If you are working at a company you then talk to the mechanical designer and make sure that all the motors, valves, limit switches, and sensors that you need are included in his design and are installed where they need to be according to the essay you wrote. It includes a list of all machine states altered by the code, It includes a list of all input and output variables, It includes requirements for data storage in the PLC memory. This includes the machine startup, run, and shutdown operations On the first day you write an essay to yourself describing what the block of code is supposed to do. The PLC needs to park the machine in a specified configuration before shutting off the power. There is a similar problem when shutting the machine off. When the PLC is turned on the program initialization step needs to determine what all of these states are before it can start running the machine. That could be valve or carriage positions, parts count, process duration, weights ,temperatures, speeds, and interlock status. The machine that you want to control is described in terms of states. One of the major mistakes that non programers make when programing the PLC is not understanding the importance of initialization of the PLC data base at startup. This includes the bit manipulation commands, the timers, the triggers, the counters, memory management and the specialized forms of looping and branching. Once you understand the basics of programing you will find that a quick look in the PLC documentation will provide all the details you need to use the specialized functions. The training is sufficient if you are modifying or debugging existing code. The classes do not teach one how to program. The company sponsored classes on PLC programing concentrate on explaining the trivia associated with the specialized PLC functions. The topics will include the main program, subroutines, the data base, program entry points, fixed point arithmetic, looping, conditional branching, debugging, and reusable code. The key concept is that the rules of programing apply to all languages. At the end of the class you will have a understanding of how a program is structured. Take a one semester class in C or Fortran programing.
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