Siemens ET 200S Manual page 26

Product Overview
1.1 What Are Distributed I/O Systems?
Distributed I/O Systems – Area of Application
When a system is set up, the inputs and outputs from and to the process are often
located centrally in the programmable logic controller.
If there are inputs and outputs at considerable distances from the programmable
logic controller, there may be long runs of cabling which are not immediately
comprehensible, and electromagnetic interference may impair reliability.
Distributed I/O systems are the ideal solution in such cases:
S The controller CPU is located centrally.
S The I/O systems (inputs and outputs) operate locally on a distributed basis.
S The high-performance PROFIBUS-DP bus system with its high data
transmission rates ensures that the PLC's CPU and the I/O systems
communicate smoothly.
What Is PROFIBUS-DP?
PROFIBUS-DP is an open bus system based on the IEC 61784-1:2002 Ed1
CP 3/1 standard with the "DP" transmission protocol (DP stands for distributed I/O
in German).
Physically, PROFIBUS-DP is either an electrical network based on a shielded
two-wire line or an optical network based on a fiber-optic cable.
The "DP" transmission protocol allows a rapid, cyclic exchange of data between
the controller CPU and the distributed I/O systems.
What Are DP Masters and DP Slaves?
The DP master links the controller CPU with the distributed I/O systems. The DP
master exchanges data by means of PROFIBUS-DP with the distributed I/O
systems and monitors the PROFIBUS-DP bus system.
The distributed I/O systems (= DP slaves) prepare the data of the sensors and
actuators locally so that they can be transmitted by PROFIBUS-DP to the PLC's
CPU.
1-2
Distributed I/O System ET 200S
EWA 4NEB 780 6024-02 07