Serial Communications Standards
RS232 is the most commonly used, because almost every computer is equiped with one or more serial ports. Because RS232 signals share a common ground, they are sensitive for interference, therefore the distance is limited to 15 meters. RS232 can only be used for point to point connections (one sender, one recipient). For the pin layout of RS232 connectors click here.
RS422 is a high speed digital interface - unlike RS232 which uses signals with reference to ground, RS449 receivers look for the difference between two wires. By twisting the two wires and making a "twisted pair" any noise or interference picked up on one wire will also be picked up on the other, because both wires pick up the same interference the RS449 differential interface just shifts in voltage level with reference to ground, but does not change with respect to each other. The receivers are only looking at the difference in voltage level of each wire to the other not to ground. For the pin layout of RS422 connectors click here.
RS423 is a not commonly used enhanced version of the RS232 standard. The only difference is that it can be used for greater distances. The interface looks like it uses differential signals, but in fact, all B pins are connected to ground. RS423 can be used for point to point or multidrop (one sender, up to 10 recipients) communications. For the pin layout of RS432 connectors click here.
RS449 is a not commonly used enhanced version of the RS232 standard. Another name for RS449 is V.11 Like RS 485 and RS 422 it uses differential signals over twisted pair cables which reduces errors caused by noise or interference. RS449 can be used for point to point or multidrop (one sender, up to 10 recipients) communications. For the pin layout of RS449 connectors click here.
RS485 is the most enhanced RS232 based serial interface available. It can handle high speeds and long cable distances up to 4000 feet. Like RS 449 and RS 422 it uses differential signals over twisted pair cables which reduces errors caused by noise or interference. RS485 uses multipoint technology, it is possible to connect 32 devices on a single RS485 bus. Connection speeds can be as high as 35 Mbs . For the pin layout of RS485 connectors click here.