Abstract: A computer based process control system includes a digital event counter input circuit wherein a number of data sources are scanned. A sensed status of the individual input point is compared with the previous status of that point to determine if a change of status has occurred, indicative of an event to be counted. The previous status is stored in a dedicated register. If the comparison indicates that a countable event has occurred, a counter is incremented; also the dedicated register is updated to indicate the present status of the scanned point. The counter status is stored in an accompanying memory which may then be read out by an external device such as a processor.