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Can I Optimize Serial Port Networks?


Last Update: 11/12/2018

In many industrial applications, the best way to access process information is through the device's Serial port. Some devices support the ability to be multi-dropped via RS-422 or RS-485, while others may only support a single point-to-point connection via RS-232. In either case, the application needs to access multiple devices from the PC's single serial port.

Note: KEPServerEX supports Serial COM Port Sharing, where a single COM port can be shared among different Serial devices that take turns communicating over the connection. This functionality is supported by select drivers. To access the shared serial port setting, open the Communications tab located in Channel Properties

Optimizing Serial Connections
Users can configure multiple Serial communication ports using a hardware solution via Edgeport's USB-to-Serial Converters. For otherSerial communications converters, refer to Kepware's Driver List for KEPServerEX. The Edgeport 1, 1i, and 4s USB-to-Serial converters have been tested with the KEPServerEX communications platform.

Users looking to buy a multi-port converter for their application can get direct support on Edgeport products. There is no additional cost in KEPServerEX to use additional serial ports; up to 100 ports are supported. While most applications can benefit from the methods discussed here, each application is unique and may not see the full performance gains described.

For example, take a scenario where users have an application that needs to gather data from four PLCs but there is only one COM port on the PC. It is possible to "round-robin" over the Serial port to get the data from the PLCs one at a time. If a multi-port USB-to-Serial converter is applied, however, the improvement in acquisition cycle time is almost four-fold. In KEPServerEX, each independent COM serial port configured in the server is essentially its own thread of execution. By using four serial ports, KEPServerEX can dedicate a single thread of execution to the task of gathering data from only a single device instead of the round-robin from four devices. To refine the application further, use a multi-port USB-to-Serial Converter.

Take another scenario where the PLCs only support RS-232. Using the standard PC COM port, users would only be able to access two of these PLCs. Users can add more serial ports by using an off-the-shelf PCI card, but that can be time-consuming and sometimes difficult. Depending on the PC, there is typically only one spare interrupt available. The USB-to-Serial converters, however, provide a simple plug-and-play solution. With only one USB port, users can expand the serial ports by 1, 2, 3, 4, and 8 depending on their needs. The benefits of USB-to-Serial converters can also be realized in applications with a serial network of RS-485 devices.