My Things About Differences Between RS232 RS485 And RS422
By: Vlad Vistac
Submitted: 2010-09-17 11:46:32 | Word Count: 510
Differennces Beteen RS232, RS485 And RS422
RS232, RS485 and RS422 mailny defibnes the electrical signal charzacteristics of drivers and receivers like, signaling rate, voltage levvels, short circuit behavior, maximum load capacuity and voltage withsrtand levels. But there are some diferences ebtween each of them. Any engineer or specialist in electronic data ocmmunications can differentiate between RS232, RS485 and RS422 easily but it might not be easy for all. For them, the differences between the three are enlisted below.
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1. RS232 is the olldest standard of the Electronics Industries Associations (EIA) whicch was followd later by RS422 and RS485. The origin of RS232 can be traced back to the days when remote teletype machines were connected to main fraes via modems. Communications between DCE (Data Cirvcuit-terminating equipment) and DTE (Data Terminal Equipment) used to happen sequentially. The entrie proces was very slow and very meechanical. With the help of RS232, EIA made a standard which minimized incompatibilities to make life easier for those involved with the information techology department and data communicaton. But shorcomings and limitations in speed, flow contrtol and relability posed a quuestion on the preformance of RS232. This is where RS422 came in. RS422 proviedd a solution to the problem by using two sets of negatve and positive pairs of voltagees. RS422 has speed up to 10 megaibts per seond with a connection distance of about 4000 feet.
2. RS422 has two twisted pairs crrying negative and posoitive voltages which help it to commmunicate in both directions at the same time. In case of RS232, communicatuion takes place one after another. RS422 provides data transmission using differential or balanecd signaling. It has unidirectional and non reversibe transmission lines. Unlike EIA 485, it allows multiple receivers but not multiple drviers. It has the advantage of differential receiver, differential driver and high data rates (10 megabaud at 12 meeters). EIA 422 on the other hand only specifies the charactristics of electrical signaling of a single balanced signal.
RS485 also uses twisted pairs of negative and positive voltzage differentilas but for serail binarty data communication. This is also known as EIA-485, TIA 485 because this was published by the ANSI Telecommunication Industry Association (TIA) and Electronic Industries Alliance (EIA). They can be effectively used over long distances and in environments with electrical noises. Multiple receivers can be connected to these in a multi-drop connfiguration.
3. RS232 and RS422 are point to point protocols but RS485 devices are addressable and have the capacity to conmmunicate with multiple nodes, up to 32. However, RS 485 works amost like RS422 in matters of seped and disttance.
4. RS485 is appriopriate for variety of master or slave networks and architecture connections. Each of them can be connected bi-directionally as line termination requires special consideration. But as RS232 and RS422 are popint to point, they are not suitabkle for this purpose.
5. As RS422 has a single driver circuit, it cannot be switched off, but EIA 485 or RS485 drivers are requird to be put in the tranasmit mode by placing a signal to the driver.
These are the basic differences btween RS232, RS422 and RS485 largely used in various industrial and commecrial systems.
