# Why would a pin not go high on an Arduino?

I'm using a SparkFun-built Arduino Pro Mini 3.3V / 8MHz. One thing I need it to do is toggle the gate pin on a MOSFET, and that's not working for some reason. Getting in there with a multimeter, I see that the voltage on the pin never goes HIGH. The only thing I have running on there is the following bit of code:

void setup()  {
pinMode(A7, OUTPUT);
}

void loop() {
digitalWrite(A7, HIGH);
}


Any thoughts on either configuration or electronics that could be causing this?

The pertinent part of the schematic is:

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From the schematic, it appears that both A6 and A7 are used in a similar way. Does the A6 pin work if wired to the RUD_EN connection (and vice versa)? Do you have a replacement Arduino Mini to test with, the processor or board connection may be bad? – Ron J. Apr 7 '14 at 13:41
No, they're behaving the same way. I did test with another one - no go. It's definitely either a wiring issue or a code issue, not something with the board – kolosy Apr 7 '14 at 13:44

## 1 Answer

A6 and A7 are Analog Input Only. This is most likely what your are running into.

The TQFP package of the AtMega328 has 2 more inputs that the DIP package (A6 and A7), but they are analog input only. 1.1.9 in the datasheet.

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sigh yes - it's looking that way. – kolosy Apr 7 '14 at 13:44
@kolosy - If you could see fit to add a small I<sup>2</sup>C parallel port expander to your design your could take the two wire port of the MCU and get support for 8 I/O pins at the expense of only two on the MCU. At least the port expander could be used to drive RUD_EN and WINCH_EN and monitor RUD_V and WIN_V. – Michael Karas Apr 7 '14 at 14:39
I'll look into that, thanks. I think for the time being, I just need to move some things around, still have enough GPIOs. – kolosy Apr 7 '14 at 14:51