Abstract: The method and device are used to control outputs to a plurality of output devices relative to inputs and for synchronizing the updating of selected outputs with the occurrence of an external event. An interrupt signal is derived from an external event at one or more input devices and supplied to a micro-computer. A user ladder program is provided in the device for controlling the outputs and one or more interrupt zones are provided in the ladder program and are immediately responsive to the interrupt signal for instantaneously updating selected outputs. Each interrupt zone includes enabling means, an opening boundary, addresses of inputs to be fetched, a body of instructions and a closing boundary.