PROFIBUS – DP stands for Decentralized Periphery, which is a type of computer electronic component. It features high speed and low cost, used for communication between device-level control systems and decentralized I/O. It, along with PROFIBUS-PA (Process Automation) and PROFIBUS-FMS (Fieldbus Message Specification), forms the PROFIBUS standard.
Standards
The PROFIBUS–DP protocol clearly defines how user data is transmitted among bus stations, with the meaning of user data specified in the PROFIBUS standards. Additionally, the standards specify how PROFIBUS–DP is used in application fields. Using standards allows devices from different manufacturers to be interchangeable without factory operators needing to worry about the differences between them. The meanings related to applications are precisely defined in the standards. Below are the PROFIBUS–DP standards, with numbers in parentheses denoting document numbers:
(1) NC/RC Standard (3.052)
(2) Encoder Standard (3.062)
(3) Variable Speed Drive Standard (3.071)
(4) Operator Control and Process Monitoring Standard (HMI)
Transmission Distance
The transmission rate of Profibus ranges from 9.6K to 12Mbps, with the maximum transmission distances being 1000m at 9.6K~187.5Kbps, 400m at 500Kbps, 200m at 1500Kbps, and 100m at 3000K~12000Kbps, which can be extended to 10km using repeaters. The transmission medium can be twisted pair cables or optical fibers, with a maximum of 127 stations connected.
Profibus is a fieldbus defined as the German national standard DIN 19245 and the 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. DP is used for high-speed transmission between decentralized peripherals, suitable for applications in processing automation. FMS refers to Fieldbus Message Specification, suitable for general automation such as textiles, building automation, programmable controllers, and low-voltage switches, while PA is the bus type used for process automation, following the IEC1158-2 standard. This technology was jointly launched by Siemens and several German companies and research institutes. It adopts the physical layer and data link layer of the OSI model, forming a subset of its first standard part, with DP omitting layers 3 to 7 and adding direct data connection as the user interface, while FMS only omits layers 3 to 6, adopting the application layer as the second part of the standard. The PA type standard is still in the process of being formulated, and its transmission technology follows the IEC1158-2 (1) standard, enabling bus power supply and intrinsic safety explosion-proof.
Profibus supports various transmission modes, including master-slave systems, pure master systems, and multi-master multi-slave hybrid systems. The master station has control over the bus and can actively send information. In a multi-master system, information is passed between masters using a token method, where the station receiving the token has control of the bus for a predetermined time, with a maximum cycle time for the token defined among all masters. According to the PROFIBUS communication specification, the token is passed among the masters in ascending order of address. When a master gains control, it can send or request information from the slave stations in a master-slave manner, achieving point-to-point communication. The master can broadcast to all stations (no response required) or selectively broadcast to a group of stations.
Extended Functions
DP extended functions supplement the basic DP functions and are compatible with them.
(1) Non-cyclic data transmission between DPM1 and DP slaves.
(2) Non-cyclic read/write functions with DDLM read and DDLM write, allowing reading and writing of any desired data from the slave.
(3) Alarm response, where the basic DP function allows DP slaves to spontaneously transmit events to the master using diagnostic information, while the newly added DDLM-ALAM-ACK function is used to directly respond to alarm data received from DP slaves.
(4) Non-cyclic data transmission between DPM2 and slaves.
Data Files
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 GSD files (electronic device database files). The standard GSD data expands communication to the operator control level. Using configuration tools based on GSD, devices from different manufacturers can be integrated into the same bus system.
GSD files can be divided into three parts:
(1) General specifications: including manufacturer and device names, hardware and software versions, baud rate, monitoring time intervals, and bus connector designated signals.
(2) DP-related specifications: including parameters applicable to masters, such as the number of allowed slaves and upload/download capabilities.
(3) DP slave-related specifications: including all specifications related to slaves, such as input/output channel numbers, types, diagnostic data, etc.
GSD files are ASCII files that can be edited with any ASCII editor such as Notepad, UltraEdit, etc., or using the editing program GSDEdit provided by the PROFIBUS user organization. A GSD file consists of several lines, each starting with a keyword, including both the keyword and parameters (unsigned numbers or strings). The keywords in GSD files can be standard keywords (defined in the PROFIBUS standard) or custom keywords. Standard keywords can be recognized by any configuration tool for PROFIBUS, while custom keywords can only be recognized by specific configuration tools.
An example of a GSD file is as follows.
#Profibus DP; GSD files for DP devices all start with this keyword
GSD Revision=1; GSD file version
VendorName=”Meglev”; Device manufacturer
Model Name=”DP Slave”; Product name
Revision=”Version 01″; Product version
RevisionNumber=01; Product version number (optional)
IdemNumber=0x01; Product identification number
Protocol Ident=0; Protocol type (indicating DP)
StationType=0; Station type (0 indicates slave)
FMS Supp=0; FMS not supported, pure DP slave
Hardware Realease=”HW1.0″; Hardware version
Soltware Realease=”SWl.0″; Software version
9.6 supp=1; Supports 9.6kbps baud rate
19.2 supp=1; Supports 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; No RTS signal provided
24VPins=0; No 24V voltage provided
Implementation Type=”SPC3″; Adopted solution
FreezeMode Supp=0; Locking mode not supported
SyncMode Supp=0; Synchronization mode not supported
AutoBaud Supp=1; Supports automatic baud rate detection
Set SlaveAdd Supp=0; Slave address change not supported
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=1; Whether it is a modular station
MaxModule=1; Maximum number of modules for the slave
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
Module=”Module1″0x23,0x13; Module 1, 4 bytes each for input and output
Module=”Module2″0x27,0x17; Module 2, 8 bytes each for input and output
Used for high-speed data transmission at the field level. The master station periodically reads the input information from the slave stations and periodically sends output information to the slaves. The bus cycle time must be shorter than the master (PLC) program cycle time. In addition to periodic user data transmission, PROFIBUS-DP also provides non-periodic communication required by intelligent devices for configuration, diagnostics, and alarm handling.
① Transmission technology: RS-485 twisted pair, double wire cable, or optical fiber. Baud rates range from 9.6K bit/s to 12M bit/s.
② Bus access: Token passing between masters, master-slave transmission between master and slaves. A maximum of 126 stations (master-slave devices) can be connected to the bus. The theoretical address range of Profibus is 0~127 (127 is the broadcast address). Up to 32 masters can be used, with a total station count reaching 127 (multi-master).
③ Communication: Point-to-point (user data transmission) or broadcast (control commands). Cyclic master-slave user data transmission and non-cyclic master-master data transmission.
④ Operating modes: Run, Clear, Stop.
⑤ Synchronization: Control commands allow input and output synchronization. Synchronization mode: output synchronization; locking mode: input synchronization.
⑥ Functions: Cyclic user data transmission between DP masters and DP slaves. Dynamic activation and reactivation of each DP slave. Configuration checks of DP slaves. Strong diagnostic functions, with three-level diagnostic information. Synchronization of inputs or outputs. Assigning addresses to DP slaves via the bus. Configuring DP masters (DPM1) through sub-lines, with each DP slave’s input and output data having a maximum of 244 bytes.
⑦ Reliability and protection mechanisms: All information transmission follows a Hamming distance HD=4. DP slaves are equipped with watchdog timers. Access protection for DP slave inputs/outputs. User data transmission monitoring on DP masters with variable timers.
⑧ Device types: The second type of DP master (DPM2) is programmable, configurable, and diagnostic. The first type of DP master (DPM1) is a central programmable controller, such as PLC, PC, etc. DP slaves are drives, valves, etc., with binary or analog input/output; they can also be intelligent slaves, meaning they support programmability, generally another PLC host.
Rate Diagnostics
① Rate: In a distributed system with 32 stations, PROFIBUS-DP transmits 512 bit/s of input and 512 bit/s of output to all stations, requiring only 1 millisecond at 12Mbit/s.
② Diagnostic functions: The extended PROFIBUS-DP diagnostics can quickly locate faults. Diagnostic information is transmitted on the bus and collected by the master. Diagnostic information is divided into three levels:
· Local station diagnostics: General operating status of the local device, such as high temperature or low pressure.
· Module diagnostics: A specific I/O module failure at a station.
· Through diagnostic operations: A failure of a single input/output bit.
System Composition
PROFIBUS-DP allows for the construction of single-master or multi-master systems. A maximum of 126 stations can be connected on the same bus. The description of system configuration includes: number of stations, station addresses, input/output addresses, input/output data formats, diagnostic information formats, and bus parameters used. Each PROFIBUS-DP system can include the following three different types of devices:
① First-level DP master (DPM1): The first-level DP master is the central controller that exchanges information with decentralized stations (such as DP slaves) in predetermined cycles. Typical DPM1s include PLCs or PCs.
② Second-level DP master (DPM2): The second-level DP master is a programmer, configuration device, or operator panel used during DP system configuration operations to achieve system operation and monitoring purposes.
③ DP slave: DP slaves are peripheral devices (I/O devices, drivers, HMIs, valves, etc.) that collect and send input and output information.
④ Single-master system: During the operating phase of the bus system, there is only one active master.
⑤ Multi-master system: Multiple masters are connected on the bus. These masters form mutually independent subsystems with their respective slaves. Each subsystem includes one DPM1, a specified number of slaves, and possibly DPM2 devices. Any master can read the input/output image of the DP slaves, but only one DP master is allowed to write data to the DP slaves.
System Behavior
System behavior mainly depends on the operating state of DPM1, which is controlled by local or bus configuration devices. There are three main states:
· Stop: In this state, there is no data transmission between DPM1 and DP slaves.
· Clear: In this state, DPM1 reads the input information from DP slaves and keeps the output information in a fail-safe state.
· Run: In this state, DPM1 is in the data transmission phase, cyclically reading input information from DP stations and writing output information to slaves.
① The DPM1 device periodically sends its local status to each relevant DP slave in a selective broadcast manner at a predetermined time interval.
② If an error occurs during the data transmission phase of DPM1, DPM1 immediately transfers the output data of all relevant DP slaves to the clear state, and the DP slaves will not send user data. After this, DPM1 enters the clear state.
Cyclic Data
The user data transmission between DPM1 and related DP slaves is automatically performed by DPM1 in a predetermined recursive order. When configuring the bus system, the user specifies the relationship between DP slaves and DPM1, determining which DP slaves are included in the information exchange cycle and which are excluded.
The data transmission between DPM1 and DP slaves occurs in three phases: parameter setting, configuration, and data exchange. In the parameter setting phase, each slave compares its actual configuration data with the configuration data received from DPM1. Only when the actual data matches the required configuration data does the DP slave enter the user data transmission phase. Therefore, the device type, data format, length, and input/output quantity must match the actual configuration.
Configuration Devices
In addition to master-slave functionality, PROFIBUS-DP allows for data communication between masters, enabling configuration and diagnostic devices to configure the system via the bus.
Locking Mode
In addition to the cyclic data transmission automatically performed by DPM1 devices, DP master devices can also send control commands simultaneously to individual DP slaves, a group of slaves, or all slaves. These commands are sent through selective broadcast commands. Using this function opens the synchronization and locking modes of DP slaves for event control synchronization.
After the master sends a synchronization command, the selected slaves enter the synchronization mode. In this mode, the addressed slaves’ output data is locked in the current state. During the subsequent user data transmission cycle, the slaves store the received output data, but their output state remains unchanged; the stored output data is only sent to the peripheral devices upon receiving the next synchronization command. Users can exit the synchronization mode via non-synchronization commands.
Locking control commands cause the addressed slaves to enter the locking mode. The locking mode locks the input data of the slaves in the current state, allowing updates only when the master sends the next locking command. Users can exit the locking mode via non-locking commands.
Protection Mechanism
The DP master DPM1 uses a data control timer to monitor the data transmission of slaves. Each slave adopts an independent control timer. If an error occurs during data transmission within the specified monitoring interval, the timer will time out. Once a timeout occurs, the user will be informed. If the automatic response function for errors is enabled, DPM1 will exit the operating state, set all associated slaves’ outputs to fail-safe state, and enter the clear state.
