The modbus protocol is not the same thing as RS232 or RS485.
Modbus is a communication protocol, while RS232, RS485 can only represent the physical media layer and link layer of communication. modbus protocol supports traditional RS-232, RS-422, RS-485 and Ethernet devices. Many industrial devices, including PLCs, DCSs, smart meters, etc. are using the Modbus protocol as the communication standard between them.
The difference between the three is as follows:
1, Modbus protocol ：
In order to better popularize and promote the distributed application of Modbus on Ethernet-based, at present, Schneider has handed over the ownership of Modbus protocol to IDA (Interface
for
). DistributedAutomation, Distributed Automation Interface) organization, and established the Modbus-IDA organization, laying the foundation for the future development of Modbus. In China, Modbus has become the national standard GB/T19582-2008. according to incomplete statistics: as of 2007, the number of Modbus nodes installed has exceeded 10 million.?
The Modbus protocol is a universal language applied to electronic controllers. The protocol allows controllers to communicate with each other and with other devices over a network (e.g. Ethernet). It has become a common industrial standard. With it, control devices from different manufacturers can be connected into an industrial network for centralized monitoring and control. This protocol defines a message structure that a controller can recognize and use regardless of the network over which they are communicating. It describes the process by which a controller requests access to other devices, how it responds to requests from other devices, and how it detects and logs errors. It establishes a public **** format for the message domain pattern and content.?
When communicating on a Modbus network, this protocol dictates that each controller needs to know the address of their device, recognize messages sent by address, and decide what action to generate. If a response is required, the controller generates a feedback message and sends it out using the Modbus protocol. On other networks, messages containing the Modbus protocol are converted to the frame or packet structure used on that network. This conversion also extends the method of resolving section addresses, routing paths, and error detection based on specific networks.?
This protocol supports legacy RS-232, RS-422, RS-485, and Ethernet devices. Many industrial devices, including PLCs, DCSs, smart meters, etc. are using the Modbus protocol as a standard for communication between them.?
2. RS-232:
The RS-232 interface conforms to the interface standard for serial data communication developed by the Electronic Industries Alliance (EIA) of the U.S.A. The full name of the original number is EIA-RS-232 (abbreviated as 232, RS232). It is widely used for computer serial interface peripheral connections. Connecting cables and mechanical and electrical characteristics, signaling functions and transmission processes.?
3, RS485 :
Intelligent instrumentation is developed with the maturity of microcontroller technology in the early 80's, and now the world instrumentation market is basically monopolized by intelligent instrumentation. The reason for this is the need for enterprise information technology, enterprises in the instrumentation selection, one of the necessary conditions is to have a network communication interface. Initially, the data is a simple analog signal output process, and then the instrument interface is the RS232 interface, this interface can be realized point to point communication, but this way can not realize the networking function. Subsequently appeared RS485 to solve this problem.
Extended information:
Modbus is a serial communications protocol that was developed by Published in 1979 by Modicon (now Schneider Electric) for communication using programmable logic controllers (PLCs), Modbus has become the industry standard (De facto) for communication protocols in the industrial sector and is now a commonly used method of connecting industrial electronic devices.
Versions of the Modbus protocol exist for serial ports, Ethernet, and other networks that support the Internet Protocol.
Most Modbus devices communicate over the serial EIA-485 physical layer.
For serial connections, two variants exist that differ slightly in terms of different numerical data representations and protocol details; Modbus RTU, a compact, binary representation of data, and Modbus ASCII, a human-readable, verbose representation. Both variants use serial communication.
The RTU format follows up with commands/data with cyclic redundancy checksums, while the ASCII format uses longitudinal redundancy checksums. Nodes configured for the RTU variant will not communicate with nodes set to the ASCII variant and vice versa.
For connections over TCP/IP (e.g. Ethernet) where multiple Modbus/TCP variants exist, this approach does not require a checksum calculation.
For all three communication protocols the data model and function calls are the same, only the encapsulation is different.
Modbus has an extended version, Modbus Plus (Modbus+ or MB+), but this protocol is proprietary to Modicon and is different from Modbus. It requires a specialized coprocessor to handle the high speed token rotation similar to HDLC. It uses 1Mbit/s twisted-pair cable and has conversion isolation at each node, a device that uses conversion/edge triggering rather than voltage/level triggering.
Connecting Modbus Plus to a computer requires a special interface, usually a board that supports the ISA (SA85), PCI or PCMCIA bus.
Baidu Encyclopedia: Modbus Communication Protocol