The Mitsubishi A2SCPU CPU unit is a programmable logic controller (PLC) module with a program memory capacity of 14K steps. It supports up to 512 input/output (I/O) points, making it suitable for medium-scale automation systems. The operational cycle of this PLC follows a sequential scan process, which consists of three essential stages: input sampling, program execution, and output refresh.

During the input sampling stage, the PLC first scans all input terminals in a sequential manner, reading the ON/OFF status or data values stored in the input latch circuits. This information is then written into the corresponding input status registers, effectively refreshing the input data. Once this process is complete, the input ports are immediately closed, and the PLC proceeds to the next stage—program execution. This design ensures that the input data remains stable throughout the program execution phase, preventing any changes in external signals from affecting the logic processing.