor of the microcontroller since I'm using it for extreme low power application and those as I measure can draw up to 500uA.

I would like to know if it possible to connect all of them directly to ground. Will it cause any damage to the microcontroller like for example, there will be high current flow to the ground when start up. I'm using the 32.768kHz real time clock with 3.3V supply voltage for the ATmega8A.

Best Answer

Your solution will work. There are other options too, as wiring them directly to ground will prevent the use of those pins easily in case you need more pins for temporary testing and debugging.

Another solution is to not connect them at all, and then set them as outputs that can be high or low. If they have a PCB track and test pad they can be used as extra outputs for testing and debugging with an oscilloscope or logic analyzer.

It also allows the pins to be inputs with weak pull-up, so they can also be used as extra inputs for testing and debugging.

Of course if you really need to disable pull-ups for smaller power consumption then if you use these as debug/test inputs they must be fed with proper logic levels, or the pull-ups must be temporarily enabled.