The programs themselves are scanned / evaluatedĪs for the rung branches the program evaluates the top left to bottom right. The program processor updated the module I/O table and the module reads and from and wrights to the remote devices as it can. The remote I/O as its own module and processor with its own I/O data table that updated from the module. At the end of program 2 the processor updates the outputs from the output table then it checks the communication ports and handles them as needed.
Program 2 may call other programs from within it using jump sub function when the called program has ended the program execution will continue on the next rung below the jump. They update the Input data table from the real inputs, then the program 2. With the older processors they scan the base program (2) is always scanned and by default top left to bottom right. This is my understanding from information from Rockwell The older SLC and PLC’s scan differently than the newer Logix processors That’s a simple question but the answer is not quite as simple but it is important to understand it.
