The difference between RS232 ports and RS485 ports
Physical structure of the ports
1. RS232 ports
One of the computer communication interfaces, usually the RS-232 interface appears in the form of 9 pins (DB-9) or 25 pins (DB-25). Generally, there are two sets of RS-232 interfaces on a personal computer. They are called COM1 and COM2, respectively.
2. RS485 ports
RS485 has no specific physical shape, and the interface is adopted according to the actual situation of the project.
Electrical Characteristics of the Interface
1. RS232: The signal level value of the transmission level signal interface is relatively high (signal "1" is "-3V to -15V", signal "0" is "3 to 15V"), which is easy to damage the chip of the interface circuit, and Because it is not compatible with TTL level (0~“<0.8v”, 1~”>2.0V”), it is necessary to use a level conversion circuit to connect with TTL circuit. In addition, the anti-interference ability is poor.
2. RS485: Transmission differential signal logic "1" is represented by the voltage difference between the two lines as +(2-6)V; logic "0" is represented by the voltage difference between the two lines 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 to the TTL circuit.
Communication distance
1. RS232: RS232 has a limited transmission distance, the standard maximum transmission distance is 15 meters, and can only communicate point-to-point, with a maximum transmission rate of 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 only at the transmission rate of 100Kb/S.
Using special cables with impedance matching and low attenuation can reach 1800 meters! More than 1200 meters, can add repeaters (up to 8), so the transmission distance is close to 10Km.
If Can support multipoint communication
RS232: The RS232 interface only allows one transceiver to be connected to the bus, and cannot support multi-station transceiver capability, so it can only communicate point-to-point, not multi-point communication.
RS485: The RS485 interface allows up to 128 transceivers to be connected on the bus. That is, it has multi-station communication capability, so that users can easily establish a device network using a single RS485 interface
Differences in communication lines
RS232: Three-core twisted pair, three-core shielded cable, etc. can be used.
RS485: Two-core twisted pair, two-core shielded cable, etc. can be used. In low-speed, short-distance, and non-interference occasions, ordinary twisted-pair cables can be used. On the contrary, in high-speed and long-term transmission, a special RS485 cable (STP-120Ω (for RS485 & CAN) a pair of 18AWG), and armored twisted pair shielded cables (ASTP-120Ω (for RS485 & CAN) a pair of 18AWG) should be used in harsh environments
Supplement:
Since the RS232 transmission distance is only as short as 15 meters, what does it do? In fact, its application is very extensive, and it can be connected to various devices, such as monitoring, other equipment upgrades or debugging, etc. may need to use it. The function is close to USB. As USB ports become more and 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 not only achieves higher transmission speed, but also achieves true plug-and-play, and solves the disadvantage that the USB interface cannot transmit long-distance (USB communication distance is within 5 meters).
RS232 Features:
RS232 is the serial port, the 9-pin socket at the back of the computer case
Since the RS-232 interface standard appeared earlier, it is inevitable that there are shortcomings, mainly in the following four points:
(1) The signal level of the interface is high, which is easy to damage the chip of the interface circuit, and because it is incompatible with the TTL level, a level conversion circuit is required to connect with the TTL circuit.
(2) The transmission rate is low, in the asynchronous transmission, the baud rate is 20Kbps.
(3) The interface uses a signal line and a signal return line to form a common ground transmission form. This common ground transmission is prone to common mode interference, so the anti-noise interference is weak.
(4) The transmission distance is limited, the standard value of the maximum transmission distance is 50 feet, but it can only be used in about 50 meters in fact.
RS-485 Features:
In view of the shortcomings of RS-232, some new interface standards have emerged, and RS-485 is one of them. It has the following characteristics:
1. Electrical characteristics of RS-485: logic "1" is represented by the voltage difference between the two lines as +(2-6) V; logic "0" is represented by the voltage difference between the two lines as -(2-6) V . The interface signal level is lower than that of RS-232-C, 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.
2. The maximum data transmission rate of RS-485 is 10Mbps
3. The RS-485 interface adopts a combination of a balanced driver and a differential receiver, and the anti-common mode interference ability is enhanced, that is, the anti-noise interference is good.
4. The standard value of the maximum transmission distance of the RS-485 interface is 4000 feet, which can actually be up to 3000 meters. In addition, the RS-232-C interface only allows one transceiver to be connected to the bus, that is, single station capability. The RS-485 interface allows up to 128 transceivers to be connected on the bus. That is, it has multi-station capability, so that users can easily establish a device network using a single RS-485 interface
Because the RS-485 interface has good anti-noise interference, long transmission distance and multi-station capability, it becomes the preferred serial interface. Because the half-duplex network composed of the RS485 interface generally only needs two connections, the RS485 interface adopts the shielded twisted pair transmission. The RS485 interface connector adopts DB-9 9-pin socket, and the RS485 interface of the intelligent terminal adopts DB-9 (hole), and the keyboard interface RS485 connected to the keyboard adopts DB-9 (pin).
STC RS232 and RS485 Serial cable advantage
1. Realize remote control of industrial field equipment;
2. Realize remote upgrade of device firmware, program upload and download, and flexible access to various device management platforms;
3. Realize the remote control of the industrial field touch screen and the remote mapping of the configuration screen;
STC RS232 and RS485 Serial cable catalogue
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Post time: Sep-02-2022