PROFIBUS PROTOCOL: Introduction
PROFIBUS PROTOCOL is not a communication system, but a variety of protocols integrated in the same fieldbus technology package. Users can combine a variety of PROFIBUS protocols with their own software and other requirements, resulting in a unique application profile. With many profiles available, PROFIBUS PROTOCOL can meet specific needs. However, one thing remains the same. Through extensive testing, PROFIBUS devices meet a high quality standard consistent with a high quality network.
PROFIBUS PROTOCOL was born out of a joint push by the German government, German companies and other industry leaders in the late 1980s. Their efforts created an automation solution that not only is still viable today, but has led to other solutions. The proud legacy of PROFIBUS allows many European customers to turn to specific automation for their needs.
In 1987, 21 companies and institutions in Germany joined forces to create a new protocol. Their goal was to create a bit-serial Fieldbus system. In order for the system to be viable, they had to standardize the field device interface. The group, which had assumed the name of the Central Association for the Electric Industry (ZVEI), completed its goal with the creation of PROFIBUS FMS (Fieldbus Message Specification).
This new protocol has satisfied the standardization of industrial automation through a protocol capable of sending complex communications. In most environments, PROFIBUS PA works on RS485 twisted pair supports. This support, together with the PA application profile, supports bus power. However, in explosive environments, that power can cause sparks that induce explosions. For this purpose, PROFIBUS PA can be used with Manchester Bus Powered (MBP) technology
However, the ZVEI was not finished. In 1993 the group introduced a new standard, PROFIBUS DP (decentralized periphery). This new version introduced greater simplicity, including simpler configuration and faster messages.
ZVEI continues to serve the electronics industry in Germany. His work on creating PROFIBUS has been vital.
PROFIBUS PROTOCOL standards are maintained and advanced through a couple of major organizations. In 1989, PROFIBUS manufacturers and users created the PROFIBUS User Organization (PNO). This group was and still is a non-commercial company. Members work to advance PROFIBUS through support and training, including the publication of documents that help users meet their needs using existing technology.
A larger group was formed in 1995 and was called PROFIBUS PROTOCOL International, or PI. Being the largest association of Fieldbus users in the world, PI can carry out many activities vital for the progression of PROFIBUS. Like PNO, PI informs users about PROFIBUS and helps to advance their position in the world. However, the organization goes further by helping with quality assurance, setting standards and developing new PROFIBUS technologies.
PROFIBUS is an intelligent fieldbus technology. The devices in the system are connected to a central line. Once connected, these devices can communicate information efficiently, but they can go beyond automation messages. PROFIBUS devices can also participate in self-diagnosis and connection diagnostics. At the most basic level, PROFIBUS benefits from the superior design of its OSI levels and its basic topology.
PROFIBUS networks use three separate layers of the OSI network model. PROFIBUS first describes the application level. There are multiple versions of PROFIBUS which handle different types of messages at the application level. Some of the message types supported by PROFIBUS include cyclic and acyclic data exchange, diagnostics, alarm management and isochronous messages.
PROFIBUS does not define levels three to six. However, it defines the data link and physical layers, layers one and two. The data link layer is completed via a fieldbus or FDL data link. The FDL system combines two common schemes, the master-slave methodology and the token transfer. In a master-slave network, masters, typically controllers, send requests to slaves, sensors and actuators. The slaves respond accordingly. PROFIBUS also includes passing tokens, In most environments, PROFIBUS PA works on RS485 twisted pair supports. This support, together with the PA application profile, supports bus power. However, in explosive environments, that power can cause sparks that induce explosions. For this purpose, PROFIBUS PA can be used with Manchester Bus Powered (MBP) technology
a system in which a “token” signal is passed between nodes. Only the node with the token can communicate. The concept of passing chip is like the talking shell; only the person with the shell can speak.
Finally, PROFIBUS defines a physical level, even if it leaves room for flexibility. PROFIBUS systems can have three types of media. The first is a standard twisted pair cabling system, in this case RS485. Two other advanced systems are also available. PROFIBUS systems can now work with fiber optic transmission where appropriate. An improved safety system called Manchester Bus Power, or MBP, is also available in situations where the chemical environment is subject to explosion.
PROFIBUS uses the bus topology. In this topology, a central line or bus is wired throughout the system. The devices are connected to this central bus. A bus eliminates the need for a full length line running from the central controller to each individual device.
In the past, each PROFIBUS device had to be connected directly to the central bus. Technological advances, however, have made possible a new “two-wire” system. In this topology, the PROFIBUS central bus can be connected to a ProfiNet Ethernet system. This allows multiple PROFIBUS buses to be connected together. In most environments, PROFIBUS PA works on RS485 twisted pair supports. This support, together with the PA application profile, supports bus power. However, in explosive environments, that power can cause sparks that induce explosions. For this purpose, PROFIBUS PA can be used with Manchester Bus Powered (MBP) technology
PROFIBUS advanced through a handful of reviews. In some cases, progress has led to a new type of PROFIBUS. In other cases, the new revisions mean different versions of the same type of PROFIBUS. In any case, the variety of PROFIBUS solutions allows you to adapt the system to the different needs of the different sectors.
The initial version of PROFIBUS was PROFIBUS FMS, specific to the Fieldbus message. PROFIBUS FMS has been designed to communicate between programmable controllers and PCs, sending complex information between them. Unfortunately, being the initial effort of PROFIBUS designers, FMS technology was not flexible enough. This protocol was not appropriate for less complex messages or communications on a larger and more complicated network. The new PROFIBUS types would meet
these needs. PROFIBUS FMS is still in use today, although the vast majority of users believe that the latest solutions are more appropriate.
The second type of PROFIBUS is more universal. Called PROFIBUS DP, with decentralized I / O, this new protocol is much simpler and faster. PROFIBUS DP is used in the vast majority of the PROFIBUS application profiles currently in use. Application profiles allow users to combine their requirements for a specific solution and will be discussed in more detail shortly.
PROFIBUS DP itself has three separate versions. Each version, from DP-V0 to DP-V1 and DP-V2, offers newer and more complicated features.
PROFIBUS PA is a protocol designed for process automation. PROFIBUS PA is currently a type of PROFIBUS DP application profile. PROFIBUS PA standardizes the transmission process of the measured data. However, it has a very important unique feature. PROFIBUS PA has been specifically designed for use in hazardous environments.
In most environments, PROFIBUS PA works on RS485 twisted pair supports. This support, together with the PA application profile, supports bus power. However, in explosive environments, that power can cause sparks that induce explosions. For this purpose, PROFIBUS PA can be used with Manchester Bus Powered (MBP) technology
The MBP support has been specially designed for use in PROFIBUS PA. Allows the transmission of data and power. However, the technology reduces the power. Lower power reduces, or almost eliminates, the possibility of explosion. Buses using MBP can reach 1900 meters and can support branches. Application profiles
PROFIBUS can be adapted to specific needs using the application profiles. There are many profiles that combine the standards for transmission media, the communication protocol (FMS, DP-V0, etc.) and the unique protocols. Each application profile is customized for a specific use and new profiles are displayed regularly. List them all would be cumbersome.
However, some application profiles are widespread. Two examples are PROFIsafe and PROFIdrive. PROFIsafe
PROFIsafe uses additional software to create a high integrity network. This network is useful in situations where high security is required. For suppliers and manufacturers they are PROFIsafe certified, they must maintain high quality requirements.
PROFIdrive was created for motion control applications. The software added to the PROFIBUS DP specification allows the network to obtain precise control of the servomotors and other equipment. Therefore PROFIdrive can achieve synchronization on the network.
The PROFIBUS user organization has created a compliance testing program to ensure that the devices meet high standards. In this program, a device is sent to an independent laboratory for analysis. Then the device undergoes a full set of tests, including hardware, compliance and functional tests, among others. The test results are documented.
When a device passes all tests, the manufacturer can request a certificate of conformity. The certificate is valid for three years and can be renewed with multiple tests.
|PRIMARY ADVANTAGES||Very Fast and Simple Integration to Siemens PLCs | Acceptance in Europe|
|PRIMARY ADVANTAGES||Expensive ASIC Required, No Power over the Bus, Expensive Connectors|
|NETWORK SPEED||12 Meg|
|DUPLICATE ADDRESS DETECTION||None|
|MAXIMUM FRAME SIZE||244 Bytes|
|CONNECTORS||Enhanced DB-9 for Profibus Speed|
|CONNECTORS||None – Half Duplex Protocol|
|BANDWIDTH UTILIZATION||Medium to Low | Frame Size larger than most applications require|
|MAXIMUM NUMBER NODES||126 with 32 Maximum per segment|
|MESSAGING TYPES||Two Types (Messaging and I/O)|
|PRIMARY COMMUNICATION METHODS||Half Duplex Master Slave|
|MAX I/O PER PACKET||244 Bytes|
|LARGE MESSAGE FRAGMENTATION||No|
|TYPICAL CYCLE TIMES||10 mec|
|SPONSORING ORGANIZATION||Profibus User Organization (PNO)|
|CONNECTOR COST||Expensive Drivers and Interface for 12Meg Speed|
|TYPICAL FLASH REQUIRED||ASIC Plus 5K in Processor|
|TYPICAL RAM REQUIRED||5K | Varies with I/O Supported|