An improvement in the operation of an electric power plant utilizing a steam turbine controlled, in an automatic mode, by means of a digital computer, is accomplished by simplifying the interaction between the programmed automatic process control and the manual backup control. The position setpoint for each of a plurality of valves in the system to be controlled is established as a direct digital holding function in a respective bistable relay register. In addition, a single valve control holding register is provided which is coupled to all of the valve position controls in parallel. Automatic operation is then possible in either single valve or programmed sequential valve modes, and the programmed interaction to accomplish switching from manual to automatic control is simplified by updating the automatic control status until the single valve holding register has a setting equal to the manual control representation before consummating the manual to automatic switching. The direct digital holding registers also improve total system operation in eliminating drift with respect to the valve positions represented so as to extend the period of reliable operation in the manual mode, and also make it possible to retain the last valid position setpoints held in the respective registers prior to a computer power failure.