Each instrument has its own unique communication protocol, commonly including Modbus communication protocol, RS-232 communication protocol, RS-485 communication protocol, HART communication protocol, etc. So, how do these communication protocols work and what are they

What are the advantages and disadvantages? This article will focus on introducing several common communication protocols currently available! Assist instrument personnel in learning.

Communication protocol: also known as communication protocol, refers to an agreement between communication parties on the control of data transmission. The agreement includes provisions on data format, synchronization method, transmission speed, transmission steps, error detection and correction methods, and control character definitions

A regulation that both parties in communication must comply with, also known as link control protocol.

The commonly used instrument communication protocols are:

·Modbus communication protocol

·RS-232 communication protocol

·RS-485 communication protocol

·HART communication protocol.

·MPI communication

·Serial communication

·PROFIBUS communication

·Industrial Ethernet

·ASI Communication

·PPI communication

·Remote wireless communication

·TCP

·UDP

·S7

·profibus

·pofinet

·MPI

·PPI

·Profibus-DP

·Devicenet

·Ethernet

Modbus Communication Protocol 1

The Modbus protocol was originally developed by Modicon, which became part of Schneider Automation at the end of 1979. Nowadays, Modbus is the most popular protocol in the industrial field worldwide. This protocol supports traditional RS-232

RS-422, RS-485, and Ethernet devices.

Due to the fact that the Modbus protocol is completely open and transparent, and the required software and hardware are very simple, it has become a universal industrial standard. Many industrial equipment, including PLCs, DCS， Smart instruments and other devices are using the Modbus protocol

Establish communication standards between them. With it, control devices produced by different manufacturers can be connected to an industrial network for centralized monitoring.

characteristic

Modbus protocol is a universal language applied to electronic controllers. Through this protocol, controllers can communicate with each other and with other devices via a network (such as Ethernet). It has become a universal industrial standard.

This protocol defines a message structure that a controller can recognize and use, regardless of the network over which they communicate.

The Modbus communication protocol is a master-slave asynchronous half duplex communication protocol that uses a master-slave communication structure to enable bidirectional communication between one master station and multiple slave stations. It describes the process of a controller requesting access to other devices and how to respond

How to detect and record errors in response to requests from other devices. It establishes a common format for message domain patterns and content.

The Modbus protocol includes communication methods such as ASCII and RTU, and does not specify a physical layer. This protocol defines the message structure that the controller can recognize and use, regardless of the network through which they communicate. Standard Modicon Control

The device uses RS232C to implement serial Modbus. The ASCII and RTU protocols of Modbus specify the structure of messages and data, commands, and response methods. Data communication adopts a master-slave mode, where the master sends data request messages and the slave receives them

After receiving the correct message, data can be sent to the main station in response to the request; The master station can also directly send messages to modify the data of the slave station, achieving bidirectional reading and writing.

Master/Slave Principle

When communicating on a Modbus network, this protocol determines that each controller needs to know their device address, recognize messages sent by address, and decide what action to take. If a response is required, the controller will generate feedback information and send it out using the Modbus protocol. On other networks, messages containing Modbus protocol are converted into frame or packet structures used on this network. This conversion also extends the methods of solving node addresses, routing paths, and error detection based on specific networks.

When communicating on the network, the Modbus protocol determines that each controller needs to know their device address, recognize messages sent by address, and decide what action to take. If a response is required, the controller will generate a response and send it to the interrogator using the Modbus protocol.

The Modbus protocol requires data verification. In the serial protocol, in addition to parity verification, the ASCII mode uses LRC verification, and the RTU mode uses 16 bit CRC verification. In addition, Modbus adopts a master-slave mode for timed data transmission and reception. In practical use, if a slave station is disconnected (such as a fault or shutdown), the master can diagnose it, and when the fault is repaired, the network can automatically connect again. Therefore, the reliability of Modbus protocol is good.

Modbus and OSI Reference Model

Modbus ASCII Communication Method Modbus ASCII Communication Method

data frame

Broadcast mode (only for write operations)

Non broadcast mode

Modbus RTU Communication Method

RS-232 Communication Protocol 2

RS-232 is a serial physical interface standard developed by the Electronic Industry Association (EIA) in the United States. RS is the abbreviation for "Recommended Standard" in English, and 232 is the usual identification number. RS-232 interface with 9 pins

In the form of (DB-9) or 25 pins (DB-25), there are usually two sets of RS-232 interfaces on personal computers, called COM1 and COM2.

rs-232 interface

The RS-232 standard has two types of signal lines: 25 signal lines and 9 signal lines, including one main channel and one auxiliary channel. In most cases, the main channel is mainly used, and for general duplex communication, only a few signal lines are needed, such as one transmission line, one reception line, and one ground line.

transfer rate
The data transmission rates specified in the RS-232 standard are 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, and 19200 baud rates.

Remote communication connection data terminal
The RS-232 standard was originally developed for remote communication to connect data terminal equipment (DTE) and data communication equipment (DCE). Therefore, the formulation of this standard did not take into account the application requirements of computer systems. But currently it is widely borrowed as a near end connection standard between computers (more precisely, computer interfaces) and terminals or peripherals. Obviously, some provisions of this standard are inconsistent or even contradictory to computer systems. With an understanding of this background, it is not difficult for us to comprehend the areas where the RS-232C standard is incompatible with computers.

Send and Receive
The terms "send" and "receive" mentioned in the RS-232 standard are defined from the perspective of DTE, not DCE. Due to the fact that information is often transmitted between the CPU and I/O devices in computer systems, both of which are DTEs, both parties can send and receive.

Electrical characteristics
EIA-R232 specifies electrical characteristics, logic levels, and various signal line functions.
On TxD and RxD:
Logic 1 (MARK)=-3V~-15V

Logic 0 (SPACE)=+3~+15V

On control lines such as RTS, CTS, DSR, DTR, and DCD:

Signal valid (connected, ON state, positive voltage)=+3V~+15V

Signal invalid (disconnected, OFF state, negative voltage)=-3V~-15V

RS-232 interface definition (25 cores)

1. Frequency shielding ground wire

2. Send data TXD

3. Receive data RXD

4 requests to send RTS

5. Allow sending CTS

6 Data ready DSR

7 Signal Ground SG

8-Carrier Detection DCD

9 send back (+)

10 Undefined

11 Data transmission (-)

12~17 undefined

18 Data reception (+)

19 Undefined

20 data terminals ready for DTR

21 Undefined

22 Ringing RI

23~24 undefined

25 receive return (-)

RS-232 serial communication wiring method (three wire system)
Serial port data transmission can be achieved as long as there are receiving and sending pins: the receiving and sending pins of the same serial port are directly connected by wires, two serial ports are connected, or one serial port is connected to multiple serial ports. The receiving data pin (or wire) is connected to the sending data pin (or wire), crossing each other and corresponding to the signal ground.
9-pin D-type serial port: 2 "RXD", 3 "TXD", 5 "logical ground"..

25 pin serial communication wiring method

Disadvantages of RS-232:

(1) The signal level of the interface is relatively high, which can easily damage the chip of the interface circuit. Additionally, due to incompatibility with TTL levels, a level conversion circuit is required to connect with the TTL circuit.

(2) The transmission rate is low, and in asynchronous transmission, the baud rate is ≤ 20Kbps.

(3) The interface uses a signal line and a signal return line to form a common ground transmission form, which is prone to common mode interference and therefore has weak resistance to noise interference.

(4) The transmission distance is limited, and the standard maximum transmission distance is 50 feet (actual ≤ 15 meters).

 

RS-485 Communication Protocol 3

 

The RS-485 standard is developed on the basis of RS232, adding multi-point and bidirectional communication capabilities, allowing multiple transmitters to be connected to the same bus, while increasing the transmitter's driving capability and conflict protection features, and expanding the bus

Common mode range, later named TIA/EIA-485-A standard.

Electrical characteristics of RS-485:

Logic "1" is represented by the voltage difference between two lines as+(2-6) V; Logic '0' is represented by the voltage difference between two lines as - (2-6) V. The interface signal level has decreased compared to RS-232, making it less likely to damage the chip of the interface circuit, and this level is consistent with TTL

Compatible with voltage levels, it can be easily connected to TTL circuits.

Spread rate:

The maximum data transmission rate of RS-485 is 10Mbps

RS-485 interface:

It adopts a combination of balanced driver and differential receiver, which enhances the ability to resist common mode interference, that is, it has good noise interference resistance.

Baud rate:

1200bps, 2400bps, 4800bps, 9600bps, 19200bps, 38400bps, 125K

Communication interface method:

RS485 interface: asynchronous, half duplex, serial

Data format:

1 start bit, 8 data bits, 1 stop bit, no checksum

1 start bit, 8 data bits, 1 stop bit, odd parity check

1 start bit, 8 data bits, 1 stop bit, even parity check

When connected to the fieldbus adapter PROFIBUS, the default data format is used.

 

 

The maximum transmission distance standard value of RS-485 interface is 4000 feet, which can actually reach 3000 meters (theoretical data, in practical operation, the maximum distance is only about 1200 meters). In addition, RS-232-C interface is only allowed to connect 1 on the bus

A transceiver, i.e. single station capability. The RS-485 interface allows up to 128 transceivers to be connected on the bus. It has the capability of multiple stations, so that users can easily establish a device network using a single RS-485 interface.

 

9-pin interface:

Meaning of RS485 interface signal

3 RXD - receive data

4 RXD+receive data

5 TXD+send data

7 TXD - Sending Data

 

Disadvantages:
In many cases, when connecting RS-485 communication links, simply use a pair of twisted pair cables to connect the "A" and "B" ends of each interface. And ignoring the connection between the signal ground, this connection method can work normally in many situations, but

There is a significant hidden problem of common mode interference: the RS-485 interface uses differential signal transmission, which does not require detecting the signal relative to a reference point. The system only needs to detect the potential difference between the two wires. But people often

Neglecting the fact that transceivers have a certain common mode voltage range, RS-485 transceivers have a common mode voltage range of -7 to+12V. Only when the above conditions are met can the entire network work properly. When the common mode voltage in the network line exceeds this range, it will affect

The stability and reliability of communication may even damage the interface.

HART Protocol 4

HART(HighwayAddressable Remote Transducer)， An open communication protocol for high-speed channels of addressable remote sensors, launched by the American company ROSEMENT in 1985, is used for on-site intelligent instruments and control room equipment

Communication protocol between backup devices. The HART device provides communication with relatively low bandwidth and moderate response time. After more than 10 years of development, HART technology has become very mature abroad and has become the industrial standard for smart instruments worldwide.

The HART protocol uses FSK frequency shift keying signals based on the Bell202 standard, which superimposes an audio digital signal with an amplitude of 0.5mA on a low-frequency 4-20mA analog signal for bidirectional digital communication, with a data transmission rate of 1.2Mbps. Due to FSK signal

The average value of the signal is 0, which does not affect the size of the analog signal transmitted to the control system, ensuring compatibility with existing analog systems. In HART protocol communication, the main variables and control information are transmitted by 4-20mA. If necessary, additional

External measurement, process parameters, equipment configuration, calibration, and diagnostic information are accessed through the HART protocol.

Basic information of the agreement

·4~20mA analog signal+digital control signal (FSK technology)

·Supports twisted pair full digital communication and can form a network of 15 stations

·Support OSI open architecture, layers 1, 2, 7, and

Communication model:

Physical layer:

FSK technology based on Bell 202 communication standard, basic content:

Baud rate 1200bps (slower speed)

Logic 1 1200HZ

Logic 0 2400HZ

data link layer

Communication method:

1) Master-slave communication

Control the transmission of data frames by the main device

Up to 15 slave devices are allowed to connect to a multi-point communication line

2) Sudden Mode

Repeating data frames from the device at regular intervals

3) Half duplex communication method

Addressing range: 0~15

When the address is 0, it is in a compatible state with 4-20mADC and digital communication.

When the address is between 1 and 15, it is in a fully digital communication state.

Specify the structure of communication data, with each character consisting of 11 bits:

1-bit start bit+8-bit data+1-bit parity bit+1-bit stop bit

Application layer:

General command:

·The command applicable to all field devices that comply with the HART protocol. Including the following content:

·Read the range, unit, and damping time constant of the transmitter;

·Read the number of sensors connected in series and their wiring system;

·Read out the manufacturer and product model;

·Read out the main variables and units;

·Read the output and percentage output of the current;

·Read and write 8-character tag numbers, 16 character descriptions, dates, etc;

General commands are applicable to most products that comply with the HART protocol, but there may be slight differences among HART products from different companies, such as writing the unit of the main variable, fine-tuning the zero point and gain of DA, etc

·Write damping time constant;

·Write the transmitter range;

·Calibration (setting zero and range);

·Fine tune the zero point of the main variable;

·Fine tune the zero point and gain of the DAC;

·Complete self check and host reset;

Special command:

Only applicable to a specific on-site device. This is a unique command for each company's product, which is not compatible with each other, such as characterization, fine-tuning sensor head calibration, etc

·Read or write the square root small traffic truncation value;

·Start, stop, or clear the accumulator;

·Select the main variable (mass flow rate or density);

·Read or write configuration information data;

·Fine tune the calibration of sensors;

HART communication mode:

The first type of "question and answer style": 2 times/second, suitable for point-to-point, multi site connections

The second "group mode": 3.7 times/second, only applicable to point-to-point connections

Advantages of HART protocol:

·Analog signals carry process control information, while digital signals allow for bidirectional communication;

·(Intelligent on-site instruments+analog instruments, recorders, and controllers) hybrid system;

·Support multi master station digital communication, save wires, and reduce installation costs;

·By renting telephone lines to connect instruments, remote on-site instruments can use relatively inexpensive interface devices;

·Allow "question and answer" and "group mode" communication methods;

·The message structure is flexible, standardized, and can carry four process variables in one communication.

There are usually three ways to apply HART communication:

·The most common method is to communicate with on-site intelligent instruments using handheld communication terminals (HHT).

·Control room instruments with HART communication function can communicate and configure with multiple HART instruments.

·The third method is to communicate with a PC or DCS operation station.

The interconnection between the smart transmitter and the HART protocol communicator requires the sum of load resistance to be between 250 and 600 Ω. If it is too small, communication cannot be achieved, and if it is too large, the transmitter cannot function. In practice, it is generally necessary to connect at least one in series in the verification room

A standard resistance of 250 Ω or above, but if the system basically meets the load resistance requirements on site, a HART communicator can be directly connected across the wiring terminals in the control room. As shown in Figure 1

Due to the compatibility between HART instruments and the original 4-20mA standard instruments, the development and application of HART instruments have developed rapidly, especially in equipment modification. Compared with protocols such as FF, the HART protocol is relatively simple, and due to its speed

The requirements for slow and low power consumption are generally implemented by software for the data link layer and application layer. The physical layer uses the existing Bell-202 modem. To address the issue of interchangeability and interoperability between devices from different manufacturers, HART adopts device description

Language (DDL).

MPI Communication Protocol 5

The MPI protocol, whose full English name is Multi point Interface. Can be configured as master/master protocol or master/slave protocol between PLCs. How to operate depends on the device type: If the control station is all S7-300/400 series PLC, then build

Establish a master/master connection relationship, as the MPI protocol supports multi master communication, all S7-300 CPUs can be configured as network master stations, and data exchange between PLCs can be achieved through the master/master protocol. If some control stations are S7-200 series

PLC， Then a master/slave connection relationship can be established, because the S7-200 CPU is a slave station, and users can perform data read and write operations from the S7-300 CPU to the S7200 CPU through network instructions.

PROFIBUS communication protocol 6

PROFIBUS， It is an international, open, and device manufacturer independent fieldbus standard. The transmission speed of PROFIBUS can be selected within the range of 9.6kbaud~12Mbaud, and when the bus system is started, all connections to the bus are available

The device should be set to the same speed. Widely applicable to manufacturing automation, process industry automation, and automation in other fields such as buildings, transportation, and power. PROFIBUS is a device used for factory automation, workshop level monitoring, and on-site equipment layering

According to fieldbus technology for communication and control. Distributed digital control and on-site communication network that can achieve monitoring from the on-site equipment layer to the workshop level provide a feasible solution for achieving comprehensive factory automation and intelligent on-site equipment.

The PROFIBUS protocol structure is based on the ISO7498 international standard, with the Open System Interconnection OSI as the reference model. This model has seven layers in total. （1）PROFIBUS－DP： calm

Defined the first, second, and user interfaces. The third to seventh floors are not described. The user interface specifies the application functions that can be called by users, systems, and different devices, and details the device behavior of various PROFIBUS-DP devices.

（2）PROFIBUS－FMS： The first, second, and seventh layers are defined, and the application layer includes the Fieldbus Message Specification (FMS) and the Lower Layer Interface (LLI).

FMS includes application protocols and provides users with a wide range of powerful communication services to choose from. LLI coordinates different communication relationships and provides a device independent second layer access interface. (3) PROFIBUS-PA: Data Transmission of PA

Adopting the extended PROFIBUS-DP protocol. In addition, PA also describes the PA code of conduct for on-site equipment behavior. According to the IEC1158-2 standard, PA's transmission technology ensures its inherent safety and can supply power to field devices through a bus.

Connectors can be used to expand PA networks on DP. Note: The first layer is the physical layer, the second layer is the data link layer, the third to sixth layers are unused, and the seventh layer is the application layer.

TCP/UDP Protocol 7

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are transport layer protocols. TCP provides reliable data transmission in IP environments, and its services include data streaming, reliability

Effective flow control, full duplex operation, and multiplexing. Send data packets through connection oriented, end-to-end, and reliable methods. Simply put, it opens up a pre connected channel for the data to be sent, and then sends the data; However, UDP does not

Provide reliability, flow control, or error recovery functions for IP. Generally speaking, TCP corresponds to applications with high reliability requirements, while UDP corresponds to applications with low reliability requirements and economical transmission. The main application protocols supported by TCP are:

Telnet, FTP, SMTP, etc; The application layer protocols supported by UDP mainly include NFS (Network File System), SNMP (Simple Network Management Protocol), DNS (Domain Name System), TFTP (Universal File Transfer Protocol), etc.

TCP：

TCP is a connection oriented communication protocol that establishes a connection through a three-way handshake. When communication is complete, the connection must be disconnected. As TCP is connection oriented, it can only be used for end-to-end communication.

TCP provides a reliable data stream service, using the "acknowledgment with retransmission" technique to achieve transmission reliability. TCP also uses a method called "sliding window" for traffic control, where the window actually represents the receiving capability,

Used to limit the sending speed of the sender.

If there are already sealed TCP packets in the IP packet, the IP will forward them 'up' to the TCP layer. TCP sorts packets and performs error checking, while also establishing connections between virtual circuits. TCP packets include sequence numbers and acknowledgements, so

Packages that are not received in order can be sorted, while damaged packets can be retransmitted.

TCP sends its information to higher-level applications, such as Telnet's service and client programs. The application takes turns sending information back to the TCP layer, which then passes it down to the IP layer, device drivers, and physical media, and finally

To the recipient.

Connection oriented services such as Telnet, FTP, rlogin, X Windows, and SMTP require high reliability, so they use TCP. DNS uses TCP (to send and receive domain name databases) in some cases, but it

Transmit information about a single host using UDP.

UDP：

UDP is a connectionless communication protocol, where UDP data includes destination port number and source port number information. As communication does not require a connection, broadcast transmission can be achieved.

UDP communication does not require confirmation from the receiver and is considered an unreliable transmission, which may result in packet loss. In practical applications, programmers are required to program verification.

UDP and TCP are on the same layer, but they do not care about the order, errors, or retransmission of data packets. Therefore, UDP is not applied to connection oriented services that use virtual circuits. UDP is mainly used for query response oriented services, such as

NFS。 Compared to FTP or Telnet, these services require a smaller amount of information to be exchanged. The services that use UDP include NTP (Network Time Protocol) and DNS (DNS also uses TCP).

Deceiving UDP packets is easier than deceiving TCP packets because UDP does not establish an initial connection (also known as a handshake) (because there is no virtual circuit between two systems), which means that services related to UDP face greater risks.

 

Data format:

Data frame: frame header+IP packet+frame tail (the frame header includes the initial MAC addresses and types of the source and destination hosts, and the frame tail is the checksum)

IP packet: IP header+TCP data information (IP header includes source and destination host IP addresses, types, lifetime, etc.)

TCP data information: TCP header+actual data (TCP header includes source and destination host port numbers, sequence numbers, acknowledgment numbers, checksum, etc.)

UDP (User Data Protocol) is a protocol corresponding to TCP. It is a non connection oriented protocol that does not establish a connection with the other party, but directly sends data packets over!

PPI Communication Protocol 8

It is a communication protocol developed by Siemens specifically for the S7-200 series PLC. Built into S7-200 CPU. The PPI protocol is physically based on the RS-485 port, and PPI communication can be achieved by shielding twisted pair cables. PPI protocol is a master-slave protocol. host

The station device sends a request to the slave device, and the slave device responds, but the slave cannot actively send out information. The master station communicates with the slave station through a shared connection managed by the PPI protocol. The PPI protocol does not limit the number of master stations that can communicate with any slave station, but

In a network, there cannot be more than 32 main stations. The most basic purpose of the PPI protocol is to enable Siemens STEP7 Micro/WIN programming software to upload and download programs and communicate with the Siemens human-machine interface and PC.

Pofinet Communication Protocol 9

PROFINET, launched by PROFIBUS International (PI), is a new generation of automation bus standard based on industrial Ethernet technology.

PROFINET, launched by PROFIBUS International (PI), is a new generation of automation bus standard based on industrial Ethernet technology. As a strategic technological innovation, PROFINET provides automation solutions

The information field provides a complete network solution that covers current hot topics in the automation field such as real-time Ethernet, motion control, distributed automation, fault safety, and network security. As a cross vendor technology

The technology is fully compatible with industrial Ethernet and existing fieldbus (such as PROFIBUS) technologies, protecting existing investments.

PROFINET is a complete solution suitable for different needs, which includes 8 main modules: real-time communication, distributed field devices, motion control, distributed automation, network installation, IT standards and information security, etc

Obstacles to safety and process automation.

Distributed field devices:

By integrating the PROFINET interface, distributed field devices can be directly connected to PROFINET.

For existing fieldbus communication systems, transparent connection with PROFINET can be achieved through a proxy server. For example, a PROFIBUS can be accessed through IE/PB Link (a proxy server between PROFINET and PROFIBUS)

The transparent integration of the network into PROFINET, and the various rich device diagnostic functions of PROFIBUS are also applicable to PROFINET. For other types of fieldbuses, a proxy server can be used in the same way to manage the field

Connect the bus network to PROFINET.

Motion control:

Through the synchronous real-time (IRT) function of PROFINET, it is easy to control the servo motion control system.

In PROFINET synchronous real-time communication, each communication cycle is divided into two different parts, one is a cyclic and deterministic part, called the real-time channel; The other one is the standard channel, through which standard TCP/IP data is transmitted

Losing.

In the real-time channel, a fixed cyclic interval time window is reserved for real-time data, and real-time data is always inserted in a fixed order. Therefore, real-time data is transmitted at fixed intervals, and the remaining time in the cyclic period is used to transmit standard data

TCP/IP data. Two different types of data can be transmitted simultaneously on PROFINET without interfering with each other. Ensure reliable control of the servo motion system through independent real-time data channels.

Network installation:

PROFINET supports topologies other than star, bus, and ring. In order to reduce wiring costs and ensure high availability and flexibility, PROFINET provides a wide range of tools to help users easily install PROFINET.

Specially designed industrial cables and durable connectors meet EMC and temperature requirements, and are standardized within the PROFINET framework to ensure compatibility between devices from different manufacturers.

According to different response times, PROFINET supports the following three communication methods.

TCP/IP standard communication

PROFINET is based on industrial Ethernet technology, using TCP/IP and IT standards. TCP/IP is the de facto standard for communication protocols in the IT field, although its response time is approximately on the order of 100 ms. However, for factory control level applications

In other words, this response time is sufficient.

Real time (RT) communication

For data exchange between sensors and actuator devices, the system has stricter requirements for response time, requiring approximately 5-10ms of response time. At present, fieldbus technology such as PROFIBUS can be used to achieve this response time

DP。

For industrial Ethernet technology based on TCP/IP, using a standard communication stack to process process process packets requires considerable time. Therefore, PROFINET provides an optimized, Layer 2 based real-time Ethernet solution

The communication channel greatly reduces the processing time of data in the communication stack through this real-time channel, thus PROFINET achieves real-time performance equivalent to, or even exceeding, traditional fieldbus systems.

Synchronized Real Time (IRT) Communication

In on-site communication, Motion Control has the highest requirement for real-time communication, and PROFINET's Isochronous Real Time (IRT) technology can meet the high-speed communication needs of motion control,

Under 100 nodes, the response time should be less than 1ms and the jitter error should be less than 1 μ s to ensure timely and definite response.

DEVICENET Communication Protocol 10

Devicenet is an open, low-cost, high-performance communication network based on CAN (Controller Area Network) technology that developed in the mid-1990s and meets global industrial standards. It was originally developed by Rockwell Corporation in the United States

Apply.

Devicenet is a low-cost communication bus. It integrates industrial equipment such as limit switches, photoelectric sensors, valve groups, motor starters, process sensors, barcode readers, variable frequency drives, panel displays, and operator interfaces

Connecting to the network eliminates the expensive cost of hard wiring. Direct interconnectivity improves communication between devices and provides significant device level diagnostic capabilities, which are difficult to achieve through hard wired I/O interfaces.

Advantages of Devicenet:

1. Improve the flexibility of design

·Provide unlimited IO ports through the ability to provide network data flow

·Provide interoperability and plug and play capabilities

2. Improved process data management

·Provide peer-to-peer or master/slave management

·As a result of a fast response processing element, throughput and repeatability have been improved

·Implicit diagnostic information included in the position scale and pre event and alarm notifications

·Extend the interval of regular maintenance in diagnosis

3. Reduce installation costs

·Simplify wiring, avoid potential error points, reduce required files, decrease labor resources, and save installation space

The Devicenet protocol is a simple, inexpensive, and efficient protocol suitable for the lowest level fieldbus, such as process sensors, actuators, valve groups, motor starters, barcode readers, variable frequency drives, panel displays, etc

The network of operator interfaces and other control units. Devices that can be connected through DeviceNet include various semiconductor products ranging from simple light barriers to complex vacuum pumps. DeviceNet is also a serial communication link that can reduce expensive hardware costs

Wiring. The direct interconnectivity provided by DeviceNet not only improves communication between devices, but also provides significant device level diagnostic functionality, which is difficult to achieve through hard wired I/O interfaces. In addition to providing Layer 7 of the OSI model

In addition to the definition of the application layer, the DeviceNet specification also defines some layers 1 (physical transceivers) and 0 (transmission media). The figure shows the correlation layers of DeviceNet in the ISO model. We also made physical connections to DeviceNet nodes

Clear regulations. Detailed regulations have been made for connectors, cable types and lengths, as well as indicators, switches, and indoor nameplates related to communication.

Ethernet Communication Protocol 11

Ethernet refers to the baseband LAN specification created by Xerox and jointly developed by Xerox, Intel, and DEC, and is the most commonly used communication protocol standard for existing LANs today. The Ethernet network uses CSMA/CD (Carrier Sense Multiple Access and Collision Detection) technology and operates at a rate of 10M/S on various types of cables. Ethernet is similar to the IEEE802.3 series of standards.

The working principle of Ethernet:

Ethernet adopts the Carrier Frame Listening Multiple Access (CSMA/CD) mechanism with collision detection. In Ethernet, all nodes can see all the information sent in the network, so we say Ethernet is a broadcast network.

The working process of Ethernet is as follows:

When a host in Ethernet needs to transmit data, it will follow the following steps:

1. Monitor whether there is a signal being transmitted on the channel. If there is, it indicates that the channel is busy and continues to listen until the channel is idle.

2. If no signal is detected, transmit data

3. Continue monitoring during transmission. If a conflict is detected, execute the backoff algorithm and wait randomly for a period of time before re executing step 1 (when a conflict occurs, the computer involved in the conflict will send a message and return to the monitoring channel state).

Note: Each computer is only allowed to send one packet and one congestion sequence at a time to warn all nodes

4. If no conflict is found, the transmission is successful. All computers must wait for 9.6 microseconds (running at 10Mbps) after the last transmission before attempting to send data again.