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.

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).

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.