Development of handheld reader/writer based on EM4469 RFID card

RFID system mainly consists of radio frequency electronic tags, reading and writing equipment, computer network and software. Among them, the reading and writing equipment is mainly used as the radio frequency card data collection terminal. Its task is to start the radio frequency electronic tag as the data carrier and establish a two-way communication connection with the radio frequency electronic tag through space coupling, so as to realize the data transmission between the radio frequency electronic tag and the reading and writing equipment, and finally realize the reading and writing, storage and data transmission to the computer network of the radio frequency card. It is a very important hardware device in the RFID system.

Radio frequency electronic tag EM4469

EM4469 radio frequency card is a non-contact RFID radio frequency chip with a working frequency of 100kHz~150kHz and a read/write function launched by EM Microelectronics. It can provide a variety of data transmission rates and data encoding methods with low power consumption. Since the radio frequency chip is not only compatible with ISO 11784/11785 standards, but also complies with ISO FDX/B animal identification standards, the radio frequency chip can be widely used in various application management systems, especially animal identification and tracking management.

EM4469 has 32-bit password read/write protection, 32-bit unique ID code and 10-bit user code. The EEPROM storage space of EM4469 has 512 bits, which is divided into 16 sectors, each with 32 bits. The lock bit can turn the EEPROM data block into read-only mode. EM4469 can provide multiple data transmission rates and encoding methods with low power consumption, and its internal integrated resonant capacitor can be mask-selected, without the need for external capacitors. In addition, it has an on-chip rectifier and voltage limiter, and can operate at -40℃~85℃.

Handheld reader/writer design Handheld

reader/writer is also called portable reader/writer. It is a handheld computer that integrates RFID reading and writing functions, antenna and data processing functions. Its main part is the radio frequency card reading and writing circuit, which is used to realize radio frequency card reading and writing and data collection. In addition, it usually has an LCD screen and keyboard for inputting and displaying data, and is equipped with a memory and communication interface to save data and transmit it to the computer. In addition, it is also equipped with a stable power management circuit for powering the device.

Hardware design of handheld reading and writing equipment

The hardware circuit of the handheld reading and writing equipment mainly includes the main control microcontroller, radio frequency reading and writing, LCD display, storage, keyboard, communication, power supply and sound and light prompt circuit.

Main control microcontroller and radio frequency card

Reading and writing circuit design

Considering the large storage capacity of the handheld machine, the functional requirements of external interruption and timing interruption, and the cost of development tools, this system uses the STC89C58RD+ microcontroller produced by Shenzhen Hongjing Technology Co., Ltd. as the main control module. STC89C58RD+ has the following advantages: strong encryption; super strong anti-interference, there are three measures to reduce the external electromagnetic radiation of the microcontroller clock; ultra-low power consumption; online system programmable and remote upgradeable.

The radio frequency card reading and writing circuit is an important part of the handheld machine, which is used to realize the writing of radio frequency cards and read the data information carried by radio frequency cards. Here, the radio frequency card reading and writing module XM503A is used to realize the reading and writing control of the EM4469 radio frequency card (see Figure 1).

Figure 1 RFID card reader/writer circuit for handheld devices

LCD display circuit

The data display circuit in this handheld reader/writer device uses the CSD-12864I LCD display module. This is a graphic dot matrix LCD display module, which is mainly composed of row drivers and column drivers, as well as a 128×64 full-dot matrix LCD display. It can complete graphic display and can also display 32 16×16 dot matrix Chinese characters. The LCD display module and the CPU interface use an 8-bit data bus and 8 control lines.

During initialization, you must first enter the command to turn off the display screen, and then enter the command to turn on the display screen. Next, you can set the display start line and page address to enter the operation of reading and writing display data. [page]

Storage circuit hardware design

In this RFID handheld reader/writer device, the STC89C58RD+ microcontroller has only 1280B of RAM, and an additional memory circuit is required. This handheld device uses the HY628400 memory produced by Hynix.

HY628400 is a high-speed, low-power SRAM device with a capacity of 512k×8bit (4Mb in total). It uses advanced CMOS technology and is compatible with TTL input and output. The data retention mode ensures that the data is valid even when the minimum voltage is 2V.

In the 4Mb storage unit of HY628400, 2Mb of space is allocated to store Chinese character library for Chinese character display of LCD module; the remaining 2Mb of space is used to store data. The connection circuit between HY628400 and single-chip microcomputer is shown in Figure 2.

Figure 2 Connection circuit between STC89C58RD+ MCU and HY628400 memory

Design of other circuits

The RFID handheld reader and writer communicate with the computer through the RS-232C serial interface. This handheld reader and writer uses the MAX3243 chip that is compatible with the RS-232 standard. The MAX3243 has 3 drivers, 5 receivers and dual charge pump circuits, and all pins have ±15kV ESD protection.

The keyboard is the user's input port, and its function is to realize data input and control of handheld function selection and operation, thereby realizing human-computer interaction. This handheld keyboard has a total of 19 keys, including 10 numeric keys from 0 to 9, 5 function keys including F1, F2, F3, "." and Enter, backlight key, scan key (key for reading and writing EM4469), and power key.

The clock circuit is used to provide accurate time for the handheld device and can display the current time on the LCD screen. This handheld device uses the SD2003A clock chip produced by Shenzhen Weifan Electronic Technology Co., Ltd. It has the characteristics of small size, built-in crystal oscillator, support for I2C bus interface, etc. It can interrupt the output at a fixed time, high precision, no adjustment, and the annual error is less than 2 minutes (at 25±1℃).

The working voltage of this handheld reading and writing device is 5V, and the backup power supply voltage is 3.6V. Therefore, the boost DC/DC voltage converter MAX682 of Maxim Company is selected to power the handheld device. MAX682 can obtain a stable 5V output voltage and 250mA output current through an input voltage of 2.7V~5.5V, and the current consumption in the shutdown state is small (only 0.1mA), which fully meets the power supply needs of the handheld device. The circuit of the power module is shown in Figure 3, where C105 and C107 are filter capacitors, resistor R102 is a control resistor, and C106 is the boost capacitor of the circuit.

Figure 3 Power supply circuit

The sound and light prompt circuit includes two parts: buzzer and LED light-emitting diode circuit, which are used to indicate successful operation of the handheld device or various warning status prompts. [page]

Software Design

This handheld reader and writer mainly completes the reading and writing of radio frequency electronic tags, data storage and information communication with the computer. The flow of the handheld main program is shown in Figure 4.

Figure 4 Main program flow chart

The handheld reader/writer developed in this paper uses Manchester encoding to read the data of EM4469, and the data transmission rate is RF/64.
The XM503 induction module completes the reading and writing operations of the EM4469 radio frequency card by sending standard commands. The program flow of the card reader is: first initialize the serial port of the microcontroller, send the command to open the radio frequency field, and enter the area code of the data sector to be read. Then send the command to read the data to determine whether the command has been sent. If it has not been sent, continue to send; if the sending is completed, then determine whether there is data. If there is no data, prompt an error and return to the initialization location. If there is data, start receiving. Finally, determine whether the received data is correct or not. If it is correct, the read data can be displayed on the LCD screen. If it is determined that the received data is wrong, prompt an error and return to initialization.

When writing data to the EM4469 radio frequency card, first initialize the serial port of the microcontroller, set the baud rate, and send the command to open the radio frequency field. Then enter the area code of the sector to which the data is to be written and send the command to write data, and then determine whether the command to write data has been sent. If the transmission is not completed, continue to send; if the transmission is completed, further determine whether there is data. If there is no data, an error message will be prompted and return to initialization; if there is data, start receiving the data to be written. Then determine whether the received data is correct or not. If the received data is judged to be wrong, an error message will be prompted and return to the initialization place; if it is correct, it must be read out to determine whether it is the data to be written. If it is, it ends; if not, it returns to initialization.

Conclusion

This article discusses in detail the hardware circuit design and the design method of the main software part of the handheld reader and writer based on the EM4469 radio frequency card. The product adopts a modular structural design method to design the radio frequency card reading and writing circuit into a relatively independent module. If there is a need to use different types of radio frequency cards, this part of the circuit can be replaced with other types of radio frequency card reading and writing circuit modules to meet the needs. ■

References
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2. Lang Weimin. Principle and Application of Radio Frequency Identification (RFID). Beijing: Machinery Industry Press, 2006.10-60
3. www.szforen.com, EM4469DATASHEET, 2006,3
4. You Zhanqing, Liu Kesheng, Zhang Yiqiang, et al. Planning and Implementation of Radio Frequency Identification Technology (RFID). Beijing: Publishing House of Electronics Industry, 2005.20-47, 50-78