Physical structure of the interface
1, RS232 interface.
One of the computer communication interfaces, usually the RS-232 interface with 9 pins (DB-9) or 25 pins (DB-25) of the type of appearance, the general personal computer will have two groups of RS-232 interface, respectively called COM1 and COM2.
2,RS485
RS485 no specific physical shape, according to the actual situation of the project and the interface.
Electronic characteristics of the interface
1, RS232: Transmission level signal interface signal level value is high (signal "1" for "-3V to -15V", signal "0" for the "3 to 15V"), easy to damage the interface circuit chip, but also because of the TTL level (0 ~ '<0.8v', 1 ~ '>2.0V') is not compatible with the level conversion circuit can be connected to the TTL circuit. circuitry. In addition, anti-interference ability is poor.
2, RS485: Transmission of differential signals logic "1" to the voltage difference between the two lines for + (2-6) V said; logic "0" to the voltage difference between the two lines for - (2-6) V said. Interface signal level is lower than RS-232, it is not easy to damage the interface circuit chip, and the level is compatible with the TTL level, it is convenient to connect with the TTL circuit.
Communication distance
1, RS232: RS232 transmission distance is limited, the maximum transmission distance standard value of 15 meters, and can only point-to-point communication, the maximum transmission rate of up to 20kB / s.
2, RS485: RS485 maximum wireless transmission distance of 1200 meters. The maximum transmission rate is 10Mbps, and the maximum communication distance can be reached only under the transmission rate of 100Kb/s.
Using impedance matching, low attenuation of the special cable can reach 1800 meters! More than 1200 meters, you can add repeaters (up to 8), so that the transmission distance is close to 10Km.
can support multi-point communication
RS232: RS232 interface on the bus only allows the connection of a transceiver, can not support the ability to send and receive multiple stations, so only point-to-point communication, does not support multi-point communication.
RS485: RS485 interface on the bus is allowed to connect up to 128 transceivers. That is, with multi-station communication capabilities, so that users can use a single RS485 interface to easily establish a network of devices.
the difference between the communication line
RS232: you can use three-core twisted pair, three-core shielded wire, etc. RS485: you can use two-core twisted pair, two-core shielded wire. In low-speed, short-distance, non-interference occasions can be used ordinary twisted-pair cable, on the contrary, in high-speed, long-wire transmission, it is necessary to use impedance matching (generally 120Q) of the RS485 special cable (STP-120Q (for RS485 & CAN) - 18AWG), and in the interference of harsh environments should be used in armored twisted shielded cable (ASTP-120Q) (for RS485 & CAN) - pair of 18AWG) should be used in harsh environments, while armored twisted shielded cable (ASTP-120Q) should be used in harsh environments.
Supplement: that is, the RS232 transmission distance is only 15 meters so short, then what is the role of it?
In fact, it has a very wide range of applications, can be connected to a variety of devices, such as monitoring, other equipment upgrades or debugging, etc. may need to use it. Function and USB is relatively close, with the USB port is more and more common, there will be more to convert USB to RS-232 or other interfaces of the conversion device. Through the USB interface can be connected to more RS-232 devices, not only to obtain higher transmission speeds, realizing the real plug and play, while solving the USB interface can not be a long-distance transmission shortcomings (USB communication distance within 5 meters).