Controller hardware
The controller is based around a PIC16F84A. It has 13 I/O's, a timer, and not a lot else. To program it I'm using JDM programmer hardware, ICProg software, and the excellent Microchip MPLAB suite to compile and simulate the software.
H-bridge controller schematic
The controller board, attached to the main control board: Note the I2C cable running between them, which provides the main control board with power.
There's not much to the hardware. The address select pins need to be tied high or low depending on the I2C address that you would like the chip to use. The LED can be left out if you like. The crystal is 10MHz by default, but it can be adjusted to pretty much whatever you like given the caveats described elsewhere.
I use a 4-pin header to provide +5V, I2C data, I2C clock and ground. The plan is that each module on the robot will have two of these headers. They connect to the same pins so that modules can be daisy-chained together on the same bus. Each module can take its power from the bus, which simplifies everything greatly. Only one board needs to provide power to the bus. I'm doing it on the motor control board because it already has a (relatively) high voltage supply to run the motors.