From the sub-structure, PLC is divided into fixed and modular two. Fixed PLC including CPU boards, I / O board, display panel, memory blocks, power and so on, into a combination of these elements are not removable as a whole. Modular PLC including the CPU module, I / O modules, memory, power supply modules, backplane, or chassis, the modules can be configured according to certain rules of combination.
In the user view, a detailed analysis of unnecessary CPU's internal circuitry, but the working mechanism of the various parts of or should have sufficient understanding. CPU control of the CPU controller, from which to read instructions, explanation of command and execution. However, the pace of work from the vibration signal control. Computing devices used in digital or logic operations, under the command of the work in the controller. Register to participate in operations, and store intermediate results of operations, it is under the command of the work in the controller. CPU speed and memory capacity is an important parameter PLC, which determines the rate of PLC work, IO number and software capacity, thereby limiting the size of the control.
