New summary of Profibus DP
1. Introduction to PROFIBUS-DP
DP is the abbreviation of Decentralized Periphery (Distributed Periphery). PROFIBUS-DP (abbreviated as DP) is mainly used for unit-level and field-level communication in manufacturing automation systems. It is especially suitable for fast cycle data exchange between PLC and field-level distributed I/O devices. DP is the most widely used communication method in PROFIBUS.
Profibus_Dp (Decentralized Peripheral, decentralized peripherals) is an optimized, high-speed and low-cost communication connection. It is designed for the communication between automatic control systems and device-level decentralized I/O. It can be replaced by PROFIBUS-DP Expensive 24V or 0-20mA parallel signal line. It is used for high-speed data transmission of distributed control system, and its data transmission rate can reach 12Mbps. Most of the data exchange between the automatic control system and these scattered peripherals (sensors, actuators, etc.) is periodic, and generally constitutes a single-master station system, with cyclic data transmission between the master and slave stations.
PROFIBUS-DP is used to connect the following equipment: PLC, PC and HMl equipment, distributed field equipment. PROFIBUS-DP has a fast response speed and is very suitable for use in the manufacturing industry.
As part of the PLC hardware configuration, distributed I/O (such as ET200) is configured with STEP7. Through the GSD file provided by the supplier, you can use STEP7 to configure slave devices produced by other manufacturers into the network.
Some S7-300/400 CPUs are equipped with an integrated DP interface, and S7-200/300/400 can also be connected to PROFIBUS-DP through a communication processor (CP).
2. PROFIBUS-DP function
2.1 Profibus_Dp
Profibus_Dp is designed to be used for high-speed data transmission at the field level. At this level, the central controller (PLC) communicates with scattered field devices (such as IOs, drives, gates, etc.) through high-speed serial lines, and data exchange with these scattered devices is mostly cyclic. In addition to performing these cyclic functions, intelligent field devices also need acyclic communication for configuration, diagnosis, and alarms. These acyclic functions are extensions of the basic functions of Profibus_Dp.
The basic function of profibus PLC periodically reads the input information of the device and periodically wants to send output information from the device. The bus cycle time is shorter than the PLC cycle time. Profibus_Dp provides powerful diagnostic functions and configuration functions.
(1) Transmission technology: According to the difference of the maximum transmission rate, two transmission media of RS485 twisted pair two-wire cable and optical cable can be selected. The baud rate is from 9.6K-12Mbps;
(2) Bus access: The master station is in the token transfer mode, and the master-slave transmission mode between the master station and the slave station is supported, and the single-master or multi-master system is supported. The number of points is 126 (including master and slave). The selection of the number of devices on the bus is based on actual conditions.
(3) Communication: use point-to-point (user data transmission) or broadcast (control command); cyclic master-slave user data transmission and acyclic master-master data transmission. The transmission of user data between DPM1 and related DP slaves is automatically executed by DPM1 according to the determined recursive sequence. When configuring the overall system, the user defines the relationship between the slaves and DPM1 and determines which DP slaves are included in the information The cycle of exchanges, which ones are excluded. The data transmission between DPM1 and DP slave is divided into three stages: parameter setting, configuration configuration, and data exchange. In addition to the master-slave function, PROFIBUS-DP allows data communication between the master and the master.
(4) Operation mode: The PROFIBUS-DP specification includes a detailed description of the system behavior to ensure the interchangeability of the equipment. The system behavior mainly depends on the operating status of DPM1. These statuses are controlled by the local or overall configuration equipment, mainly including The following three states: running, clearing, and stopping.
(5) Synchronization: The control command allows the synchronization of input and output; the synchronization mode makes the output synchronization; the lock mode makes the input synchronization.
(6) Function: Cyclic user data transmission between DP master station and DP slave station; dynamic activation and deactivation of each DP slave station; inspection of DP slave station configuration: powerful diagnostic function, three-level diagnostic information; input or output The DP slave station is given an address through the bus; the DP master station (DPM1) is configured through the bus; the maximum input and output data of each DP slave station is 246 bytes. For more specific functions, please refer to relevant information.
(7) Reliability and protection mechanism: the transmission of all messages is carried out according to the Hamming distance HD=4; the DP slave station has a Watchdog timer; the input and output of the DP slave station are accessed and protected; DP User data transmission monitoring with variable timer on the master station.
(8) Device type: the second type of DP master (DPM2) is a programmable, configurable, and diagnostic device; the first type of DP master (DPM1) is a central programmable controller, such as PLC, PC, etc.; DP Slave stations are drives, valves, etc. with binary values or analog input and output. The selection of equipment type should be based on actual conditions.
2.2 Basic functions of DP-V0
(1) Always find the access method
between each master station for token transmission, master-slave cyclic transmission between master station and slave station, support single master station or multi-master station system, on the bus Up to 126 stations. It can adopt point-to-point user teaching data communication, broadcast mode and cyclic master-slave user data communication.
(2) Cyclic data exchange.
DP-V0 can realize central controller (PLC, PC or process control system) and distributed field, equipment (slave station, such as remote I/O, valve, transmitter and inverter, etc.) Fast cyclic data exchange between the master station sends a request message, and the slave station returns a response message after receiving it. Each slave station can transmit up to 224B of input or output.
(3) Diagnosis function It
can diagnose and quickly locate faults at the station level, module level, and channel level.
(4) Protection function The
DP master station uses a monitoring timer to monitor the communication with the slave station, and an independent monitoring timer is set for each slave station. In the specified monitoring time interval, if the user teaching data transmission is not performed, the monitoring timer will time out and notify the user program to process. The DP slave uses a monitoring timer to check the data transmission between the side and the master. If the data communication is not completed within the set time, the slave automatically switches the output to a fail-safe state.
(5) The configuration function and control function of the
network can realize the following functions through the network: dynamically activate or close the DP slave station, configure the type 1 DP master station, and set the number of stations, the address of the DP slave station, input and output Data format, diagnostic message format, etc., and check the configuration of the DP slave. Control commands can be sent to all slaves at the same time as part of the slaves.
(6) Synchronization and freezing function The
master station can send commands to a slave station or at the same time to a group of slave stations. After receiving the synchronization command from the master station, the slave station enters the synchronization mode, and the output of these slave stations is kept in the current state. In the subsequent user data transmission, the output data is stored in the slave, but its output state remains unchanged. Need to use UNSYNC command to release the synchronization mode. Freeze (FREEZE) command makes the designated slave station group enter the freezing mode, that is, the input data of each slave station is frozen in the current state, and it is not refreshed until the master station sends the next freeze command. Need to use the UNFREEZE command to release the freeze mode.
(7) Cyclic data transmission between a type 1 DP master station and the configuration device
PROFIBUS-DP allows data exchange between a type 1 DP master station and a type 2 DP master station. This function enables configuration and diagnostic equipment to configure the system through the bus, change the operation mode of the type 1 DP master station, and dynamically allow or prohibit the exchange of data between the type 1 DP master station and some slave stations.
2.3 Extended functions of DP-V1
(1) Non-isochronous data exchange
In addition to the functions of DP-V0, the main feature of DP-V1 is the non-isochronous data exchange function between the master station and the slave station, which can be used To carry out parameter setting, diagnosis and alarm processing. It is executed in parallel with cyclic data exchange, but has a lower priority.
(2) The extended diagnosis function
DP slave station transmits the emergency event (alarm information) to the master station through the diagnosis message, and the master station sends a confirmation message to the slave station after receiving it. The slave station can send new alarm information only after it is received, which can prevent repeated sending of the same message multiple times. The status message is sent from the slave station to the master station without the master station's confirmation.
2.3 The main extended functions of DP-V2
(1) The communication between the slave station and the slave station
The direct data exchange (DX) communication between the slave stations adopts the broadcast communication method. As the producer, the slave station can directly pass through the master station. Send the information to the slave station as the consumer. In this way, the slave can directly read the data of other slaves.
(2) Isochronous synchronization mode The
synchronization function can realize the clock synchronization between the master station and the slave station, regardless of the bus load. This function can realize high-precision positioning processing with a clock error of less than 1μs. Through the global control of the broadcast message, all related equipment cycles are synchronized with the bus master cycle.
(3) Clock control and time stamping
Through the new connection MS3 for clock synchronization, the real-time time master station sends the time stamp to all slave stations and synchronizes the clock of the slave station to the system time with an error of less than 1ms. In a network with a large number of master stations, this function can be used to achieve high-precision event tracking and event sequence recording.
3. DP distributed IO expansion;
4. Distributed IO address allocation
1. Profibus-DP and distributed I/O
DP master station is the connection link between the control CPU and distributed I/O. The DP master exchanges data with distributed I/O through PROFIBUS DP and monitors PROFIBUS DP. Distributed I/O (DP slave) is responsible for preparing encoder and actuator data on the spot, so that the data can be sent to the control CPU via PROFIBUS DP.
