Abstract: A digital input circuit is provided wherein previous digital data is stored in a holding register. Subsequent data is compared with the data in the holding register to determine whether or not a change had occurred in the input data from the primary sensors. If no change is detected, the system effectively "passes" on that scan of the data. If, on the other hand, a change has been detected an interrupt signal is generated for transmission back to the host computer. The host computer may then initiate a "read" sequence. The "read" sequence under ordinary circumstances, includes updating the data in the storage register before enabling the outputting of the digital data.

Abstract: An analog output control circuit provides an arrangement whereby digital data from the control computer is supplied simultaneously to a number of output boards along with address data for selecting a particular one of the several boards. Logic control means is provided for responding to an address code for enabling the selected board. Additional control logic is provided for responding to control signals from the computer for selecting a particular one of the several output units included on the output circuit board. Control logic is also provided to prevent the output units from being changed in the absence of logic control or power supply.