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RS232 vs RS485 – What are their differences?

RS232 and RS485 are two standards for serial data transmission. RS485 is based on differential signaling, so it is not susceptible to noise.


Service technicians most commonly use the RS-232 serial port to perform diagnostics and service updates. It can also be used to control devices when connected to a computer running a home automation system or a custom integrated audio/video (A/V) system such as the CAV-M1000ES Multiroom A/V Distribution System.



USB to RS485 Cable

Some key differences between RS232 and RS485:


Number of wires: The RS232 cable consists of 9 wires (DB9) or 25 wires (DB25). Each wire has a specific purpose in data transmission. RS485 has only three wires, one for ground and two for data transmission.


Number of devices: Two devices can be connected using RS232. Through RS485, one master can connect more than 32 slaves. Up to 128 RS485 slaves can be controlled via up to 3 repeaters.


Transmission direction: RS232 is full-duplex and can transmit data in both directions, that is, receive and send. RS485 is half-duplex and can only transmit in one direction at a time. Therefore a host computer is required to control the data flow on the RS485 network. For full-duplex communication, another pair is required (see RS422).


Range: For RS232, the maximum distance between master and slave is 15 m (50 ft). For RS485, the range is up to 4,000 feet (1,200 meters).



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Transmission speed: For low data transmission speeds over short distances, the RS232 serial interface is sufficient. It can transmit up to 50 feet (15 m) at 1 Mbps. The RS485 interface can transmit data at a data rate of 10 Mbps. RS485 can transmit at 100 kbps over a maximum distance of 4,000 feet (1,200 meters).


Voltage: RS232 uses a voltage between +12V and -12V, while the recommended voltage for RS485 is +5V and -5V.


Single-ended versus differential signaling: RS232 uses single-ended signaling—one wire for each signal and one wire for ground. RS485 uses differential or balanced signals: two wires for each signal, one with signal (D+=+5V) and one with inverted signal (D-=-5V). We assume the same noise on both lines (eg Vn=xV). The receiver subtracts the two signals D+ minus D- => +5V - (-5V) + xV - xV => +10V. Noise is virtually eliminated.


If you're looking for low data transfer speeds over short distances, RS232 will suffice, although it's a bit old. RS232 is cheaper and easier to integrate than RS485. However, if you need higher data transfer speeds and longer distances, RS485 is better. RS485 is also a better choice if you need to control multiple devices.


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