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Tham khảo tài liệu 'theory and design of cnc systems part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 232 7 Programmable Logic Control Output Unit and the output signal converter amplifies the output signal of the CPU to activate the external device. Further the output signal terminal is used for connecting the PLC system and external devices. In addition the Output Unit includes a circuit to prevent excessive current due to short circuits in the output signal terminal. The CPU Unit is the core module of the PLC system executing logic calculation and arithmetic calculation by interpreting the PLC program and the final results are sent to the Output Unit. In other words the CPU Unit handles the serial or parallel sequence logic operations e.g. AND OR and NOT timer or counter operations that are used for controlling the elapsed time based on an internal pulse counter the four arithmetical operations the comparison operation junction operations e.g. JUMP and CALL mathematical function operations e.g. COS SIN TAN and Square root data transmission and code conversion. Program Memory which stores the user programs and System Memory which stores system data OS and application S W can be rewritable and can keep the data using an internal battery even in the case of power failure. In addition auxiliary units such as the programming tool and interface units for RS-232C serial communication and ethernet communication are included in the PLC system. Therefore the maximum input output contact points the speed of the CPU Unit in FANUC this is defined as the time consumption per step the size of the Program Memory in FANUC this is defined as the maximum number of steps. the kinds of commands and the kinds of allowable external communications are specified to represent the performance of the PLC system. The method of executing the command specified in a program is as follows. A PLC programmer creates edits and saves the PLC program by utilizing a programming language such as the ladder diagram instruction list etc. After saving the PLC program the PLC system scans and executes the
