Profibus DP interface definition Profibus-DP communication protocol overview

1. Overview

PROFIBUS-DP stands for Decentralized Periphery, which is a computer electronic component. It has high speed and low cost, and is used for communication between device-level control systems and distributed I/O. It, PROFIBUS-PA (Process Automation) and PROFIBUS-FMS (Fieldbus Message Specification) together form the PROFIBUS standard.

2. Basic Information

Industry regulations

The PROFIBUS-DP protocol clearly defines how user data is transmitted between bus stations, but the meaning of user data is specifically described in the PROFIBUS profile. In addition, the profile also specifies how PROFIBUS-DP is used in application areas. The use of profiles allows different devices produced by different manufacturers to be used interchangeably, and factory operators do not need to worry about the differences between the two. This is because the application-related meanings are precisely defined in the profile. The following is the PROFIBUS-DP profile, and the numbers in brackets are the file numbers: (1) NC/RC profile (3.052) (2) Encoder profile (3.062) (3) Variable speed drive profile (3.071) (4) Operator control and process monitoring profile (HMI)

Transmission distance

The transmission rate of Profibus is 9.6K~12Mbps, and the maximum transmission distance is 1000m at 9.6K~187.5Kbps, 400m at 500Kbps, 200m at 1500Kbps, and 100m at 3000K~12000Kbps, which can be extended to 10km with a repeater. The transmission medium can be twisted pair or optical cable, and up to 127 stations can be connected.

Profibus is a fieldbus that is a German national standard DIN 19245 and a European standard prEN 50170. The ISO/OSI model is also its reference model. The Profibus series consists of Profibus-Dp, Profibus-FMS, and Profibus-PA. The DP type is used for high-speed transmission between distributed peripherals and is suitable for applications in the field of processing automation. FMS means field information specification, which is suitable for general automation such as textiles, building automation, programmable controllers, and low-voltage switches, while PA is a bus type used for process automation, which complies with the IEC1158-2 standard.

This technology was jointly launched by more than a dozen German companies and research institutes, mainly Siemens. It uses the physical layer and data link layer of the OSI model, and these two parts form a subset of the first part of its standard. The DP type hides layers 3 to 7 and adds direct data connection fitting as a user interface. The FMS type only hides layers 3 to 6 and uses the application layer as the second part of the standard.

The standard of PA type is still under development. Its transmission technology complies with IEC1158-2 (1) standard and can realize bus power supply and intrinsic safety explosion protection. Profibus supports several transmission modes, such as master-slave system, pure master station system, and multi-master and multi-slave mixed system. The master station has the control right of the bus and can actively send information. For the multi-master station system, the master stations use tokens to transmit information. The station that obtains the token can have the control right of the bus within a predetermined time. The maximum time for the token to circulate in each master station is predetermined in advance.

According to the communication specification of Profibus, the token is transmitted in the upstream direction between the master stations in the order of address number. When the master station obtains the control right, it can send or request information to the slave station in the master-slave mode to realize point-to-point communication. The master station can broadcast to all stations (without requiring a response) or selectively broadcast to a group of stations.

Extended functionality

DP extended functions are a supplement to DP basic functions and are compatible with DP basic functions.

(1) Acyclic data transmission between DPM1 and DP slaves.

(2) Acyclic read/write functions with DDLM read and DDLM write, which can read and write any desired data from the slave.

(3) Alarm response. DP basic functions allow DP slaves to spontaneously transmit events to the master with diagnostic information, while the newly added DDLM-ALAM-ACK function is used to directly respond to alarm data received from DP slaves.

(4) Acyclic data transmission between DPM2 and slaves.

Data files

In order to integrate PROFIBUS products produced by different manufacturers, manufacturers must store the functional parameters of these products (such as I/O points, diagnostic information, baud rate, time monitoring, etc.) in the form of GSD files (electronic device database files). Standard GSD data expands communication to the operator control level. Using configuration tools based on GSD, devices produced by different manufacturers can be integrated into the same bus system.

The GSD file can be divided into three parts:

(1) General Specifications: Includes manufacturer and device name, hardware and software versions, baud rate, monitoring time interval, and bus plug specified signals.

(2) DP-related specifications: including various parameters applicable to the master station, such as the number of slave stations allowed and upload/download capabilities.

(3) Specifications related to DP slaves: Includes all specifications related to slaves, such as number of input/output channels, type, diagnostic data, etc.

3 GSD file format

GSD files are ASCII files. They can be edited with any ASCII editor such as Notepad, UltraEdit, etc., or with the editing program GSDEdit provided by the PROFIBus user organization. GSD files are composed of several lines, each of which begins with a keyword, including keywords and parameters (unsigned numbers or strings). Keywords in GSD files can be standard keywords (defined in the PROFIBUS standard) or user-defined keywords. Standard keywords can be recognized by any PROFIBUS configuration tool, while user-defined keywords can only be recognized by specific configuration tools.

An example of a GSD file is shown below.

#Profibus DP; GSD files of DP devices all exist with this key

GSD Revision=1; GSD file version

VendorName="Meglev" ; Equipment manufacturer

Model Name="DP Slave" ；Product Name

Revision="Version 01" ; product version

RevisionNumber=01; Product version number (optional)

IdemNumber=0x01; Product identification number

ProtocoI Ident=0; Protocol type (indicates DP)

StationType=0; station type (0 means slave station)

FMS Supp=0; does not support FMS. Pure DP slave

Hardware Realease="HW1.0" ; Hardware version

Soltware Realease="SWl.0"; Software version

9.6 supp=1; support 9.6kbps baud rate

19.2 supp=l; support 19.2kbps baud rate

MaxTsdr 9.6=60; Maximum delay time at 9.6kbps

MaxTsdrl9.2=60; Maximum delay time at 19.2kbps

RepeaterCtrl sig=0; RTS signal is not provided

24VPins=0; 24V voltage is not provided

Implementation Type="SPC3" ; Solution adopted

FreezeMode Supp=0; Lock mode is not supported

SyncMode Supp=0; Synchronous mode is not supported

AutoBaud Supp=l; support automatic baud rate detection

Set SlaveAdd Supp=0; does not support changing the slave address

Fail Safe=0; Fail safe mode type

MaxUser PrmDataLen=0; Maximum user parameter data length (0-237)

Usel prmDataLen=0; User parameter length

Min Slave Imervall=22; Minimum slave response cycle interval

Modular Station=l; Is it a modular station?

MaxModule=l; Maximum number of modules in the slave station

MaxInput Len=8; Maximum input data length

MaxOutput Len=8; Maximum output data length

MaxData Len=16; Maximum data length (sum of input and output)

MaxDiagData Len=6; Maximum diagnostic data length (6~244) Slave

Family=3; slave type

Module = "Module1" 0x23, 0x13; Module 1, 4 bytes for input and output

EndModule

Module="Module2"0x27, 0x17; Module 2. Input and output are 8 bytes each

EndModule

3. Function

Used for high-speed data transmission at the field level. The master station periodically reads the input information of the slave station and periodically sends the output information to the slave station. The bus cycle time must be shorter than the master station (PLC) program cycle time. In addition to periodic user data transmission, PROFIBUS-DP also provides non-periodic communication required by intelligent devices for configuration, diagnosis and alarm processing.

① Transmission technology: RS-485 twisted pair, two-wire cable or optical cable. Baud rate from 9.6K bit/s to 12M bit/s.

② Bus access: token transfer between master stations, master-slave transmission between master station and slave station. Support single master or multi-master system. The maximum number of stations (master-slave devices) on the bus is 126. The theoretical address range of Profibus: 0~127 (127 is the broadcast address). Up to 32 master stations can be used, and the total number of stations can reach 127 (multi-master).

③ Communication: point-to-point (user data transmission) or broadcast (control instructions). Cyclic master-slave user data transmission and non-cyclic master-master data transmission.

④Operation mode: Run. Clear. Stop.

⑤Synchronization: Control instructions allow input and output synchronization. Synchronization mode: output synchronization; Locking mode: input synchronization.

⑥Function: Cyclic user data transmission between DP master and DP slave. Dynamic activation and activatability of each DP slave. Checking of DP slave configuration. Powerful diagnostic function, three-level diagnostic information. Synchronization of input or output. Addressing of DP slaves via bus. Configuration of DP master (DPM1) via bus line, maximum input and output data of each DP slave is 244 bytes.

⑦ Reliability and protection mechanism: All information is transmitted according to the Hamming distance HD = 4. The DP slave station has a watchdog timer. The DP slave station input/output is protected. The DP master station has a variable timer for user data transmission monitoring.