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Introduction to RS485  HYPERLINK http://www.lammertbies.nl/comm/info/RS-232_specs.html RS232, RS422, RS423 and RS485 are serial communication methods for computers and devices. RS232 is without doubt the best known interface, because this serial interface is implemented on almost all computers available today. But some of the other interfaces are certainly interesting because they can be used in situations where RS232 is not appropriate. We will concentrate on the RS485 interface here. RS232 is an interface to connect one DTE, data terminal equipment to one DCE, data communication equipment at a maximum speed of 20?kbps with a maximum cable length of 50 feet. This was sufficient in the old days where almost all computer equipment were connected using modems, but soon after people started to look for interfaces capable of one or more of the following: Connect DTEs directly without the need of modems Connect several DTEs in a network structure Ability to communicate over longer distances Ability to communicate at faster communication rates RS485 is the most versatile communication standard in the standard series defined by the EIA, as it performs well on all four points. That is why RS485 is currently a widely used communication interface in data acquisition and control applications where multiple nodes communicate with each other. Differential signals with RS485:Longer distances and higher bit rates One of the main problems with RS232 is the lack of immunity for noise on the signal lines. The transmitter and receiver compare the voltages of the data- and handshake lines with one common zero line. Shifts in the ground level can have disastrous effects. Therefore the trigger level of the RS232 interface is set relatively high at ±3?Volt. Noise is easily picked up and limits both the maximum distance and communication speed. With RS485 on the contrary there is no such thing as a common zero as a signal reference. Several volts difference in the ground level o