Is there an overview for Profibus communication protocol?

Document ID

Document ID TE3852

Published Date

Published Date 27/05/2017
Question
Is there an overview for Profibus communication protocol?
Summary
Profibus DP features and specifications.
Answer
PROFIBUS originated in the European market and has become a worldwide standard because of its performance attributes. PROFIBUS consists of several variations, which are designed for use in special applications. The two PROFIBUS versions most commonly used are PROFIBUS-DP (Distributed Peripherals) and PROFIBUS-PA (Process Automation).
 
PROFIBUS-DP is recognized as a high performance bus network capable of transmitting thousands of I/O point information in less than a few milliseconds. For that reason it has been used extensively for fast response control applications such as turbine servos and variable speed drives.
 
PROFIBUS-PA was developed to connect directly into PROFIBUS-DP and may be used in intrinsically safe applications. DP uses the RS485 physical layer while PA uses the IEC 61158-2 physical layer designed primarily for process applications.
 
 

PROFIBUS-DP Features

 
•High speed data access capable of handling time critical functions.
•Networks up to 32 devices (up to 126 with repeaters) on a 4-wire network; (2-wires for signal and 2 wires for power).
•Trunk network may extend up to 4,000 feet (1220 meters) per segment.
•Dramatically cuts wiring costs and commissioning over conventional applications.
• Interfaces readily into newer control systems.
•Used extensively throughout Europe with support in North America.
 
 

PROFIBUS-DP Description

 
The DP version of PROFIBUS uses the RS485 physical layer with its unique data link layer and a direct data link mapper connecting the data link layer directly to application functions.
 
PROFIBUS uses a medium access control which includes token-passing for multimaster applications and the master slave interaction. Networks may be multi-master, multimaster with slaves, or single-master with slaves. In a multimaster network the token is passed to each master in a predetermined time frame. The master with the token is active and communicates with other masters or accesses its assigned slaves.
 
Communication occurs on a peer-to-peer basis for data communication or on a multi-cast basis for control commands. Cyclic polling may also be used for data communication between the master and its designated slaves. DP also offers a cyclic communication services for the parameterization, operation, monitoring, and alarm handling of intelligent field devices. These a cyclic services may be handled in parallel to data transfer with the master taking some additional time to carry out this function. A cyclic extended functions are optional.
 
PROFIBUS-DP handles large amounts of I/O data at very high speeds. DP requires about 1 millisecond to handle 1024 I/O points over 32 devices at the 12 Mbit/sec rate. This is possible due to the efficient mapping of the data from the data link layer directly to the user layer by means of the SRD service of the data link layer.
 
For configuration of DP devices a GSD file (Electronic device data sheet) is used which describes the characteristics of a device type in a precisely defined format. Vendors provide specific GSD files to users. The system simply reads the GSD file for each device and automatically configures the bus system using this information.
 
An EDD (Electronic Data Description) file, which is not vendor specific, is also used to describe each device. These files, also provided by vendors, are read by the engineering tools to simplify the Profibus systems configuration, commissioning, and maintenance.
 
PROFIBUS-DP Specifications:
Physical Layer RS-485
Cabling One shielded twisted pair for signal and one pair for 24 VDC supply
Topology Trunk with Drops
Cable Length (meters) /baud rate (Kbits/sec) 1200/93.75, 1000/187.5, 400/600, 200/1500, 100/12000
Number of Devices 32 per segment: Up to 126 with 4 repeaters
Bus Power Must have auxiliary 24VDC supply
Transmission Rate 9.6 K to 12 M bits/second
Data Access Token sharing for multi-masters; peer-to-peer data transfer: multicast and cyclic polling for data transfer: a cyclic for asset management
Data Transfer Size Up to 246 Bytes of Input & 246 Bytes of Output Depending on Device Type
Device Identity Specific ID number for each device
Error Detection HD4 CRC (Cyclic Redundancy Check)
Support Organization PROFIBUS Users Group www.profibus.com
 
 

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