This engineering publication provides guidelines for applying circuits complying with TIA/EIA-485-A, referred to as 485 hereafter, to form a balanced multipoint data bus. The versatility of the 485 electrical standard covers a wide variety of data interchange applications all of which this publication cannot cover. The intent is to provide basic design guidelines of the physical layer.

In applying the drivers and receivers defined in 485, the reader should keep several important considerations in mind. The first consideration is the actual configuration of the system with regard to the number of drivers and receivers, the operating speed of the system, the method of interconnecting the equipment, and the system margin. The implementer should consider performance capabilities of the equipment in establishing the margin allotments. The referencing standard should specify these requirements.