 PLC's control processes by continually scanning the latter logic program. The scan of a PLC consists of three major steps. Step 1. Check input status. Step 2. Execute program. And Step 3. Update output status. During the check input status, the PLC determines the state of each input device in the system, and writes the values into the input image area. In the next step of the scan cycle, the PLC executes the program one instruction at a time. The values of the output table are changed based on the status of the inputs. In the last step of the scan, the outputs are energized or de-energized as defined in the output table. Here the three steps of the scan are completed. The scan cycle is repeated. The entire scan process is demonstrated further here. When the limit switch is activated, the input module detects a voltage and an on condition is updated in the input table with a value of one. During the execute program step, the PLC sets the input and output instructions on. The output status is updated with the light changing state from off to on as defined in the latter logic. The PLC scan follows a specific pattern to execute the program. The first pattern is referenced as horizontal scanning, where the program is examined from the first command left to right across the rung and top to bottom. Vertical scanning, on the other hand, examines the input and output instructions from the first command vertically column by column and left to right.