![]() ![]() RS-485 uses two signal lines, ‘A’ and ‘B’, which must be balanced and differential. It handles the conversion of electrical signals into digital data, while defining voltages, timing, data rates, etc. ![]() The physical layer of the OSI model is responsible for the transfer of raw data between a device and a physical transmission medium. Figure 1: Open Systems Interconnection (OSI) model Physical Layer of the OSI Model The Open Systems Interconnection (OSI) model attempts to characterize the various layers of a communication system from final application, down through the electrical layers, and lastly onto the physical layer, Figure 1. RS-485, also known as TIA-485 or EIA-485, is the standard that defines the electrical characteristics of the drivers and receivers for the communication protocol. The ability to use RS-485 at high speeds, over long cabling lengths, in electrically noisy environments, and with multiple devices on the same bus, makes it a smart implementation for most applications requiring a serial interface. Engineers are not only using it for long cabling distances, but are implementing it into applications, such as the automotive industry, where it is uncertain what noise could be encountered in the end application. In addition, the noise immunity offered by the RS-485 standard makes the interface very versatile. RS-485 can also be found in theater applications where many devices are spread out across a huge space. ![]() With the standard allowing for multi-drop (multiple devices on the same bus) and long cabling lengths, it is easy to understand its frequent use in the industrial and automation spaces. RS-485 has been used in a wide range of computer automation systems dating back to when the standard was created in 1998. The RS-485 standard allows for long cabling distances in electrically noisy environments and can support multiple devices on the same bus. RS-485 is an industrial specification that defines the electrical interface and physical layer for point-to-point communication of electrical devices. Fitting the bill for both high speed and industrial robustness, the RS-485 serial interface has become a widely implemented interface for rotary encoders and other motion control equipment. And for applications in the industrial space, not all serial interfaces are created equal. As my favorite engineering professor would always say, “The wonderful thing about standards is that there are so many of them to choose from.” Encoders today are smarter and more advanced than ever before requiring engineers to abandon simpler quadrature incremental sensors and adopt high speed absolute encoders with serial interfaces. With a world of serial interfaces available, it can be hard to understand their differences and when to use each one. ![]()
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