Industrial communication utilizes various communication interfaces, necessitating information sharing and data exchange between multiple devices. Commonly used industrial control equipment communication ports include RS-232, RS-485, CAN, and network. Due to the incompatibility of protocols across these communication structures, operation and information exchange between heterogeneous networks are difficult. Multi-protocol converters can be used to network devices with different interfaces, enabling interoperability. Based on multiple communication ports and various protocols, a wide variety of protocol converters have been developed. Major categories include E1/Ethernet protocol converters, RS-232/485/422/CAN converters, and RS-232/485/CAN converters. Let's take a closer look!
E1/Ethernet protocol converter:
Existing E1 and Ethernet-based protocol converters are mainly divided into the E1/Ethernet series and the E1/V.35 series. Using E1 links to transmit Ethernet data has wide applications in practice. Because E1 and Ethernet use different data transmission protocol standards, a protocol converter is needed to perform data conversion. Existing E1/Ethernet protocol converters all operate based on the overall transmission capacity of the E1 link when converting data.
It converts Ethernet or V.35 signals into E1 signals for long-distance transmission over synchronous/quasi-synchronous digital networks. Its primary purpose is to extend the transmission distance of Ethernet and V.35 signals; it is a network access device.
Protocol gateways typically perform protocol conversion between network areas using different protocols. This conversion process can occur at Layer 2, Layer 3, or Layers 2 and 3 of the OSI reference model. However, there are two types of protocol gateways that do not provide conversion functionality: security gateways and pipes. Due to the logical differences between two interconnected network areas, a security gateway is a necessary intermediary between two technically similar network areas, such as a private WAN and the public Internet.
RS-232/485/CAN converter:
Based on the combination of centralized serial ports and different protocols, the main types include RS-232 serial port to 2M converter, RS-485/422 serial port to 2MG.703 converter, RS-232 to 2ME1 converter, CAN to 232/485 converter, USB to RS-232/485/422 converter, etc.
Devices with serial communication capabilities are still widely used in the control and communication fields. However, with the increase in the number of connected devices and the increasing complexity of application functions, the shortcomings of traditional serial communication networks are becoming more and more obvious. By using RS232/CAN intelligent converters to upgrade, modify, or rebuild existing communication or control networks, it is easy to realize multi-point networking and remote communication of RS232 devices. In particular, without changing the original RS232 communication software, users can directly embed it into the original application field, enabling the system design to reach a more advanced level. While significantly improving system functions and performance, it reduces the waste caused by repeated investment and system upgrades.
The primary function of a USB-RS232 interface converter is to convert between the two bus protocols. The host can use the new USB bus protocol to send data, and the converter internally converts the data format to RS232 serial signals before sending it to the device. Data sent back from the device is converted to USB protocol data by the converter.
USB-RS232 interface converters can add special functions when converting the protocol of the data being transmitted.
1. Since the USB bus is much faster than the RS232 interface, a data buffer can be designed on the interface converter to accommodate the speed difference between the two buses.
2. There are some variations of the RS232 interface, such as RS485 and RS422 interfaces. The interface converter can be designed as an RS232-RS485 or RS232-RS422 interface converter to simplify the communication interface conversion of the entire system.
3. When performing data format conversion, the interface converter can be designed with encryption and decryption algorithms to process the data flowing through it, thereby improving the data confidentiality of the system.
Fieldbus-based protocol converter:
Research based on fieldbus has revealed that the competition and coexistence of multiple bus standards objectively cause inconvenience in applications.
The combination of CAN bus and Modbus protocols, by using the Modbus protocol to replace the original custom serial port protocol, categorizes communication tasks into read and write operations, and simplifies the communication process using the standard function codes defined by the Modbus protocol, improving efficiency. It also makes the system open, allowing for easy network formation. The Modbus protocol is a master-slave protocol, while the CAN bus protocol is a multi-master peer-to-peer protocol. This determines that the designed protocol converter acts as a slave station in a Modbus network and as the highest-priority transmitting node in a CAN network.
Modbus and CAN protocol conversion principle: The DSP's RAM is divided into storage buffers for Modbus and CAN messages (each containing its own input and output buffers). The protocol converter receives messages from the Modbus master and stores them in the Modbus receive buffer. When returning a response to the master, it reads data from the CAN bus receive buffer, packages it into a Modbus response message format, and sends it. The protocol converter retrieves messages from the Modbus receive buffer and stores them in the CAN message send buffer. Based on the function code, it analyzes the transmission to determine whether to use a single or multi-transmission method. In short, it's a store-and-forward mechanism. This mechanism prioritizes the reliability of communication conversion; the latency introduced by store-and-forward directly reduces the real-time performance of communication.
