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What is a Modbus gateway ?
Modbus gateway is to convert one Modbus protocol frame into other protocol frame.
For example, the data of Modbus RTU and Modbus TCP data can be converted to each other; the application development of master request and slave response can also be carried out to improve the efficiency of protocol conversion; The storage gateway replaces the host to initiate active reporting of Modbus requests.
The device is in Modbus gateway mode to ensure the Modbus conversion efficiency to discard non-Modbus data and prevent interference to the serial bus.
Several common Modbus gateways
The Modbus gateway mentioned below refers to Modbus RTU to Modbus TCP, and does not involve the processing of Modbus ASCII data frames. Modbus ASCII only supports transparent transmission.
Simple Protocol Conversion
The most common and common Modbus gateway function, simple protocol conversion is the most efficient Modbus gateway mode for data processing, it just extracts key fields in the data, and then encodes the extracted data with another protocol (Modbus RTUßà Modbus TCP) to send
The multi-host gateway can only work in the TCP server mode, and can process multiple Modbus TCP host requests at the same time. The serial server receives other host requests when one host request is not completed. At this time, the serial server will perform on the RS485 bus. Arbitration output (in layman's terms, it blocks subsequent instructions).
The first thing to understand is that the communication rate of the serial port is much lower than that of the network port. The host usually only processes a few registers when requesting the RTU device. The "storage gateway" is used in this working environment.
In order to solve the problem of slow return of the first command of the "storage" gateway, a configuration gateway can be used. The configuration gateway also adopts the method of obtaining the register content of the RS485 bus slave station by querying the "storage" gateway in advance.
In order to solve the problem of slow return of the first command, the required register list must be configured inside the gateway in advance.
The difference between Modbus RTU and Modbus TCP:
1. Different concepts
MODBUS is a standard industrial control data exchange protocol, which can exchange protocol data through RTU and ASCII
RTU transmits data directly through binary data, while TCP transmits data in the form of TCP code by converting each byte of binary data into a fixed two-digit hexadecimal string, and then concatenating them in sequence. RTU usually uses the most
2. Different communication methods
Ethernet, the corresponding communication mode is MODBUS TCP
Asynchronous serial transmission (various media, such as wired RS-232-/422/485/; optical fiber, wireless, etc.), the corresponding communication mode is MODBUS RTU or MODBUSASCII. High-speed token transmission network, the corresponding communication mode is ModbusPLUS
Modbus RTU Cable
Modbus TCP Cable
USB to RS485 Modbus Interface Cable
MAX-485 TTL to RS-485 conversion Cable