Common types of interfaces for RFID readers

The communication interface is particularly important for the docking of information and products. The interface types of RFID Readers are mainly divided into two categories: limited and wireless. Wired interfaces generally have multiple communication interfaces, such as serial ports, network ports or other communication interfaces, and wireless interfaces are mainly connected with WIFI, Bluetooth, etc.

There are two types of reader interfaces:

1. Wired: USB, RS485, RS232, Ethernet, TCP/IP, RJ45, WG26/34, industrial bus, other customized data interfaces.

2. Wireless: Infrared, Bluetooth, WiFi, GPRS, 3G/4G, 433M, etc.

RFID reader interface - USB interface

Universal Serial Bus (English: Universal Serial Bus, abbreviation: USB) is a serial bus standard that connects computer systems and external devices. It is also a technical specification for input and output interfaces. It is widely used in personal computers and mobile devices. Information and communication products, and expanded to photographic equipment, digital TV (set-top box), game consoles and other related fields.

The new generation is USB 3.1, the transmission speed is 10Gbit/s, the three-stage voltage is 5V/12V/20V, the maximum power supply is 100W, and the new Type C plug type is no longer divided into positive and negative. USB interface shape USB power supply voltage USB communication speed USB to virtual serial port USB1.1 2.0 Transmission distance: within 10 meters

RFID reader interface - RS485

1. The electrical characteristic of RS485 is to use differential signal negative logic. The logic "1" is represented by the voltage difference between the two lines as +(2~6)V; the logic "0" is represented by the voltage difference between the two lines as -(2~6)V. 6) V represents. The interface signal level is lower than that of RS232-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 RS485 is 10Mbps.

3. The RS485 interface is a combination of a balanced driver and a differential receiver, which enhances the ability to resist common-mode interference, that is, it has good anti-noise interference.

4. The maximum communication distance of RS485 is about 1219m, and the maximum transmission rate is 10Mbps. The transmission rate is inversely proportional to the transmission distance. Only at the transmission rate of 100Kbps can the maximum communication distance be achieved. If you need to transmit a longer distance, you need to add 485 repeater. 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.

RFID reader interface - RS232

RS232 is one of the mainstream serial communication interfaces. Since the RS232 interface standard appeared earlier, it is inevitable that there are deficiencies, mainly in the following four points:

1. The signal level of the interface is high, and the chip of the interface circuit is easily damaged. The voltage of any signal line of the RS232 interface is a negative logic relationship. That is: logic "1" is -3~-15V; logic "0": +3~+15V, and the noise margin is 2V. That is to say, the receiver is required to recognize a signal higher than +3V as a logic "0", a signal lower than -3V as a logic "1", a TTL level of 5V as a logic positive, and 0 as a logic negative. It is incompatible with TTL level, so it needs to use level conversion circuit to connect with TTL circuit.

2. The transmission rate is low. During asynchronous transmission, the baud rate is 20Kbps; therefore, in the 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-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 in fact it can only be used at about 15 meters. The transmission distance is about 20 meters.

RFID reader interface - Ethernet

Ethernet works at the bottom layer, which is the data link layer. Ethernet is the most widely used LAN, including standard Ethernet (10Mbit/s), Fast Ethernet (100Mbit/s) and 10G (10Gbit/s) Ethernet. Ethernet is currently the most widely used LAN technology. It is not a specific network, but a technical specification. This standard defines the cable types and signal processing methods used in local area networks (LANs). Ethernet transmits information packets at a rate of 10 to 100 Mbps between interconnected devices. Twisted pair cable 10BaseT Ethernet has become the most widely used Ethernet technology because of its low cost, high reliability and 10 Mbps rate.

RFID reader interface - TCP/IP

1. TCP/IP (Transmission Control Protocol/Internet Protocol) is the transmission control protocol/Internet interconnection protocol, also known as the network communication protocol. It is the basic protocol of the Internet and the foundation of the Internet. The composition of the TCP protocol. TCP/IP defines the standard for how electronic devices connect to the Internet and how data is transferred between them. The protocol adopts a 4-layer hierarchical structure, and each layer calls the protocol provided by the next layer to fulfill its own needs. In layman's terms: TCP is responsible for discovering transmission problems, and sends out a signal whenever there is a problem, requiring retransmission until all data is safely and correctly transmitted to the destination. And IP is to specify an address for every networked device on the Internet.

2. The transmission distance can be very long (the transmission distance is related to the communication line).

RFID reader interface - RJ45

The RJ45 interface is usually used for data transmission, and the most common application is the network card interface. RJ45 is a type of various connectors. There are two ways to sort RJ45 connectors according to the line, one is orange-white, orange, green-white, blue, blue-white, green, brown-white, brown; the other is The types are green-white, green, orange-white, blue, blue-white, orange, brown-white, and brown; therefore, there are two types of lines using RJ45 connectors: straight-through lines and crossover lines.

RFID reader interface - WG protocol

1. The Wiegand protocol is an internationally unified standard and a communication protocol formulated by Motorola. It applies to many characteristics of readers and tags involved in Access Control systems. The standard 26-bit should be a commonly used format, and there are also 34-bit, 37-bit and other formats. The standard 26-bit format is an open format, which means that anyone can buy a HID Card in a specific format, and the types of these specific formats are open and optional. The 26-Bit format is a widely used industry standard and is open to all HID users. Almost all access control systems accept the standard 26-Bit format.

2. Transmission distance: within 10 meters.

3. Access control application

RFID reader interface - wireless transmission

1. Infrared

2. Bluetooth

3. WiFi

4. GPRS

5. 3G/4G

6. 433M and other wireless protocols

Of course, different RFID readers support different protocols depending on their usage. For example, if the transmission distance is short, the main wired interface generally used for communication within 20m is RS232. When the communication distance is tens of meters to thousands of meters, the RS485 standard is widely used.