I have an Arduino Uno running a touchscreen shield (4Display), and a second Uno running a motor control shield (Adafruit). Both use i2c to control their respective shields.
I want the Uno with the touchscreen to send commands to the Uno with the motor shield, but how to do this isn't immediately obvious to me. I would use i2c, but since they're both i2c masters is there a way of getting one Uno to "listen" to the other?
There's always the less attractive solution of communicating through an assemblage of digital and analog IO ports, but a simple, clean, serial solution is more attractive.