According to the function PLC has three main functions. They are processing (to execute program logic instruction), Memory (to store the processing result), and Input / Output (to receive data from outside and transmit the processing result).
Internal architecture of PLC consists of CPU that is containing a microprocessors system, memory, and a series of input / output. CPU controls and carries out all operations in the PLC. Counterfeit devices connected to a clock with a frequency between 1 to 8 MHz. This frequency determines the operating speed of the PLC and provides timing and synchronization mechanisms for all elements in the system.
The information in the PLC is transmitted by a digital signal. Internal channels which is through by digital signals called as Buss. Physically, a bus is just a passable conductor that is passable by electrical signals. This conductor could be a path on printed circuit board (PCB) or the wires in the cable.
CPU uses the data bus to send data to the PLC elements. The address bus is to send address of data storage locations. And bus control is for signals associated with internal control processes. The bus system is used for communication between the ports input / output with the unit input / output.