RS232 and RS485 are two serial communication standards. Both standards are designed to communicate between different devices, but they are used in different situations because they have different characteristics. In this paper, we will compare these two standards to better understand the differences between them.
1. Introduction
RS232 and RS485 are both serial communication protocols.RS232 is usually used to connect one-to-one devices while RS485 is usually used to connect one-to-many devices.RS232 is usually used for shorter distances while RS485 can be used for communication over longer distances.
2. Data transmission
RS232 can only transmit data in one direction, i.e. it can only send or receive data at one moment. This is because there is only one sending line and one receiving line.
RS485 is a half-duplex communication protocol, which means that it can send and receive data at the same time, and it uses two lines to transmit data, a mesh line A and a mesh line B. These two lines can transmit data, and the data can flow between these two lines.
3. Communication distance
In RS232, the communication distance is short, up to 50 ft. If a longer distance is required, a modem is needed.
In RS485, the communication distance can reach more than 4000 ft. This is due to the fact that it can connect multiple devices and allow data to be forwarded between them, a feature that makes RS485 ideal for large-scale industrial control systems.
4. Signalling
In RS232, a negative level signal 0 has a voltage of -3 to -15V and a normal level 1 has a voltage of +3 to +15V.
In RS485, the information between the transmitter and receiver is transmitted via a balanced differential transmission line. This transmission line plays the role of a circuit ground, so that signals can be transmitted via differential voltages.
5. Cables
In RS232, it is common to use a cable which consists of three main wires, TXD, RXD and ground. The cable can be shielded or unshielded.
In RS485, the cable can be shielded or unshielded.RS485 communication requires two wires A and B to transmit data and also a common ground. The choice of cable depends on the required distance and ambient noise.
6. Data transmission speed
RS232 communication speed is generally 9600bps, while RS485 can reach 10Mbps.
In summary, the advantages and disadvantages of the two communication protocols RS232 and RS485 are.
RS232.
Advantages: Simple and easy to implement, suitable for point-to-point communication, low cost.
Disadvantages: short communication distance, easy to be interfered with, slower communication speed.
RS485.
Advantages: long communication distance, can connect multiple devices, strong anti-interference ability, fast communication speed.
Disadvantages: more complex implementation, higher cost.