Radio frequency IC card system based on USB interface

The RF IC card, a contactless IC card, is a new technology developed in recent years. It combines RFID technology and IC card technology to solve the problem of passive (no power in the card) and contactless technology. It has the advantages of convenient use and long life, and is widely used in daily life.

In the past, the IC card system's card reader and the host management machine communicated with each other, usually using the serial port RS2232, but the RS2232 serial port has a slower data transfer rate, while the RF card machine has a large amount of recording per day, and a data collection point is often To correspond to multiple card readers, it is desirable to speed up the data transfer rate between the PC and the card reader.

USB is a new type of interface that supports plug and play. The data between the main system and the USB peripheral device is transmitted through a 4-pin probe. It has the advantages of fast transmission speed, hot swappable, easy to expand and easy to use. The USB interface transmits much faster than the serial port. The data transfer rate of the USB v1.1 specification can reach 1.5 MbPs to 2 MbPs, and the transfer rate specified by USBv2.0 is 360 MbPs to 480 MbPs. Because of the advantages of the USB interface, it has gradually become a trend in the connection between PCs and peripherals. When we improved the JS201 RF card validator developed by ourselves, we decided to use the USB interface to communicate with the host management machine.

1 hardware design

1.1 System structure and working principle

The structure of the RF IC system is shown in Figure 1.

RF IC system structure

Figure 1 RF card system block diagram

The whole system takes the 8051 MCU as the core, and it completes the functions of communication, storage management, input and display with the read/write module. When using, when the user swipes his own RF card through the magnetic field sensing area of ​​the vehicle card reader, the RF card system reads the card number, amount, password and other information of the RF card, first correct the password and the card is legal. Sexual discrimination. If it is a legal card, the card reader calculates the remaining amount of the RF card according to the existing settings, and then writes the corresponding data back to the card to ensure the correctness and security of the card operation.

The RF card reading module of the RF IC card system developed in this paper uses the RF read/write chip P4095. The P4095 integrates a PLL system to perform adaptive adjustment of the antenna's resonant frequency, and does not require external crystal support. It has a carrier frequency range of 100 kHz to 150 kHz, which is used to complete the on-board card reader and RF card information. Exchange. In actual operation, the RF card itself does not have a power supply and needs to extract energy from the RF signal sent by the reader P4095. Therefore, during the reception of the data by the RF card, on the one hand, it demodulates the data information from the received signal according to the originally agreed coding mode (according to the Manchester coding law), and on the other hand extracts the energy from the received signal. Because the RF card is coupled to the antenna of the application terminal by load modulation, when the RF card returns data, the P4095 continuously transmits the 125 kHz RF carrier signal, so that the reader can obtain the information in the RF card. Then, the received information is sent to the single chip microcomputer, and the data is processed and saved by the single chip computer according to the wireless specification protocol of the radio frequency card.

1.2 USB interface circuit design

At present, there are two main schemes for designing instruments with USB interface: one is to directly use a microcontroller with its own USB port, such as Cypress's EZ2USB MCU, Intel's 8X930, etc.; the other is still using ordinary MCU, but increase A USB interface chip to handle USB communication. The former is integrated with the USB interface chip, so the development is simpler, but the price is higher, and a special development system is purchased. The latter must have another microprocessor to control, but its price is cheap and the design is simple. It is especially suitable for product modification design. When modifying the hardware, only the port connection needs to be changed, and a small number of components can be added. As long as the microprocessor's USB protocol processing and data exchange procedures are added, there is no need to make major changes to the original product. Therefore, we use the latter scheme to improve the original RF IC card system.

National Semiconductor's USBN9603 is used as the USB interface control chip. It integrates a USB transceiver to meet the electrical performance requirements of the transmission. It also integrates the Serial Interface Engine (SIE), which is mainly responsible for clock recovery and packet end detection. CRC codec and node status recognition. It is physically connected to the host through four lines: VBUS, GND, D+, D-. Among them: VBUS is the bus power supply, which can provide +5 V power supply to USB peripherals; GND is ground; D+ and D- are data lines, USB uses D+ and D- two data lines, and transmits signals by differential signal transmission Data, support for high speed or low speed transmission mode. In addition, there are a total of seven transmit/receive FIFO buffers inside the chip: one bidirectional transmit and receive FIFO buffer, three unidirectional transmit FIFO buffers, and three one-way receive FIFO buffers. Its connection to the microcontroller is shown in Figure 2.

MCU and USBN9603 interface circuit

Figure 2 MCU and USBN9603 interface circuit

When the 8051 MCU operates the USBN9603, the IOMS is controlled by P1.0, which is set to the IPO port access mode, and the port data is read and written by A8~A15 according to the RD and WR signals in conjunction with the A0 level state. The port access adopts the interrupt mode, that is, the USBN9603 generates an interrupt request signal to the INTO of the 8051 MCU, and the 8051 determines the type of the interrupt generated by reading the US2BN9603 related register, thereby executing the corresponding interrupt processing program.

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