When serial, wired data transmission is needed over long distances, or at multi-Mbps data rates, or in harsh environments like industrial floors or outdoors between buildings, a single ended transmission standard like RS-232 just is not going to cut it. Enter the RS-485 and RS-422 standards, which are formally known as TIA/EIA485 and 422, or internationally as ISO/IEC 8482 and CCITT V.11 respectively. Their differential signaling format and twisted pair cabling picks up most noise (such as that from motors, lighting, or high current relays), as a common mode signal, which is effectively rejected by the differential receiver. The wide common mode range minimizes the effects of ground potential differences that arise from nodes communicating at long distances. Both standards support distances up to 4,000 feet (or 1,220 m), but only at low data rates of about 100 kbps or less. Above 100 kbps the maximum transmission distance drops by a factor of about ten for each 10x increase in data rate. This is a conservative assumption, but it gets the user in the ballpark if the transceiver’s datasheet does not give any specific guidance. The RS-422 and RS-485 standards do not specify the connector type, cable, nor data protocol. The standards only define the electrical interface requirements such as voltage levels, loads, etc., so designers are free to use any connector for the interface, although DB9 and RJ45 connectors are the most prevalent. The standard does specify a ground connection between nodes, as this helps minimize ground potential differences and also reduces electromagnetic interference (EMI). These differential standards eliminate the need for the negative supply – or charge pumps – that are required for RS-232 compliance. Another major advantage over RS-232 is the elimination of the point-to-point network constraint (that is, one driver talking to only one receiver). RS-422 and RS-485 both allow more flexibility via multi-point and/or multi-drop connections.