Milton Bradley Plus One has an 8-pin DIP marked with National Semi's logo and /029 MM 57405N. 2 pins are power and ground, 4 are inputs from the orientation sensor, one is an output to a piezo, and one is connected to a resistor to power and a cap to ground, so oscillator? I'm not sure if this is a microcontroller in a smaller package, or an ASIC like Simon.