Bus communication, Transmission systems

This catalog is out of date, see note on page 3

Bus communication

PROFIBUS-TM

■Overview

The AS 488/TM and AS 388/TM automation systems are connected to one another, to OS 525 or PCS7/TM-OS operator systems and to PCs/programming devices with the PROGRAF AS+/NT configuration software via the PROFIBUS-TM system bus.

The connection to PROFIBUS-TM is made:

•Using an EXM 478 extension module with IF 964 interface module for AS 488/TM systems and CS-L2 bridge

•Using an EXM 378-2 module with IF 964 interface module for AS 388/TM systems.

■Mode of operation

The PROFIBUS access procedure is similar to that of the CS 275 bus system, and operates according to the "Token passing" pro- cedure corresponding to EN 50 170 (PROFIBUS). Characteristic for PROFIBUS-TM is that the TELEPERM M communication mechanisms of the CS 275 bus system are used, e.g. AKS, BKS, MKS and PL/PS telegrams, at the application level (interface between bus interface module and application) as an extension to the bus protocol according to EN 50 170. Since configuring of communication is identical for both system buses, the PROFIBUS-TM bus can the connected to the CS 275 bus via the CS-L2 bridge.

A data transmission rate of 1.5 Mbit/s is used for communication between the TELEPERM M components via the PROFIBUS-TM bus.

Despite the much higher data transmission rate compared to the CS 275, only the same performance data are guaranteed for the PROFIBUS-TM as for the CS 275 bus system. The reason is that multi-address orders such as AKS, BKS and MKS are resolved into individual telegrams in the case of PROFIBUS-TM, and these types of telegram therefore require far higher communica- tion resources.

However, if the multi-address orders only have a few addresses, and if more single address orders (e.g. read/write parameters) are present compared to the multi-address orders, the perfor- mance of the PROFIBUS-TM bus system is higher than that of the CS 275. However, the degree can only be determined by a bus analysis.

Transmission systems

PROFIBUS offers a comprehensive range of network compo- nents for electrical and optical transmission systems.

•Electrical network

Shielded, twisted two-wire cables are used for electrical PROFIBUS networks. The RS 485 interface operates using voltage differences. It is therefore less sensitive to interferenc- es than a voltage or current interface. With PROFIBUS, the sta- tions are connected to the bus cable via a bus connector or bus terminal.

The individuals segments are connected using repeaters.

•Optical network

The optical version of the PROFIBUS is suitable for long dis- tances, and is insensitive to electromagnetic interferences. Glass fiber-optic cables are preferably used. Plastic fiber-optic cables can also be used for lower demands (short distances). The stations are connected to the optical PROFIBUS network via an optical link module (OLM). The optical transmission link can be up to 21 km long, or up to 16 km when using a CS-L2 bridge.

The OLM can be used to design an optical network with a mul- tipoint, ring or star structure.

•Mixed network

Mixed structures are possible comprising electrical and optical PROFIBUS networks. OLMs are used for the transition between the two media.

There is no difference between the electrical two-wire and optical systems as far as communication between the stations is concerned.

Possible bus configuration: linear and tree structures of the PROFIBUS electrical network

9/2	Siemens PLT 112 · 2002