An Introduction to Profibus DP Networking

To understand the technical design of Profibus DP, one must understand the PLC Scan Cycle, and how it is enabled by the Backplane of modular rack based PLCs.

An example of a orange juice bottling line is used to show how Profibus DP is used to reduce costs, installation time and errors. In addition, it results in a system that is easier to maintain.

We look at the meaning of the term Profibus DP and what a typical Profibus DP network looks like.

Siemens is the heaviest user of Profibus DP in the world. Working with Profibus DP on a practical level means that you will be interacting with Siemens PLC equipment.

An example diagram is used to illustrate the typical network layout and structure of a Profibus DP network. Similarities to a Modbus RS485 network are show to exist.

Typically, the address of Profibus DP slave devices are set using hardware switches on the device itself. However, there are exceptions to this. The address of the Profibus DP master device is typically set through software.

There are special reserved addresses that are used on the Profibus network.

Number of start bits, parity and number of stop bits are standardized in Profibus DP. Baud rate is configurable.

The baud rate used is determined by the slowest device on the network.

If the number of devices on a Profibus DP network exceeds 32, then repeaters must be used.

Cabling standard that is used on a Profibus DP network.

A typical Profibus DP connector is shown and the various functions discussed.

A look at various types of Profibus DP connectors.

The function of the bus termination switch is illustrated as well as it's proper usage on the network.

This lecture outlines the 7 steps that are used to create a Profibus DP network. Those same steps will be further expanded in the remainder of this section.

The profibus planning software is used to create a map of all of the slave devices on the profibus network, so that the master can use this information to communicate with the slave devices on the network.

What a GSD file is, what it is for and how it is used. These topics are explored in this lecture.

We go to the site of an automation vendor and download a GSD file, open it and examine the contents.

A screenshot of the Siemens Profibus planning tool is used to illustrate the concept of adding devices.

Installation files are downloaded and ImDisk is used to mount a new virtual drive from an ISO image.

Installation process is executed.

The first Profibus DP project we will be doing will involve programming a simple Profibus DP network with a S7-315 as the master and a ET200S as the slave.

Simatic Manager is started. A new project is created and the S7-315 is added as the Profibus DP master device.

The slave device is added, then the parameters are set. Finally, the I/O addresses mapping is performed.

The hardware configuration is downloaded into the CPU and the network is started. The network is then tested.

Some I/O is not read into the process image. Instead it is read directly to be used in the plc program. It is know as Peripheral Addressing.

Bus Faults and Diagnostic Messages - Part 1

Bus Faults and Diagnostic Messages - Part 2

An I/O module from Softlink is connected to the network. The GSD file is then uploaded into the HW config.

The network configuration is downloaded and run. Then tests are done for errors.

A Profibus DP network project is created to be used with the S7-PLCSIM simulator.

The Profibus DP configuration downloaded into the S7-PLCSIM simulator and then a bus fault is simulated.

A simple PLC application is written and is simulated. Then a bus fault is created and we see how the system responds.

The Profibus DP slave typically moves through 4 states during it's startup sequence.

A slave has a watchdog timer that is used to detect timeouts in communication with the DP master.