What Are the Speed and Distance Limits of Serial Communication?
One question that often comes up during discussions of the RS232, RS422 and RS485 serial data communication protocols are the speed and distance limits of the various protocols. This directly impacts the choice of protocol and therefore warrants discussion. To reiterate, from an architectural standpoint, RS-232 is a uni-directional or bi-directional point-to-point link where a single channel is used for “half-duplex” communication or two independent channels are used for two way, or “full-duplex,” communication. RS232 can also carry flow control and modem control signals. There are two types of connectors commonly used for serial communication. One has nine pins and one has 25 pins. RS232 signals consist of voltage relative to a common signal ground. A logic zero, also called “space,” can be anywhere from 5 to 25 Volts. A logic one, also called “mark,” can be anywhere between negative 5 and 25 Volts. This kind of communication is referred to as “unbalanced.” The RS-232 standard defines
