rs-485 circuits

Posted on Feb 4, 2014

When a network needs to transfer small blocks of information over long distances, RS-485 is often the interface of choice. The network nodes can be PCs, microcontrollers, or any devices capable of asynchronous serial communications. Compared to Ethernet and other network interfaces, RS-485`s hardware and protocol requirements are simpler and

rs-485 circuits
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cheaper. The RS-485 standard is flexible enough to allow a choice of drivers, receivers, and other components depending on the cable length, data rate, number of nodes, and the need to conserve power. Several vendors offer RS-485 transceivers with various combinations of features. In addition, there are options for methods of terminating and biasing the line and controlling the driver-enable inputs. In this article, I show several circuits for RS-485 networks. Even if you use prebuilt cards or converters, understanding the options will help you choose the right product and configure it to get the best results for your application. But first, a quick look at RS-485. The interface popularly known as RS-485 is an electrical specification for multipoint systems that use balanced lines. RS-485 is similar to RS-422, but RS-422 allows just one driver with multiple receivers, while RS-485 supports multiple drivers and receivers. The specification document, TIA-485-A, defines the electrical characteristics of the line and its drivers and receivers. There are brief suggestions relating to terminations and wiring, but unlike RS-232, there`s no discussion of connector pinouts or software protocols. An RS-485 network can have as many as 32 unit loads, with one unit load equivalent to an input impedance of 12k. By using high-impedance receivers, you can have as many as 256 nodes. An RS-485 link can extend as far as 4000 ft. , and can...

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