A low level, microprocessor based direct digital system controller includes power supply means for providing a source of regulated electrical power to the controller. A field programmable processor means transfers selected data base information to and receives status signals from a field interface means, digitally executes control and energy management algorithms respecting those signals in accordance with computer program routines selected from a library of mnemonically identified routines residing in the read only memory (ROM) portion of the processor means. The processor means responsively directs programmed data and digital command signals to the field interface means which periodically updates the data base of the processor means, analyzes and conditions signals received therein from the processor means and from remote data points and selectively controls the data points. An operator panel means having information display means is coupled to the processor means for displaying and adjusting selected system operating functions. An optional field termination board facilitates connection of external wiring to the controller.