PROFIBUS – DP
DP of PROFIBUS-DP is Decentralized Periphery. It has high speed and low cost, and is used for communication between device-level control systems and distributed I / O. It forms the PROFIBUS standard together with PROFIBUS-PA (Process AutomaTIon) and PROFIBUS-FMS (Fieldbus Message SpecificaTIon).
Introduction
1. The role of PROFIBUS -DP
High-speed data transmission at the field level. The master station periodically reads input information from the slave station and periodically sends 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 acyclic communication required by intelligent devices for configuration, diagnosis, and alarm processing.
â‘ Transmission technology: RS-485 twisted pair. Two-wire cable or optical cable. The baud rate is from 9.6K bit / s to 12M bit / s.
â‘¡ Bus access: token transfer between master stations, master-slave transmission between master station and slave station. Support single or multi-master system. The number of the most stations (master-slave devices) on the bus is 126.
â‘¢Communication: point-to-point (user data transmission) or broadcasting (control instruction). Cyclic master-slave user data transfer and acyclic master-master data transfer.
â‘£ Running mode: run, clear, stop.
⑤ Synchronization: The control command allows input and output to be synchronized. Synchronization mode: output synchronization; lock mode: input synchronization.
â‘¥Function: cyclic users between DP master station and DP slave station have data transmission. Dynamic activation and activation of each DP slave. DP slave configuration check. Powerful diagnosis function, three-level diagnosis and diagnosis information. Synchronization of input or output. Give addresses to DP slaves via the bus. The DP master station (DPM1) is configured through the line, and the input and output data of each DP slave station is up to 246 bytes.
⑦ Reliability and protection mechanism: All information is transmitted according to Hamming distance HD = 4. DP slave with watchdog timer (Watchdog TImer). Access protection for the input / output of DP slaves. User data transfer monitoring with variable timers on the DP master.
⑧ Device type: The second type DP master (DPM2) is a device that can be programmed, configured and diagnosed. The first type of DP master station (DPM1) is a central programmable controller, such as PLC.PC, etc. DP slaves are drives with binary values ​​or analog inputs and outputs, valves, etc.
(1)
â‘ Speed: In a distributed system with 32 stations, PROFIBUS-DP transmits 512 bit / s input and 512 bit / s output to all stations, and it takes only 1 millisecond at 12Mbit / s.
â‘¡ Diagnosis function: The extended PROFIBUS-DP diagnosis can quickly locate the fault. Diagnostic information is transmitted on the bus and collected by the master station. The diagnostic information is divided into three levels:
· Diagnostic operation of this station: the general operating state of the equipment of this station, such as high temperature and low pressure.
· Module diagnosis operation: a specific I / O module of a station is faulty.
· Operation through diagnosis: failure of a single input / output bit.
(2)
PROFIBUS-DP allows to form a single master station or a multi-master system. Up to 126 stations can be connected on the same bus. The description of the system configuration includes: station number, station address, input / output address, input / output data format, diagnostic information format, and bus parameters used. Each PROFIBUS-DP system can include the following three types of devices of the same type:
â‘ First-level DP master station (DPM1): The first-level DP master station is the central controller, which exchanges information with decentralized stations (such as DP slave stations) within a predetermined period. Typical DPM1 such as PLC or PC.
â‘¡ Second-level DP master station (DPM2): The second-level DP master station is a programmer. Configuration device or operation panel is used during DP system configuration operation to complete system operation and monitoring purposes.
â‘¢ DP slave station: DP slave station is a peripheral device (I / O device, driver, HMI, valve, etc.) that collects and sends input and output information.
â‘£ Single master station system: In the operation phase of the bus system, there is only one active master station.
⑤ Multi-master system: There are multiple master stations connected to the bus. These master stations and their slave stations form independent subsystems. Each subsystem includes a DPMI. Designated number of slaves and possible DPM2 equipment. Any master station can read the input / output image of the DP slave station, but only one DP master station allows writing data to the DP slave station.
(3)
System behavior
The system behavior mainly depends on the operating state of DPM1, which is controlled by the local or bus configuration device. There are three main states:
· Stop: In this state, there is no data transmission between DPM1 and DP slave.
• Clear: In this state, DPM1 reads the input information of the DP slave and keeps the output information in a fail-safe state.
· Operation: In this state, DPM1 is in the data transmission stage. During cyclic data communication, DPM1 reads input information from the DP station and writes output information to the slave station.
â‘ The DPM1 device periodically sends its local status to each DP slave station in a predetermined broadcast interval in a selective broadcast mode.
â‘¡ 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 slave will not send user data. After this time, DPM1 transitions to the clear state.
(4)
Cyclic data transmission between DPM1 and DP slaves
User data transmission between DPM1 and the relevant DP slaves is automatically performed by DPM1 in the determined recursive order. When configuring the bus system, the user specifies the relationship between DP slaves and DPM1, and determines which DP slaves are included in the information exchange cycle and which are excluded.
The data transfer between DMP1 and DP slaves is divided into three stages: 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, the DP slave station enters the user data transmission phase. Therefore, the device type, data format, length, and number of inputs and outputs must be consistent with the actual configuration.
(5)
Cyclic data transmission between DPM1 and system configuration equipment
In addition to the master-slave functions, PROFIBUS-DP allows data communication between the master and the master. These functions enable the configuration and diagnostic equipment to configure the system via the bus.
(6)
Sync and lock mode
In addition to the cyclic transmission of user data automatically performed by the DPM1 device, the DP master device can also send control commands to individual DP slaves, a group of slaves, or all slaves. These commands are sent through selective broadcast commands. Using this function will open the synchronization and lock mode of DP slaves, which is used for event control synchronization of DP slaves.
After the master station sends the synchronization command, the selected slave station enters the synchronization mode. In this mode, the addressed slave output data is locked in the current state. In the user data transmission cycle after this, the slave station stores the received data, but its output status remains unchanged; when the next synchronization command is received, the stored output data is sent to the peripheral device. The user can exit the synchronous mode through an asynchronous command.
The lock control command causes the addressed slave to enter lock mode. The lock mode locks the input data of the slave station in the current state, and cannot be updated until the master station sends the next lock command. The user can exit the lock mode through a non-lock command.
(7)
protection mechanism
The DP master station DPM1 uses the data control timer to monitor the data transmission from the slave station. Each slave station uses an independent control timer. During the specified monitoring interval, if an error occurs in data transmission, the timer will time out. Once a timeout occurs, the user will get this information. If the error auto-reaction function is "enabled", DPM1 will leave the operating state and put the outputs of all associated slaves into a fail-safe state and enter the clear state.
2. Expand DP function
The DP extension function is a supplement to the DP basic function and is compatible with the DP basic function.
(1) Acyclic data transmission between DPM1 and DP slaves.
(2) Acyclic read / write function with DDLM read and DDLM write, can read and write any desired data from the slave station.
(3) Alarm response, the DP basic function allows DP slaves to use diagnostic information to spontaneously transmit events to the master, and 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 slave stations.
3. Electronic Device Data File (GSD)
In order to integrate PROFIBUS products produced by different manufacturers, manufacturers must use GSD files (electronic device database files) to function parameters of these products (such as I / O points, diagnostic information, baud rate, time monitoring, etc.) Standard GSD data extends communication to the level of operator control. The configuration tools made according to GSD can be used to integrate devices from different manufacturers into the same bus system.
The GSD file can be divided into three parts:
(1) General specification: including manufacturer and equipment name, hardware and software version, baud rate, monitoring time interval, bus plug designation signal.
(2) Specifications related to DP: including various parameters applicable to the master station, such as the number of allowed slave stations. Upload / download capacity.
(3) Specifications related to DP slaves: including all specifications related to slaves, such as the number of input / output channels, types, diagnostic data, etc.
4. PROFIBUS-DP profile
The PROFIBUS-DP protocol clearly stipulates how user data is transferred between the bus stations, but the meaning of user data is specified in the PROFIBUS profile. In addition, the regulations also specify how PROFIBUS-DP is used in the application field. The use of the rules allows different equipment produced by different manufacturers to be used interchangeably, and plant operators do not need to care about the differences between the two. Because the meanings related to the application are specified in the rules. The following is the PROFIBUS-DP profile, the numbers in parentheses are the file numbers:
(1) NC / RC regulations (3.052)
(2) Encoder profile (3.062)
(3) Variable speed drive profile (3.071)
(4) Operator control and process monitoring regulations (HMI)
5. PROFIBUS-DP transmission distance
The transmission rate of Profibus is 96 ～ 12kbps. The maximum transmission distance is 1000m at 12kbps and 400m at 15Mbps, and it can be extended to 10km with repeaters. The transmission medium can be twisted pair or fiber optic cable, and up to 127 sites can be connected.
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