Abstract: A machine control system includes a CRT on which a five bit screen image code is displayed, indicative of the particular screen image being displayed. Five sensors are mounted such that each senses a respective one of the code regions of the screen image code and generates a respective sensor signal. A controller compares the sensor signals with the screen image code for a commanded one of the screen images and indicates any disparity therebetween. In this way, a positive check is provided that the display screen actually displays the intended one of the image screens, and that the screen is in fact functional. In addition, a plurality of pushbuttons are provided which operate in two separate modes. In the first mode the pushbuttons provide programming inputs to the controller and in the second mode the pushbuttons act to control the machine directly via an alternate device, bypassing the controller.