Using digital pin 13 -- Problems??

Projects General Guidance
1

Due to a rather complex project, I will be using all of the available pins on my Arduino Leonardo, and have some questions on using digital pin 13.

I will be using digital pins 9, 10, 11, 12, and 13 to connect a Pololu DRV 8825 stepper motor driver. All five of the pins will be configured as output pins with pinMode(pinX, OUTPUT);.

I have read that there are certain problems when using pin 13 as digital input. And similarly, if I remember correctly, digital pins 0 and 1 can't easily be used in a project involving serial communication because they become active when serial communication occurs.

I have tested my code to run the motor driver and while I've not experienced any problems in using pin 13, I wonder if there might be some issues that could affect the driving of the motor attached to the Pololu.

So, here are my questions:

Does using pin 13 as digital output present any special issues that I should be aware of?

Is a default signal ever passed to pin 13? For instance when the Arduino is connected to a USB port, is pin 13 brought high or low?

Right now, pin 13 is connected to one of the three pins that controls microstepping on the Pololu DRV 8825. As such, I have some flexibility on how the pin is used. I could write the pin permanently high or write it permanently low. To minimize any potential problems in using pin 13, would it be better to bring the pin high or bring it low?

Is there anything else I could do in code that would reduce the likelihood of problems?

For what it's worth, I have checked the voltage drawn by the Pololu and it is negligible. So, there probably won't be a problem in terms of the onboard LED (connected to pin 13) limiting power to the motor driver.

2

Does using pin 13 as digital output present any special issues that I should be aware of?

Is a default signal ever passed to pin 13?

Connect an LED (with appropriate resistor) to the pin. Restart the Arduino. See for yourself what the LED does.

3

If you look at the Leonardo schematic on the Products page, you will see that D13 also connects to the input of an LMV358

which then drives the L LED.
The input current for the LMV358 is 11nA typical, 0.011uA. 1/100th of the 1uA max of the Atmega input current. I don't think you offboard source will have an issue.

D13 on the Uno is the SPI SCK signal, if you had SPI.begin(); called out in setup, you would then have an issue.

4

PaulS:
Connect an LED (with appropriate resistor) to the pin. Restart the Arduino. See for yourself what the LED does.

With my motor driving sketch loaded onto the Arduino, the on board LED doesn't light at all, which is logical as I brought that pin low in the void setup() routine. So that for the most part answers my own question!

CrossRoads:
The input current for the LMV358 is 11nA typical, 0.011uA. 1/100th of the 1uA max of the Atmega input current. I don't think you offboard source will have an issue.

Crossroads, I was worried that there might be something hardwired. As I will be permanently bringing pin 13 LOW in my sketch, this amounts to 'turning off' the on board LED. So would that in turn mean that the LMV358 wasn't getting any current anyway?

5

Arduino output has 2 output transisors (basically) - one to connect the pin to +5, one to connect to Gnd. If you are digitalWriting the pin Low, the Gnd transistor is turned on, and the part will try to sink any current on the pin to Gnd. Above 20mA, the voltage may start rising above Vds of the transistor, and above 40mA the transistor may fail.
Complex answer to a simple question, I know. Current goes, or current goes out. If both transistors are off, the pin is floating, which is the only time there is really no current flow - the LM358 input floats then also, and folks have reported the L LED to appear to be on, dimly.