A question that is often in the discussion of RS232, RS422 and RS485 data transmission protocols are the speed and distance limitations of the various protocols. This directly influences the choice of protocol and deserves a discussion.
To reiterate, from an architectural point of view, RS-232 unidirectional or bidirectional point-to-point, where a single channel of communication "half duplex", or uses two independent channels, two channels are used,or communication "full duplex". 232 can also carry the flow control and modem control signals. There are two types of connectors commonly used for serial communication. One nine-pin and one has 25 pins. RS232 signals consist of voltage relative to a common signal ground. A logical zero, also known as "space", can be 5 to 25 volts. This logic, as a "brand" can be anywhere between 5 and minus 25 volts. This type of communication is referred to as "unbalanced".
TheRS-232 standard defines a maximum speed of only 20 kbps (kilobits per second). The low rate, but do not offer a barrier difficult as serial connections are usually much faster (up to 115kbps and higher). Unfortunately it is the nature of the RS232-based communications is interference between adjacent cables. Capacitance and inductance of the wire to limit the speed of serial communication and the duration of the connection that will lead to a more reliable communication. The general rule, aRS232 connection at full speed should not exceed 50 meters. In essence it is a direct correlation between the speed and the distance 232: the higher the speed, the lower the maximum length of cable failures are too high. It is unclear, and regret that the standard RS-232 was not much faster on the twisted pair technology, which is based at the end of 1960 for many decades. This was clearly a case where the standard-makers did not see theimmediate problem, that of connecting terminals to the very slow modems of the time. So why is RS232 still being used even today? Because it's been around for so long, because it's cheap, and because a lot of handheld devices and instruments still use it.
If RS232's limitations are unacceptable, the solution is often using the RS-422 standard that was designed for higher speed (up to 100kbps) and longer distances (up to 4,000 feet). The maximum data rate of RS-422 is up to 10 mbps over short distances, rivaling Ethernet and USB speeds. How can RS-422 be faster and error-free over much longer distances? Primarily because the standard uses a "balanced" signal on twisted pair wires that is far more immune to interference. This is referred to as "differential" data communication. Ground shifts and most noise is easily recognized and rejected by the receiver. Where does RS-485 fit in? It is used in projects that have the same speed requirements that RS422 can deliver, but also have multiple drivers (as opposed to one in a built-in conflict-422).
They are the 4000-meter maximum cable length and 10 Mbps for RS-422 and RS-485 hard drive limit? Not really. Now there are transceivers, which can accommodate up to 10 Mbps over short distances, and fiber optics will significantly extend the functional length of the transmission serial data. Use the correct adapters, converters, transceivers and serial data transmission is far from dead.
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