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Difference Between RS-232 and RS-485

RS-232 vs RS-485

RS-232 and RS-485 are two standards for electrical transmission that predated modern computers. And despite their age, they are still pretty much in use today. The main difference between the two is the number of wires that they use. RS-232 uses 9 distinct wires; although some connectors, like the DB25, have more pins; the extra pins are unused and are just connected to ground. On the other hand the RS-485 only uses 3 wires; 2 for data transmission and 1 for the common ground. The use of fewer wires means that the RS-485 is more cost effective than the RS-232 as there is less expense on the wiring.

One advantage of the RS-232 is that it is already full duplex compliant. RS-485 can only operate at half duplex unless a second set of wires is employed so that one set is used for transmitting and the other is used for receiving.

There is also a difference between the RS-232 and the RS-485 when it comes to the voltages that they use. The RS-485 only uses positive and negative 5V to create a voltage differential which the receiver then recognizes as ones and zeros. On the other hand, the RS-232 recommends transmission voltage ±12V, although the maximum is at ±15V. The voltage level can deteriorate to as low as ±3V at the receiving end and still be understandable to the receiver.

Another advantage of the RS-485 is its excellent range. A single RS-485 link can reach up to 4,000ft. or 1,200m. In comparison, the RS-232 cables have a typical range of 50ft. or 15m. With the use of specialized cables, the range of the RS-232 cables can be extended but only up to 1,000ft. or roughly 300m.

Although both these electrical transmission standards were not intended for the computer industry, they’ve seen some wide use at one point or another. RS-485 was once used with SCSI and RS-232 was a common interface for modems, keyboards, mice, and many other computer peripherals. Nowadays, RS-232 is already obsolete and being phased out in favor of other standards like USB and Firewire. But many computers still have an RS-232 port for compatibility purposes. RS-485 is also being phased out in computer hardware but has enjoyed wide use in other electronic devices; an example of which is in controlling CCTV cameras.

Summary:

1.RS-232 uses 9 wires while RS-485 only uses 3.
2.RS-232 is full duplex while RS-485 is half duplex.
3.RS-232 operates at ±15V while RS-485 only operates at ±5V.
4.RS-485 has a longer range than RS-232.
5.RS-232 is more common in computers than RS-485.


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