SCAN is the procedure, which any sequential operation of the program controller must go through. It is the process of the operation going from the top to the bottom of the ladder in the ladder diagram. The process results in all updated outputs, which correspond to the given inputs. The process of SCAN takes place from the left to the right of each rung in the ladder diagram. Scan time is basically the total time needed to read the input, process the logic of the program and update the corresponding output in a single cycle. Generally, the time for SCAN is of the order milliseconds and it is a continuously running process.