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Common sense of components: the plug in the market is called DRXX, the female is called DBXX, such as the serial port on our computer, called DR9 in the market, not DB9, many people are mistakenly called DB9, in fact DB9 is two An interface that connects two DR9s to each other.
In the article, I unified all serial device interfaces as RS232 interfaces.
RS-485 interface Because the RS232 interface standard appears earlier, it is inevitable that there are deficiencies, mainly the following four points:
(1) The signal level of the interface is high, which is easy to damage the chip of the interface circuit. Because it is not compatible with the TTL level, it needs to use the level conversion circuit to connect with the TTL circuit.
(2) The transmission rate is low. In asynchronous transmission, the baud rate is 20Kbps; therefore, in the "Southern 51CPLD development board", the integrated program baud rate can only be 19200, which is also the reason.
(3) The interface uses a signal line and a signal return line to form a common transmission form.
This common ground transmission is prone to common mode interference, so the noise immunity is weak.
(4) The transmission distance is limited. The standard transmission distance of Zui is 50 feet. In fact, it can only be used at 50 meters.
In view of the shortage of RS232 interface, there are some new interface standards, RS-485 is one of them, it has the following characteristics:
1. Electrical characteristics of RS-485: Logic "1" is represented by a voltage difference between two lines of +(2-6)V; logic "0" is represented by a voltage difference between two lines - (2-6)V . The interface signal level is lower than RS-232, and it is not easy to damage the chip of the interface circuit, and the level is compatible with the TTL level, which is convenient for connection with the TTL circuit.
2. RS-485 data zui high transmission rate is 10Mbps.
3. RS-485 interface is a combination of balanced driver and differential receiver, which has enhanced anti-common mode dry capability, that is, good anti-noise interference.
4. The RSi 485 interface has a standard transmission distance of 4000 feet, which is actually up to 3000 meters . In addition, the RS-232 interface allows only one transceiver to be connected to the bus, which is a 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 users can easily establish a device network with a single RS-485 interface.
Because of the half-duplex network composed of RS485 interface, generally only two connections (we are generally called AB line), so the RS485 interface is shielded twisted pair transmission.
RS232/RS485 conversion circuit
Since some devices are 232 interfaces, some are 485 interfaces. If a 232 interface device communicates with a 485 interface device, then a converter is needed to convert the 232 signal of the 232 interface device into a 485 signal. Then with
Device communication of 485 interface, this converter is RS232/RS485 conversion circuit. If two 232 interface devices are to be communicated over long distances, just add two RS232/RS485 conversion circuits.
The above RS232/RS485 conversion circuit adopts the stealing power technology from the computer serial port, which is called “passive RS232/RS485 conversion circuit†on the market, and “active RS232/RS485 conversion circuitâ€. The circuit schematic diagram is similar to the above picture. It’s just that the power supply has changed.
The difference between the communication interface R232 and RS485 of constant temperature and humidity test chamber
Many customers are purchasing our environmental testing equipment : constant temperature and humidity box , hot and cold impact box often considers the problem of connecting the computer to the computer. At present, all the equipments of our company can realize the computer connection through the external communication interface to print out the data and display curve. !
The RS232 interface is a standard for serial communication developed by the American Electronics Industry Association (EIA) in conjunction with Bell Systems, modem manufacturers, and computer terminal manufacturers in 1970. Its full name is "the serial binary data exchange interface technology standard between data terminal equipment (DTE) and data communication equipment (DCE)". The standard specifies a 25-pin DB25 connector for each connector of the connector. The signal content of the foot is specified, and the levels of various signals are also specified. DB25's serial port generally only uses 2 (RXD), 3 (TXD), and 7 (GND) pins. With the continuous improvement of the device, the DB25 pin is rarely seen now. Instead of it, it is DB9. Interface, the pin used by DB9 is different than DB25, which is 3 (RXD), 3 (TXD), and 5 (GND). So now the RS232 interface is called DB9.