What distinguishes Modbus as an open standard?

Modbus is distinguished as an open standard primarily because it is royalty-free. This means that anyone can use the Modbus specification without needing to pay licensing fees or seek permission from a central authority. This open accessibility encourages widespread adoption and interoperability among devices and systems, making it a favored choice in industrial automation and control systems.

The absence of licensing fees facilitates development and integration, allowing manufacturers and developers to implement Modbus in their products freely. This clarity and accessibility of the standard enhance its utility and foster a community of users who can innovate and contribute to its evolution without legal or financial barriers.

In contrast, other characteristics such as requiring licensing or being proprietary would restrict the use and adaptability of the standard, making it less favorable for broad implementation. Additionally, mandating strict compliance is contrary to the nature of open standards, which typically allow for some flexibility in how the protocol is implemented while still adhering to core concepts and functionalities.