During each operating cycle, the processor reads all inputs, takes these values, and energizes or de-energizes the outputs according to the user program. This process is known as a scan. Because the inputs can change at any time, the PLC must carry on this process continuously.
1. I/O scan – records status data of input devices. Energizes output devices that have their associated status bits set to ON (1)
2. Program scan – instruction are executed sequentially.
