Common Communication Interfaces in RFID Devices

　　Common Communication Interfaces in RFID Devices

　　In data communication, computer network and distributed industrial control system, serial communication is often used to exchange data and information. The communication interface is particularly important for the connection of information and products. Therefore, the editor will now analyze several common interface protocols for you!

　　1. RS232

　　RS-232 is a serial physical interface standard developed by EIA (Electronic Industry Association). RS is the abbreviation of "Recommended Standard" in English, and 232 is the identification number. RS-232 is a regulation on electrical characteristics and physical characteristics. It only acts on the transmission path of data, and it does not contain the processing method of data.

　　The standard stipulates that a 25-pin DB-25 connector is used, and the signal content of each pin of the connector is specified, and the level of various signals is also specified. Later IBM PCs simplified RS-232 to a DB-9 connector, which became the de facto standard today. The RS-232 port of industrial control generally only uses three lines of RXD (2), TXD (3), and GND (5).

　　The data transmission rate specified by the RS-232-C standard is 50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600, 19200 baud per second. The RS-232-C standard stipulates that the driver is allowed to have a capacitive load of 2500pF, and the communication distance will be limited by this capacitance. For example, when a communication cable of 150pF/m is used, the maximum communication distance is 15m; if the capacitance per meter of the cable is reduced , the communication distance can be increased. Another reason for the short transmission distance is that RS-232 is a single-ended signal transmission, and there are problems such as common ground noise and inability to suppress common mode interference, so it is generally used for communication within 20m.

　　2. RS485

　　When the communication distance is required to be tens of meters to thousands of meters, the RS-485 serial bus standard is widely used. RS-485 adopts balanced transmission and differential reception, so it has the ability to suppress common mode interference. In addition, the bus transceiver has high sensitivity and can detect voltages as low as 200mV, so the transmission signal can be recovered from kilometers away. RS-485 adopts half-duplex working mode, only one point is in the sending state at any time, therefore, the sending circuit must be controlled by the enable signal. RS-485 is very convenient for multi-point interconnection, which can save many signal lines. The application of RS-485 can be networked to form a distributed system, which allows up to 32 drives and 32 receivers in parallel.

　　Has the following characteristics:

　　1) Electrical characteristics of RS485: 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 RS232C, 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.

　　2) The maximum data transmission rate of RS485 is 10Mbps

　　3) The RS485 interface is 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 maximum communication distance of RS485 is about 1219M, and the maximum transmission rate is 10Mb/S. The transmission rate is inversely proportional to the transmission distance. The maximum communication distance can only be achieved at a transmission rate of 100Kb/S. Distance, need to add 485 repeaters. The RS485 bus generally supports a maximum of 32 nodes. If a special 485 chip is used, it can reach 128 or 256 nodes, and the maximum can support 400 nodes.

　　Because the RS485 interface has good anti-noise interference, long transmission distance and multi-station capability, the above-mentioned advantages make it 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, the RS485 interface connected with the intelligent terminal adopts DB-9 (hole), and the keyboard interface RS485 connected with the keyboard adopts DB-9 (pin).

　　Based on the advantages of multiple serial ports, Gaote Electronics has launched a multi-serial port star product: UHF four-port RFID reader, (product model: C216022). This is a high-performance multi-serial UHF Gen2 reader. The UHF reader has four communication interfaces: RS232, RS485, TCP/IP, digital input/output, which can meet the development needs of different system projects to the greatest extent.

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