Abstract: The sheet-presenting unit presents received sheets to the printing instrumentality of the machine. The sheet-feeding unit feeds sheets to the sheet-presenting unit. The two units have activators which can be enabled and disenabled. The operator of the machine initiates a start signal. A sheet detector generates missing-sheet, skew-sheet and muliplee-sheet signals, indicating the condition of the sheet at the sheet-presenting unit. Enablement stages determine whether the activators for the feeding and presenting units are to be enabled or not. When the activators are enabled, the start signal is automatically extinguished. A logic circuit receives the start signal and the signals from the sheet detector. The logic circuit has pre-start-up and post-start-up modes of operation, corresponding to generation and termination of the start signal.