Abstract

RS-485 is a long-standing differential wired communication heavily relied upon in many industrial applications from factory and building automation, motor drives, medical devices, and grid infrastructure to name a few. The standard is prized for its ability to create long distance wired communication networks across multiple communication nodes while maintaining the robustness required for harsh industrial operating environments. With bus lengths up to 1.2 km (approx. 4000ft) cabling quickly becomes one of the costliest aspects of the system, with cabling requiring at minimum two data lines, neutral, and power cables; it becomes quickly apparent that cost saving measures would be beneficial to end users.

TI’s Powerbus is one way to meet this need as it allows power and data to share the same cabling through On-Off Keying (OOK) modulated RS-485. However, Powerbus and Classical RS-485 are not directly compatible so typically they cannot be mixed and matched. This is problematic for some end users that could benefit from Powerbus, but in some of their systems they don’t control the design of every communication node, so they can’t directly implement Powerbus. This application note aims to guide end users how to design one board that can be placed either in Classical RS-485 systems or systems using Powerbus.