ã€Abstract】 Combined with the existing vehicle monitoring terminal solutions, the overall design of the vehicle monitoring terminal based on CDMA module is determined, the system composition and function modules are introduced, the system hardware design and the corresponding functional unit software are given design.
With the development of wireless communication technologies, Intelligent Transport System (ITS) has been widely used. ITS generally includes four parts: traffic information collection part, vehicle scheduling control part, electronic toll collection system and traffic information service. Four of these parts require the participation of vehicle-mounted terminals, which are very important parts in the ITS system. The traditional vehicle monitoring terminal system usually adopts the GSM / GPS scheme. This kind of scheme has low cost and has been successfully applied in some fields. The most important function of the vehicle-mounted terminal is the collection of traffic information, providing accurate positioning of the vehicle and vehicle operation (including speed information, direction of travel, etc.). The positioning information and speed information are usually obtained by an external GPS module, but when the vehicle enters a tunnel or is parked next to a tall building, the vehicle is in the blind area covered by GPS satellites. During this time, the dispatch center cannot accurately obtain the traffic of the vehicle Information affects the reliability of the monitoring and scheduling system. This paper proposes a vehicle monitoring terminal system using ATMEL 89S51 as the controller and CDMA module DTGS800 as the communication and positioning system platform.
1. Introduction to DTGS-800
DTGS800 is a CDMA wireless communication module produced by AnyDATA.
DTGS800 works in the 832MHz frequency band, with a power consumption of 0.32W, has a data transmission rate of up to 153kbps, can be controlled remotely by AT commands, and has a built-in TCP / IP protocol stack to provide short message services. A chip with gpsOne function is integrated inside the module, and the gpsOne solution can be used to realize the positioning function.
The main interfaces of the DTGS800 module include: universal asynchronous serial port UART, universal I / O port GPIO, codec interface CODEC, user interface User Interface, PM interface.
2. System hardware design
The vehicle monitoring terminal is mainly used for real-time information interaction with the monitoring center, including:
Obtain vehicle position information and speed information; issue scheduling information; perform remote control in the event of vehicle abnormalities. In addition, it provides mobile communication services to vehicle drivers. This module can be used to make and receive calls, and even make three-way calls. Its hardware system is an embedded single-chip system that comprehensively utilizes electronic technology and communication technology, and is mainly composed of a controller and a communication module.
The controller is the core of the vehicle monitoring terminal, and it has a great influence on the safe operation and reliability of the entire system. In this design, the CPU selects the 8-bit microcontroller 89C51RD2 of ATMEL, which is a high-performance CMOS FLASH version of the CMOS single-chip 8-bit microcontroller 80C51. Its features include: 1 64-Kbyte FLASH storage area for storing code and data; 256 bytes of internal RAM, 1 9-source 4-level interrupt controller and 3 timers / counters; 1 1792 bytes of XRAM , 1 hardware watchdog timer, SPI interface, keyboard, 1 more general-purpose serial channel, easy for multi-processor communication (EUART) and acceleration mechanism (X2 Mode).
This CPU uses a fully static design, reducing system power consumption, allowing the clock frequency to be reduced to any value without causing data loss. There are also two software-selectable operating modes that reduce the active state of the 8-bit clock divider, further reducing power consumption. In idle mode, the CPU is frozen, while peripherals and interrupt systems continue to work. In power-down mode, the RAM contents are saved, and all other functions are invalid.
The frame diagram of the system is as follows:
Figure 1 System structure framework
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