Date Added: Aug 2012
Designing of microprocessor based controllers requires specific hardware as well as software programming. Programming depends upon type of the software whether operating software or application software. Programming requires knowledge of system configuration and controller specific programming. Programs are always in digital form so microprocessor can control directly at digital level called Direct Digital Control (DDC). In the early 1960 computer based controllers were used. They were having one main frame computer and all control action was dependent on it, moreover they were costly. But with the advent of microprocessor cost of controlling the plant decreased very less.