4101 is a "programmable" controller that controls the sequence of machine actions. With the support of a fixed system program, it works in a cyclic manner following the steps of "input sampling -+user program operation -+output refresh", repeatedly executing user programs to achieve predetermined control functions, and supporting the use of "(virtual) relay language" (such as "ladder diagram") to write user programs. 4101 consists of a central processing unit (CPU), memory, input output interface, and programmer. The respective functions are as follows: The 4101 central processing unit (CPU) is the core, which accepts input programs and stores them. Scan the input status on site, execute user programs, and self diagnose. Memory is used to store programs and data. The 4101 input interface collects the signal states of various switch contacts on site and converts them into standard logic levels. The output interface is used to output electrical signals to control the object. The 4101 programmer is used for programming, editing, debugging, checking, and monitoring user programs. It can also display various statuses of the PLC.