Abstract: This paper describes RF-based wireless transceiver SoC nRF9E5 system framework, the various components, working methods and configuration methods. On this basis, designed by nRF9E5 and 4 dot matrix LCD module consisting of a simple two-way remote control door lock display system.
  Key words: two-way remote keyless entry; wireless transceiver system; LCD
  Introduction
  Automotive remote keyless entry (remote keyless entry, RKE) has become an integral part of the car. RKE for improving security and controlling the car is important. In the past one-way RKE system consists of the design of a control terminal end and an execution component, the biggest inconvenience of this system is that only the user to send messages to the door, and the door can not be your own feedback to the user, which allows users to not know the car conditions, to the car's safety and security. In addition, the system powered by battery power consumption is a bigger issue. In order to solve these two problems, we design a wireless transceiver chip based on chip 12864-12 nRF9E5 and LCD two-way RKE system implementation.
Figure 2 nRF9E5 with dot matrix LCD Interface Schematic
  Figure 4 receive lower computer program flow
  nRF9E5 Features
  nRF9E5 is a Nordic company launched the system-level RF chip, the built-in nRF905 43 3/868/915 MHz transceiver, 8051 compatible microcontroller and a 4 input 10-bit 80ksps ADC, with its built-in nRF905 transceiver chip transceiver nRF905 Like, you can work in ShockBurst (automatic processing of the prefix, address and CRC) method. Built-in voltage regulator module, the maximum noise suppression, for the system to provide 1. 9 ~ 3.6V operating voltage.
  nRF9E5 of the chip micro-controller has one and the same serial port 8051, you can use Timer 1 and Timer 2 as a baud rate generator asynchronous communication. The data contained in the microprocessor RAM 256B and 512B of the ROM, also extends the two data pointers to facilitate the read data from the XRAM area. Power-on reset or software reset, the processor automatically in the boot ROM code. User programs are usually under the guidance of the boot sector, from the EEPROM is loaded into a 4KB RAM, 4KB of RAM that can be used to store data.
  nRF9E5 integrated transceiver chip, which can be internal or internal SPI parallel port to communicate with other modules, with a single-chip radio transceiver nRF905 with the same functionality. Transceiver chip parallel through the port or SPI communication with a microcontroller. nRF9E5 a complete transceiver from the frequency synthesizer, a power amplifier, a regulator and two receiver components. Output power, channel, and other RF parameters can be of special function register RADIO (0xA0) program to control it. In transmit mode, RF current is 11mA, receive mode is 12.5mA. For energy, the transceiver can be programmed on / off.
  Two-way RKE system hardware components
  Two-way RKE system consists of data terminal and the main transceiver is composed of two parts. Where the data is the user portable terminal, can be understood as a remote control key, and the main transceiver is installed inside the door, used to open the door. Data terminal and the main data communication between the transceiver is carried by nRF9E5 to. As nRF9E5 built-in microcontroller and the amount of data transmitted is not very big, so RKE system does not require other additional micro-controller, the memory does not need to extend the other, making the system hardware structure is very simple. The two-way RKE system shown in Figure 1.
  The master transceiver and data terminals are available through RS-232 or USB interface with PC connected, you can achieve the communication between the PC and nRF9E5, so that the data terminal through the PC character to be displayed (alarm messages) to the form of ASCII written to the data terminal of the memory, when the car alarm when necessary, the information data terminal will raise the alarm, and then through the LCD display. You can also pre-cured PC all the commands to the hardware, when the user only needs to key operation by the hands of two-way data transmission can be achieved.
  The client's data terminals, the use of the LCD is dot matrix liquid crystal display 4, the internal control and display module are the CMOS drive circuit, CMOS circuit is a low-power devices, and nRF9E5 also use CMOS structure, it eliminates the need microcontroller and display driver circuit between the module directly connected the two. The hardware interface shown in Figure 2. Interfaces according to the figure, the power, LCD automatically reset to 8 bit data bus, single display, the display lights up the left 8 and right 8-bit off. In the initial program command must be used in LCD set into 4-bit data bus, dual-line display, the display of the left and right 8-bit 8-bit are in working condition.
  In addition, nRF9E5, its biggest advantage is a carrier detection. When the transceiver is ready to send data, it first goes into receive mode and to detect the work of the channel is free. Carrier testing standards are generally lower than the sensitivity of 5 dBm, for example, a sensitivity of -100 dBm, carrier detection carrier detection as low as -105 dBm. In other words, the carrier is lower than -105 dBm, the carrier detection signal is low (usually 0), higher than -95 dBm, the carrier detect signal is high (typically VDD), ranging between -105 ~ -95 dBm , carrier detect signal may also be high for low. This feature is well to avoid the same operating frequency of the different transmitter collisions between data packets, to effectively prevent the signal interference. Improve the stability of the wireless transceiver keys.
  In addition, the system still need to add a simple buzzer. When the system requires the alarm, the buzzer to beep at a time when the alarm information is displayed on the LCD.
  System Software Design
  Communication Protocol
  To achieve lock / unlock and security alarm, you must complete the data terminal and the main transceiver wireless data communication between. Various parts of the system is serving the wireless data transmission for this purpose. Therefore, in the whole system software design, wireless data transmission is the most important part. Wireless transmission way of data frames, data frame format shown in Table 1.
  Preamble useful data is mainly used to prevent interference; ID is mainly used to mark a specific vehicle information in order to correctly identify, and if ID does not match the data frame will be ignored; information code used to indicate the user's operations that include the lock, unlock, display alerts. When the user sends the appropriate commands to perform separate lock, unlock, and when users send and receive out of the range, the main transceiver can automatically send a warning message; check code is used to test the data received is correct, incorrect, the need to retransmit data frames.
  Software process
  Because the data terminal and communications between the main transceiver is duplex, so in actual system operation, data transmission is constantly changing direction. Therefore, to achieve the coordination of communications both sides, we must design a more appropriate send and receive order. To better illustrate the program flow, where the user side as the host computer data terminal, and the car's main transceiver as the next crew. Host computer and slave receive process in Figure 3, Figure 4.
  Conclusion
  Formed using two-way RKE nRF9E5 wireless data transmission system does not require an external microcontroller part, does not need external memory expansion; when and dot matrix LCD is connected, do not need an external drive, which greatly reduces the complexity of the system. In addition the system is used in lower energy consumption module, which to some extent to achieve the low power requirements of the system. This two-way RKE system designed to improve the security of data transfer, and coupled with the display can be more directly reflects the state of the car. However, there are imperfections in the system, if the system coupled with a DAC, coupled with the speaker to be more intuitive information about the car back to the user. In addition, if coupled with a pressure sensor inside the door, can significantly prevent the car being damaged artificially, to further improve vehicle safety.