Module type PLC including CPU module, I/O modules, memory,the power modules, bottom or a frame, these modules can be according to certain rules combination configuration.

In the user view,a detailed analysis of the CPU's internal unnecessary, but working mechanism of every part of the circuit.The CPU control works,by it reads CPU instruction, interprets the instruction and executes instructions. But the pace of work by shock signal control.

Unit work under the controller command used in a digital or logic operations.In computing and storage register of computation result,it is also among the controller command and work. CPU speed and memory capacity is the important parameters fot PLC.its determines the PLC speed of work, IO PLC number and software capacity,so limits to control size.

Central Processing Unit (CPU)is the brain of a PLC controller.CPU itself is usually one of the microcontrollers.Aforetime these were 8-bit microcontrollers such as 8051, and now these are16-and 32-bit microcontrollers.Unspoken rule is that you’ll find mostly Hitachi and Fujicu microcontrollers in PLC controllers by Japanese makers, Siemens in European controllers, and Motorola microcontrollers in American ones. CPU also takes care of communication,interconnectedness among other parts of PLC controllers,program execution, memory operation, overseeing input and setting up of an output.

System memory (today mostly implemented in FLASH technology) is used by a PLC for a process control system. Aside form. this operating system it also contains a user program translated foram ladder diagram to a binary form. FLASH memory contents can be changed only in case where user program is being changed. PLC controllers were used earlier instead of PLASH memory and have had EPROM memory instead of FLASH memory which had to be erased with UV lamp and programmed on programmers.With the use of FLASH technology this process was greatly shortened. Reprogramming a program memory is done through a serial cable in a program for application development.

User memory is divided into blocks having special functions. Some parts of a memory are used for storing input and output status.The real