Profibus Technology - Omron GRT1 - 27-11-2006 Operation Manual

Profibus communication unit

Table of Contents

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Overview of PROFIBUS

PROFIBUS (PROcess FIeldBUS) is an open fieldbus standard for a wide range of applications in manufactur-

ing, processing and building automation. The Standard, EN 50170 (the Euronorm for field communication), to

which PROFIBUS adheres, guarantees vendor independence and transparency of operation. It enables

devices of various manufacturers to intercommunicate without having to make any special interface adapta-

tions.

The PROFIBUS family comprises three mutually compatible versions:

• PROFIBUS FMS (for Fieldbus Message Specification) is the general-purpose solution for high-level exten-

sive and complex communication tasks. Powerful services open up a wide range of applications and pro-

vide great flexibility.

• PROFIBUS DP (for Decentralized Periphery) is a variant optimized for high speed and low-cost interfacing.

It is specially designed for communication between automation control systems and distributed I/O at the

device level.

• PROFIBUS PA (for Process Automation) is a variant which permits sensors and actuators to be connected

to one common bus even in areas where intrinsically safe products are required. It permits data and power

to be supplied over the bus using 2-wire technology according the international standard IEC 1158-2.

PROFIBUS DP and PROFIBUS FMS use the same transmission technology and uniform bus access protocol.

Consequently, both versions can be operated simultaneously on the same bus. FMS field devices, however,

cannot be controlled by DP masters and vice versa.

!CautionIt is not possible to exchange one of these family members by another family member. This will

cause faulty operation.

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PROFIBUS Communication Protocol

In general, the PROFIBUS communication protocol is based on the Open System Interconnection (OSI) refer-

ence model in accordance with the international standard ISO-7498 (see the following illustration). The model

defines 7 layers of communication functions, three of which - layers 1, 2, and 7 - are used in PROFIBUS.

User Interface Layer

(7) Application Layer

(6) Presentation Layer

(5) Session Layer

(4) Transport Layer

(3) Network Layer

(2) Data Link Layer

(1) Physical Layer

• Layer 1, the Physical Layer of this model, defines the physical transmission characteristics.

• Layer 2, the Data Link Layer of this model, defines the bus access protocol. This protocol also includes

data security and the handling of transmission protocols and telegrams.

• Layer 7, the Application Layer of this model, defines the application functions. This Layer is only applicable

to PROFIBUS FMS

In the rest of this Appendix, only PROFIBUS DP is considered.

Appendix A