Introduction Radio Frequency Identification (RFID) technology, an automatic identification technology that emerged in the 1990s, is a technology that uses radio frequency signals to achieve contactless information transmission through spatial coupling (alternating magnetic or electromagnetic fields) and uses the transmitted information to achieve identification purposes. Compared with earlier identification technologies (barcodes, magnetic cards, etc.), it has outstanding features such as non-contact identification (reading distance can range from 10cm to tens of meters), large storage capacity, ability to identify high-speed moving objects, resistance to harsh environments, strong confidentiality, and the ability to identify multiple objects simultaneously. Therefore, it can be applied in a wider range of situations. Currently, there are three main design methods for UHF RFID readers: design using discrete high-frequency components, integrated RFID chip design, and OEM methods to complete the RFID module. Designing readers using discrete high-frequency components is very difficult in terms of circuit design and debugging, and requires high-end development equipment. In response to this situation, many chip manufacturers have successively developed UHF integrated chips, such as Melexis's low-power FSK/FM/ASK transceiver chip TH71221, but no corresponding development evaluation board has been provided, and development still faces certain difficulties. Meanwhile, many manufacturers have launched UHF RFID modules, allowing users to produce their own UHF readers through OEM methods, reducing development difficulty and shortening the development cycle. RFID System A typical RFID system mainly consists of three parts: the application system, the RFID reader, and the RFID tag (Figure 1). The RFID tag and the RFID reader are respectively the information carrier and the information acquisition device, and the RFID system they constitute ultimately serves the application system. The application programming interface (API) between the RFID reader and the application system is usually represented by a set of standard interface functions that can be called by application system development tools (such as VC++, VB, PB, etc.). UHF RFID Reader Design The RFID reader is mainly divided into two parts: the control module and the RFID module. In an RFID system, the RFID reader's task is to transmit a read signal to the tag through the RFID module, receive the tag's response, decode the tag's object identification information, and then transmit the object identification information along with other relevant information on the tag to the application system computer for processing through the control module. In this design, after comparing many RFID transceiver modules, the Skymodule M8 module developed by Skyteck was finally selected. The M8 module provides a low-power, high-performance, and high-efficiency UHF reader design platform. It is a multi-protocol OEM module capable of reading and writing UHF tags in the frequency range of 860–960MHz that meet ISO18000-6 A/B, EPC Class 0/0+ or ​​1, EPC Class 1 Gen2, and other protocols. New tag protocols and compatibility can be added in the field through firmware upgrades. The M8 module's RF output power can be set programmatically between 15mW and 500mW. At 5V, the M8 module's intelligent power management keeps the current below 100μA (sleep mode), allowing the device to be powered by battery. To simplify operation, the module features a 20-pin interface. Only the relevant control module needs to be designed according to the specific application and connected to the interface via wires to exchange data with the M8 module using the specified communication method. Interfaces with the control module include UART (TTL), I2C, and SPI, and it can also communicate directly with a computer via RS-232 and USB interfaces. The M8 module has a built-in portable antenna and a 50Ω output impedance for connecting to an external antenna. The module's reading distance is directly related to the external antenna. Its appearance is shown in Figure 2. Control Module Design As shown in Figure 1, the control module mainly consists of two parts: a control unit based on a microcontroller (such as a single-chip microcomputer) and a communication interface unit. The main function of the control unit is to configure the RF module and communicate with it to obtain the RF tag information acquired by the RF module. It then uploads the acquired tag information to the host computer through the communication interface and can also receive configuration commands from the host computer for the RF reader. Furthermore, the RF reader needs to have an interface for direct communication with the computer, which is beneficial for the design and development of the host computer software. Therefore, the microcontroller for the control unit needs to be selected according to the functional requirements of the control unit, and various communication interfaces need to be implemented. Here, the control unit is a microcontroller system based on the AT89S53 microcontroller. This microcontroller contains 12KB of Flash Memory and 256Bytes×8 of RAM, three 16-bit timers/counters, nine interrupt sources, a programmable serial UART channel, and an SPI interface. The communication interface unit can be divided into two parts: a chip-level bus interface unit (the M8 module supports I2C, SPI, UART, etc.) and a fieldbus-level interface unit (RS232, RS485, CAN bus, etc.). The control unit uses the chip-level bus interface unit to configure the RF module and read the RF tag information captured by the RF module. In this design, the control module needs an interface, which connects to the microcontroller's SPI pin on one hand and to the M8 module via a wire on the other, thus realizing communication between the control module and the M8 module. To transmit the collected tag information to the host computer, the control module can communicate with the computer via a serial port. The circuit schematic of the control module is shown in Figure 3. Software Design The microcontroller software in this design is mainly divided into two parts: SPI communication between the microcontroller and the M8 module, and serial communication between the microcontroller and the host computer. Skyteck has developed a dedicated communication protocol for the M8 module. The microcontroller only needs to follow the communication protocol format to communicate with the M8 module via the SPI interface, read tag information, or configure the M8 module. To achieve communication between the microcontroller and the computer, a communication protocol also needs to be developed. This allows the microcontroller to transmit the acquired tag information to the computer according to the communication protocol format. Users can then develop corresponding computer software to manage the tag information based on specific applications. Conclusion Currently, the author has designed an RFID card reader using the M8 module and applied it to a long-distance personnel attendance system by selecting a suitable antenna. The card reader collects personnel information non-contactly and then transmits the information to the host computer, enabling effective personnel management, including browsing, querying, statistical analysis, and modification of employee information in the database. The card reader is convenient to operate and reliable in practical applications.