Modbus TCP communication protocol is widely utilized in industrial settings, and ABB robots are no exception. This protocol serves as a vital link for seamless data exchange between ABB robots and other devices within an industrial network.
Modbus TCP operates over the TCP/IP network stack. It enables ABB robots to communicate with various components such as programmable logic controllers (PLCs), human – machine interfaces (HMIs), and sensors. One of its key advantages is its simplicity. The protocol uses a client – server model, where the ABB robot can act as either the client or the server. For instance, when the robot is set as a client, it can request data from a server – based PLC, like the status of input/output signals.
In terms of application, ABB robots using Modbus TCP can be integrated into complex manufacturing lines. They can receive real – time commands from a central control system, allowing for precise control of the robot’s movements. For example, in an automotive assembly line, the robot can receive instructions on the type of part to pick and place based on data transmitted via Modbus TCP.
However, like any protocol, there can be challenges. Network latency can sometimes affect the communication speed. To mitigate this, proper network configuration, such as using high – speed Ethernet cables and optimizing network settings, is essential. By leveraging the Modbus TCP communication protocol, ABB robots can enhance their interoperability and contribute to more efficient and integrated industrial automation processes.
- Definition
Modbus communication protocol, the most important one is Modbus RTU (RS-485 bus) to 232 connection ABB COM port,
Modbus ASCII and Modbus TCP (Ethernet) three types.
Modbus RTU protocol, generally speaking, Modbus communication protocol based on serial communication refers to Modbus RTU communication protocol.
Modbus ASCII protocol: The message uses ASCII characters. The ASCII format uses longitudinal redundancy checksum. Modbus ASCII message starts with a colon (“:”) and ends with a line break (CR/LF).
The Modbus TCP protocol adds an MBAP message header to the RTU protocol, and because TCP is a service based on reliable connections, the CRC checksum in the RTU protocol is no longer needed, so there is no CRC checksum in the Modbus TCP protocol, so a more popular saying is often used: the Modbus TCP protocol is the ModbusRTU protocol with five 0s and a 6 in front, and then removes the two CRC checksum bytes.
Communication mode: polling (read 0.1s, write 0.1s) - Function
Modbus TCP uses the TCP protocol to transmit data, and the transmitted data is in Modbus format. When the client transmits data, it sends it in hexadecimal, two bits each time; when the server receives data, it also receives it in hexadecimal form, two bits each time. For example: 0X00, two hexadecimal digits are 8-bit binary numbers.
There are four types of operation objects for Modbus TCP: coils, discrete inputs, holding registers, and input registers.
Object Meaning
Coil PLC output bit, switch quantity, in Modbus
Readable and writable
Discrete quantity PLC input bit, switch quantity, in Modbus
Read only
Input register PLC register that can only be changed from analog input terminal, in Modbus
Retention register PLC register used to output analog signal, in Modbus
Readable and writable
The function codes of Modbus are: (using hexadecimal)
Function code Meaning Function code Meaning
0x01 Read coil 0x04 Read input register
0x05 Write single coil 0x03 Read retention register
0x0F Write multiple coils 0x06 Write single retention register 0x02 Read discrete input 0x10 Write multiple retention registers III. Communication
Communication mode
Modbus TCP devices can be divided into master station (poll) and slave station (slave). There is only one master station and multiple slave stations. The master station sends request frames to each slave station, and the slave station responds. When using TCP communication, the master station is the client and actively establishes a connection; the slave station is the server and waits for the connection.
Master station request: function code + data
Slave station normal response: request function code + response data
Slave station abnormal response: abnormal function code + abnormal code, where the abnormal function code is the highest valid position of the request function code - The abnormal code indicates the error type
Note: A timeout management mechanism is required to avoid indefinite waiting for a response that may not appear
Communication process - connect to establish a TCP connection
- Prepare Modbus message
- Use the send command to send a message
- Wait for a response under the same connection
- Use the recv command to read the message and complete a data exchange
- When the communication task ends, close the TCP connection
ABB robots can achieve efficient data exchange with a variety of industrial equipment and systems through Modbus TCP communication, which is of great significance for realizing automated production, improving production efficiency and ensuring production quality. In addition, the widespread use of Modbus TCP also means that ABB robots can be more easily integrated into more complex industrial automation solutions to meet the changing needs of industrial production.