Modbus protocols include Modbus ASCII, Modbus RTU, Modbus TCP, etc., and do not specify the physical layer. This protocol defines the message structure that controllers can understand and use regardless of the network over which they communicate.
Modbus Communication Protocol Overview
The standard Modicon controller uses RS232C to implement serial Modbus. The ASCII and RTU protocols of Modbus stipulate the structure of messages, data, commands, and response methods. Data communication adopts the Master/Slave method. The Master sends a data request message, and the Slave can send data to the Master after receiving the correct message. To respond to the request, the Master can also directly send messages to modify the data on the Slave to achieve bidirectional reading and writing.
Modbus has the following characteristics
1. Padrão e aberto. Os utilizadores podem utilizar o protocolo Modbus gratuitamente e com confiança. Não há necessidade de pagar taxas de licença e não infringe os direitos de propriedade intelectual. Atualmente, existem mais de 400 fabricantes que suportam o Modbus e mais de 600 produtos que suportam o Modbus.
2. O Modbus pode suportar uma variedade de interfaces eléctricas, como RS-232, RS-485, etc., e pode também ser transmitido em vários meios, como par entrançado, fibra ótica, sem fios, etc.
3. O formato da estrutura do Modbus é simples, compacto e fácil de compreender. É fácil de utilizar pelos utilizadores e fácil de desenvolver pelos fabricantes.
In fact, Modbus protocols include Modbus ASCII, Modbus RTU, and Modbus TCP
The standard Modicon controller uses RS232 to implement serial Modbus. The ASCII and RTU protocols of Modbus stipulate the structure of messages and data, the command and response methods, and the data communication adopts the Maser/Slave method.
Modbus protocol requires data verification. In addition to parity check, the serial protocol uses LRC verification in ASCII mode and 16-bit CRC verification in RTU mode. Modbus TCP mode does not specify additional verification because the TCP protocol is a reliable connection-oriented protocol.
Difference between Modbus RTU and Modbus TCP protocols
The RTU and TCP protocols are very similar. Just remove the two-byte check code of the RTU protocol, then add 5 0s and a 6 at the beginning of the RTU protocol and send it out through the TCP/IP network protocol.
Modbus RTU and Modbus TCP are both MODBUS protocols in essence, and both rely on MODBUS register addresses to exchange data; but the hardware interfaces used are different. Modbus RTU generally uses the serial port RS232 or RS485, while Modbus TCP generally uses the Ethernet port. There are many protocol converters on the market today that can easily convert these different protocols to each other.
