Use of priority based interrupts, to get the work done according to priority, is of prime important, in automation. First develop the logic, and the sequence of task to be carried out for your system to be built. Utilization of available component in best possible way, needs detailed study from manuals (processor, I/O, EPROM, ADC/DAC and buffers needed).Refer my research papers on,' Online instrumentation, loading, control and protection for transformer and electrical machines..........'. If your system is not too complicated, can used, any microcontroller available in market, would be eazier and cheaper.