Abstract: In a data processing system having a plurality of units and a priority controller for controlling access to a bus by any of the units, each of the units is provided with a lock register having a stage corresponding to each unit connected to the bus. Each word placed on the bus by a source unit includes a lock bit which, in each unit except the source and destination units, sets the stages of the lock registers corresponding to the source and destination units. When a stage of a lock register is set it prevents the unit in which the register is located from attempting to communicate with a unit whose stage of the lock registers is set. On the last transmission between two units the word placed on the bus has a false lock bit which resets the stages of all of the lock registers corresponding to the source and destination units.

Abstract: Apparatus for controlling the advancement of punch cards or like sheet material past a plurality of work stations such as may comprise a data recorder used in the preparation and processing of punch cards. Control means are provided to sense the nature of an operation being performed on a particular card as well as the presence of punch cards at other of the plural work stations comprising the system and in response thereto selectively energize the advancement mechanism such that each punch card processed through the system will be advanced at an optimum rate. In the event no punching or printing operation is to take place on the punch card the speed of the advancement mechanism is increased considerably in excess of that which would otherwise enable the advancement mechanism to be accurately stopped.