8051 and Curtis Motor Controller

Hi all. A group at my University is working on driving a golf cart with a microcontroller for a project. The golf cart has a Curtis PMC Model 1205 motor controller and we want to control it with an 8051 microcontroller. We're only concerned with making the unit go forwards. The Curtis manual has a test circuit for the motor controller that we have tested sucessfully but now we want to add the microcontroller to the test circuit. I have uploaded the original test circuit schematic to

I'm wondering where or how we could put the microcontroller in this circuit to test if the microcontroller can control the motor control circuit.

Thanks in advance, Blake