Engineers are painstakingly aware of the high stakes involved when planning the topology of a Modbus-RTU-to-Modbus-TCP network. It is especially in networks that consist of a large number of Modbus serial devices that things can go wrong, such as connectivity errors at field sites. What’s more, nothing is more discouraging than hours of dedicated planning coming undone in the field.
To engineers, spending too much time and effort on planning a Modbus network’s topology and segmenting devices into subgroups is already counter-productive. The most taxing part of the job is the monotony of keying in hundreds of Modbus slave IDs to set up each gateway’s Modbus slave ID routing table, which lists the connections of Modbus devices (Modbus slave IDs) to specific serial ports on a gateway. Thus, it is no surprise that engineers wish for solutions that save valuable time when setting up multiple Modbus gateways.
For engineers, the ideal situation would be just to send out Modbus requests to a Modbus gateway, and the latter would automatically find the correct serial port that connects with the target Modbus device. The development of such solutions is especially relevant now in the era of the Industrial Internet of Things (IIoT) where a large number of serial devices are migrating to Ethernet-based networks.
Managing a large number of Modbus devices
A key challenge of setting up a Modbus technology is determining the number of gateways needed to transmit data between a large number of Modbus devices and the supervisory control and data acquisition (SCADA) systems. Multiport Modbus gateways are more adept than one-port gateways at managing a large number of Modbus devices. For example, one 16-port Modbus gateway can replace 16 one-port Modbus gateways. For applications where space and budgets are issues, using a multiport Modbus gateway is ideal, as more physical space becomes available and less money is spent, only one power cable and one Ethernet cable are required, and fewer devices need to be configured and managed. Furthermore, the large number of IP addresses needed for 16 one-port gateways can be consolidated into a single IP address. For SCADA systems, another benefit is lower connection fees as they are normally charged according to the number of connections to the system.
However, engineers first need to segment all these devices into groups and then connect them to a specific port on the gateway. This why a well-created Modbus slave ID routing table for a gateway’s serial port is so important, but creating this routing table is time-consuming. Two types of routing mechanisms—both very intricate—address the different requirements in Modbus-based networks.