A programmable controller has a rack that houses and electrically connects a number of I/O modules and a processor module. The processor module includes a external communication network interface, a system memory, a processor section which executes a user-defined control program and a I/O interface that handles the exchange of data with the other modules. The I/O interface has circuitry for pre-processing data from defined input modules, thereby relieving the processing section of certain tasks. The shared memory contains information defining the input module from which to obtain data for pre-processing and the bits of that data to be examined for specified logic level transitions. The stored information also designates the frequency at which the data is to be read from the defined input module and how many occurrences of the specified logic level transitions must take place before the I/O interface signals the processor section that the pre-processing is complete.