I have two Arduino Dues working in tandem for a project. One interprets the signals from a hand full of membrane keypads, and is connected to the other Due via several (9ish) digital pins. The two arduinos share a common ground. The second arduino has motion algorithms on it that operate a several degree of freedom machine (stepper motors).
When a kepyad is pressed, arduino #1 sets a digital pin to high, which is read by arduino #2, and a motor is jogged.
A problem I am encountering is that when I am uploading a sketch to arduino #1 (the one responsible for interpreting the keypads) it sets random pins to high. As a result, when I am uploading a sketch random motors start turning. As soon as the sketch is successfully uploaded the strange behavior stops.
Anyone have any idea what this could be?