As an advanced automatic identification and data acquisition technology, Radio Frequency Identification (RFID) has been widely used in manufacturing, logistics management, public safety and other fields, and has promoted the development of literacy tools and various application products and systems. , production and promotion of applications. At present, there are two ISO standards in the field of radio frequency identification technology applied to 13.56 MHz in China, one is IS014443 and the other is ISO15693. ISO14443 defines two types of protocols, TYPE A and TYPE B. The communication rate is 106 kb/s. The difference between them is mainly the modulation depth of the carrier and the encoding mode of the bit. ISO15693 read and write distance is far, while ISO14443 read and write distance is slightly closer, but the latter is more widely used. The cards of these three protocols have a wide range of applications in various fields, and the existing 13.56 MHz RF card readers in the country generally support only one protocol and have a single function. Based on this situation, this paper proposes a design scheme based on TI's TRF7960 RF chip and Hongjing's STCllF32XE high-speed single-chip microcomputer to design multi-protocol RF card reader. A peripheral device such as a dot matrix liquid crystal LCD, a serial memory W25X80, and a USB chip PL2303 is expanded on the card reader. The LCD can display various graphics and Chinese characters. The serial memory is used to store dot matrix fonts, graphics libraries, etc. The USB chip allows the card reader to eliminate the serial port and the power supply port, and can communicate with the PC management software through the USB interface. The card reader is convenient to use, simple, low in cost, stable in circuit operation, and can be applied to various occasions.
1 card reader hardware designSTCllF32XE MCU is a single clock/machine cycle (IT) MCU designed and manufactured by Hongjing Technology Co., Ltd. It is a new generation 8051 MCU with high speed, low power consumption and super anti-interference. The instruction code is fully compatible with the traditional 8051, but the speed is 8~. 12 times. The internal integrated high-reliability reset circuit can be used in high-speed communication, intelligent control, strong interference and other occasions. The STCllF32XE has 32 KB of Flash, 29 KB of EEPROM and 1 280 bytes of SRAM. The STCllF32XE used in this article is the LQFP-44 pin. In addition to the EA, ALE, PSEN, and RST pins, which can be defined as general-purpose I/O, there is one more P4 port. Programming supports ISP download function, which is convenient to use.
The TRF7960 is one of a series of high frequency (13.56MHz) multi-standard radio frequency identification (RFID) reader ICs from TI (Texas Instruments). The TRF7960 features an ultra-small 32-pin QFN advanced package design that supports ISO/IEC 14443A/B, ISO/IEC 15693, ISO/IEC 18000-3, and TI's contactless payment business and Tag-It transponder product line. The TRF7960 reader provides an internal clock for the microcontroller, which requires only one 13.56 MHz crystal to operate without the need for two standard crystals, helping to reduce the total material of the terminal reader product. Single cost. Due to the small number of components, the reader IC consumes less power and takes up less space, so sensitivity and noise attenuation can be solved. Other integrated features include fault checking, data formatting, framing, and anti-collision support for multi-reader environments. The TRF7960 communicates with the microcontroller using 8-bit parallel or serial (SPI) flexible communication. The chip also has a wide operating voltage (2.7 to 5.5 V). The TRF7960 is ideal for applications such as secure access control, product certification, and contactless payment systems.
In order to use the internal 1 KB extended SRAM of STCllF32XE microcontroller, the 8-bit parallel analog bus interface mode is adopted here. The P1 port of the single chip microcomputer is connected with the DO~D7 of TRF7960, and P2.6, P2.7 and P3.2 are used. The control lines are connected to the DATA CLK, EN, and IRQ pins of the TRF7960. Note that in order for the TRF7960 communication interface to support a logic level of 5 V, the VDD_I/O pin of the TRF7960 should be connected to 5 V. The use of the analog bus method is a general method, especially for microcontrollers that do not support bus expansion. The analog bus is used in this design to prevent bus collisions between the TRF7960 and the SRAM inside the microcontroller. Figure 1 is a schematic diagram of the system hardware of the card reader.
PL2303 is a USB bus adapter chip produced by Prolific: The company can realize USB to serial port, which is used to expand asynchronous serial port for computer, or upgrade ordinary serial device directly to USB bus. The PL2303 is fully compatible with USBl. 1, USB2.0; 3 ~ 5 V adjustment output, can meet different voltage output interface; full duplex transmission and reception (RXD, TXD); MODEM control line (RTS, CTS, DTR, DSR, DCD and RI); 5, 6, 7 or 8 bit data format; parity or no parity; 1 bit, 1 bit half or 2 stop bits; programmable baud rate 75 b / s ~ 6 Mb / s and so on. As a result, the PL2303 is ideal for mobile and embedded systems, and its small package can be embedded in any connector and handheld device. The PL2303 has low power consumption in both active mode and sleep mode, making it ideal for bus-powered applications. The USB chip allows the card reader to eliminate the serial port and power supply port, and can communicate with the PC management software through the USB interface.
The display uses a graphic dot matrix LCD module based on the ST7565S controller with a resolution of 128 & TImes; 64, supports serial interface, without Chinese character library. In order to enable the card reader to be used in applications such as library library management and other occasions requiring Chinese character display, the serial memory W25X80 produced by Winbond was used to design the GB2312 Chinese character library and other image libraries. Serial Flash memory is favored for its small size, high density, low power consumption, low price and simple operation. Winbond's Flash memory W25X80 is 8 Mb serial Fla-sh, which is 1 MB in size and is divided into 4096. Page, each page is a 256-byte memory unit with a 256-byte buffer and SPI interface. Designing a Chinese character library using Flash is not only easy to operate, but also flexible enough to apply to multiple design scenarios.
The system hardware circuit design should pay attention to the following:
1 Try to make the filter capacitor close to the chip, especially the 10 nF capacitor, so as to effectively filter the high frequency signal;
2 Try to reduce the loop of the wiring ground, so the grounding via is required to be as close as possible to the grounding end of the component or IC;
The placement of 32 inductors should be in the 90° direction, which mainly reduces the coupling between the two inductors;
4 digital ground and analog ground are preferably in different places, preferably connected by magnetic beads or inductors;
5 Ensure that the middle part of the chip is sufficiently grounded. You can make 9 holes on the board to allow the chip to be fully grounded and cooled.
6 When wiring, try to reduce the length of the auxiliary line, especially the RF front end, so that the components remain compact, and the RF output front end should preferably maintain a smooth output;
7 It is best to add some test points in the circuit to facilitate adjustment of the hardware circuit;
8 Try to avoid passing digital signals in the RF line.
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