A programmable controller includes at least one user input interface, and an input register, at least one user output interface, programmable logic hardware and program loading means.The user input interface and input register is for connection to process plant and/or machinery to provide sampled and stored input data in digital form. The user output interface is for connection to process plant and/or machinery and receives output data in digital form. The programmable logic hardware includes a plurality of basic logic elements and electrically configurable interconnections. The interconnections are configurable to interconnect the logic elements as a user control program circuit and to connect the user control program circuit to the input and output interfaces. The program loading means enables the user to configure the programmable logic hardware as a circuit implementing a user control program prior to initiating control of the associated process plant and/or machinery.