The difference between Lysys plc - RS232 interface and RS485 interface

1. The physical structure of the interface

1. RS232 interface:

One of the computer communication interfaces, usually RS-232 interface appears in the form of 9 pins (DB-9) or 25 pins (DB-25), and generally there will be two sets of RS-232 interfaces on personal computers, which are called COM1 and COM2 respectively.

　　2、RS485：

RS485 does not have a specific physical shape, and the interface is adopted according to the actual situation of the project.

Second, the electronic characteristics of the interface

1. RS232: The signal level value of the transmission level signal interface is high (the signal "1" is "-3V to -15V", and the signal "0" is "3 to 15V"), and the chip that is easy to damage the interface circuit is incompatible with the TTL level (0 - "<0.8V", 1 - ">2.0V"), so the level translation circuit needs to be used to connect with the TTL circuit. In addition, the anti-interference ability is poor.

2. RS485: The logic "1" of the transmission differential signal is represented by the voltage difference between the two wires as +(2-6) V; The logic "0" is represented by the voltage difference between the two wires as -(2-6)V. The interface signal level is lower than that of RS-232, so it is not easy to damage the chip of the interface circuit, and the level is compatible with the TTL level, which can be easily connected with the TTL circuit.

3. The length of the communication distance

1. RS232: RS232 transmission distance is limited, the maximum transmission distance standard value is 15 meters, and can only communicate point-to-point, and the maximum transmission rate is 20kB/s.

2. RS485: The maximum wireless transmission distance of RS485 is 1200 meters. The maximum transmission rate is 10Mbps, and the maximum communication distance can be achieved at the transmission rate of 100Kb/s.

Dedicated cables with impedance matching and low attenuation can reach up to 1800 meters! More than 1200 meters, repeaters (up to 8) can be added, so that the transmission distance is close to 10Km.

Fourth, whether it can support multi-point communication

RS232: The RS232 interface only allows 1 transceiver to be connected on the bus, and cannot support multi-station transceiver capability, so it can only communicate point-to-point, and does not support multi-point communication.

RS485: The RS485 interface on the bus is allowed to connect up to 128 transceivers. That is, it has the ability of multi-station communication, so that users can easily establish a device network with a single RS485 interface.

Fifth, the difference of communication lines

RS232: Three-core twisted pair wire, three-core shielded wire, etc. can be used.

RS485: Two-core twisted pair wire, two-core shielded wire, etc. can be used. In the low-speed, short-distance, non-interference occasions can use ordinary twisted pairs, on the contrary, in high-speed, long-line transmission, impedance matching (generally 120Ω) RS485 special cable (STP-120Ω (for RS485 & CAN) pair 18AWG), and in the interference environment should also use armored twisted pair shielded cable (ASTP-120Ω (for RS485 & CAN) pair 18AWG).

Addendum: Even if the RS232 transmission distance is only 15 meters, what is the effect?

In fact, it is very widely used and can be connected to various devices, such as monitoring, other equipment upgrades or debugging. The function is relatively similar to USB, and as USB ports become more common, there will be more conversion devices that convert USB to RS-232 or other interfaces.

More RS-232 devices can be connected through the USB interface, which can not only obtain higher transmission speed and achieve true plug-and-play, but also solve the shortcomings of the USB interface that cannot be transmitted over long distances (USB communication distance is within 5 meters).

The difference between Lysys plc - RS232 interface and RS485 interface

The difference between Lysys plc - RS232 interface and RS485 interface

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