I/O Modules
The status of input devices, which is in form of analog, is affected to the module of input. This part of PLC converts the status of analog into form of digital and transfers to the CPU through bus. After processing the data of CPU produces the status of O/P which comes in a module of O/P where it acquires converted into the form of analog and subsequently transfers to the devices of O/P.
CPU
CPU is an element of control. It is essentially separated into the memory area and processor area.
Processor
It processes the data by performing the instructions saved in memory and generates related the data of O/P.
Memory
It is store where the programs are saved. The memory is in general separated into two parts program memory and data memory.
Organization of Memory
The CPU comprises of the memory, where data and programs are stored and the processor processes the data and performs the program. In the majority of the memory of PLC is separated into particular areas. The mainly common areas are Data area and Program area. In some PLCs these parts are of permanent size. While in the some of PLCs like Allen Bradley, the size of these parts are not permanent, but rely on the requirements of program.
Program Area
This part is where the user goes into all the programs, which will be checked constantly when the PLC is in operating mode. The program make a decisions how the outputs of the PLC will perform. In general the majority of the PLCs use the ladder logic for programming. All these PLCs have software integrated which transfer the logic into a code, which is after that utilized by the processor of the CPU to produce an output.
Data Area
The data part in a characteristic PLC is separated into a number of tables also recognized as Data Files or data Tables. A characteristic PLC will have diverse data files for different types of data, the majority regular being data of Input, data of output, data of bit (also submitted to as the internal contacts or internal relays), integer data, timers, and counters. The data files include the status of information related with the external I/O and all the other instructions that you utilize in the main 6 and subroutine files of ladder program. Additionally, these files save information with reference to the processor operation.