Chances are, your automation application is progressing with Modbus. It is also safe to say that this widely used industrial communication protocol follows a master-slave architecture and will remain the lifeblood of the network for a long time to come. Its two main formats - Modbus RTU and Modbus TCP (a modified version of the former) - function in serial-based communications and Ethernet-based connections, respectively.
There are many reasons for Modbus' status as the de facto industrial communication protocol. Specifically, Modbus RTU is easy to install in field devices. Plus, it's easy to troubleshoot and doesn't cost much. Modbus RTU's cousin, Modbus TCP, is connected for the same reasons as Ethernet. The problem is that they have communication problems, so a mediator is needed to resolve the issues between them. As a result, network engineers are constantly scrambling to find the right solution to ensure that all serial devices can communicate with the SCADA host. This has become a relevant problem as more and more serial devices are connected to Ethernet. UART-модуль
In addition to this issue of incompatibility, the Territory faces other challenges. The first challenge involves the vast amount of proprietary SCADA software on the market. Because each software program brings different support capabilities to Modbus drivers, it is complicated for system operators to match the correct product to their network requirements. Further out of balance is multiple SCADA masters consecutively requesting access to the same Modbus RTU-supported device. In addition to all of the above, operators must ensure that equipment is more responsive in mission-critical applications.
In this paper, we propose solutions to these challenges. Most solutions involve embedding a gateway in the network to ensure you get the most out of your serial devices.
A link to achieve the goal
Currently, the market is crowded with SCADA software offering different functions that support Modbus drivers. Therefore, you need to know in advance which SCADA software is the perfect match for your system. Common in the following scenarios.
1. SCADA host with Modbus TCP driver: A protocol conversion gateway is the most obvious solution here. Gateways allow you to communicate with Modbus RTU-supported devices using the Modbus TCP protocol. When the gateway receives a Modbus TCP request, it converts the packet into a Modbus RTU packet and immediately sends it to the Modbus RTU-capable device.
2. SCADA host with Modbus RTU driver - no built-in serial port: If you want to use existing SCADA programs and equipment, but your original SCADA host does not have a built-in serial port, you can use a serial device server as a remote The serial port on the serial device server builds a virtual COM port to connect to your serial device. This configuration allows you to access a remote serial device through a serial device server as if it had a native COM port. The serial device server will install a virtual COM port driver on the SCADA host to create a virtual COM port. To enable virtual COM ports, the serial device server must be configured in virtual COM mode. Data sent to this virtual COM port will be transferred to the remote serial port of the serial device server. Actions for modem signals will also be handled in the same way. GPRS-модуль
Virtual COM port: Access remote serial devices, just like the SCADA host has a local COM port.
While serial device servers can also connect Modbus RTU devices to Ethernet, a gateway solution can meet almost all system requirements. Your host must be able to support Modbus TCP connections. This shouldn't be a problem since, as mentioned earlier, Modbus TCP is very popular and widely supported. Here are some situations where you need to use a designated gateway solution:
1. Multi-host or Redundancy: In addition to enabling remote access, Ethernet connections provide multiple connection access capabilities. Most gateways can support up to 32 connections, which means that up to 32 SCADA masters can simultaneously query Modbus-RTU-supported devices. While it is difficult for serial device servers to provide network redundancy in this case, since most serial device servers do not support multiple masters, gateways, on the other hand, have no problem.
2. Simultaneous device access for legacy Modbus RTU HMI and new Modbus TCP SCADA systems: While Ethernet connections provide easy-to-deploy remote access, sometimes you may wish to keep an existing local HMI connection active. The problem is that the serial port on the device is connected to the gateway, so there is no serial port available for the HMI connection. In this case, some gateways offer serial port redirectors to overcome this obstacle. A serial port redirector is very similar to a router in that the gateway can transfer requests between different serial ports based on the slave ID.
The serial port redirector keeps the local HMI connection active even when a new Modbus TCP SCADA system is added.
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