Yes, you can use a digital signal on the 3984 to control direction, disable, etc inputs. The digital signal must be from an open collector type device that is capable of sinking a 10mA minimum current and withstanding 12VDC. The 10mA is the minimum value for the open collector device, and is the typical current that is going to be used by the circuit. Anywhere up to between 30mA and 50mA on the open collector device is acceptable to use.