This design uses ARM processor and embedded operating system μC/OS-II as the development platform in the system terminal. By using ARM processor, the CPU operating frequency can be up to 60MHz, which makes the data processing capability greatly enhanced. At the same time, based on embedding The software developed by the operating system μC/OS-II has strong scalability and stability.
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system structure
1 Function Introduction The car GPS navigation system obtains the latitude and longitude of the location at that time by the GPS system. The actual position at the time is obtained on the map through conversion and map matching. Then the user inputs the destination and calculates the shortest path through the A* shortest path algorithm. Display on the vector map, and extract the speed, time and other information provided by the GPS and display it on the screen.
2 system hardware structure The hardware core of the system is the 16/32-bit RISC processor STR710FZ2T6 chip in ARM7 series of STMicroelectronics. The chip has rich peripherals and enhanced I/O functions to meet low power consumption and high performance. Embedded system applications also have an external memory interface (EMI) that can address four memory segments, support multiple memory types such as SRAM, Flash, and ROM, while supporting multiple boot modes. It is very suitable for the development of embedded systems, the system is based on these characteristics of the chip. The system block diagram is shown in Figure 1.
Figure 1 hardware block diagram
The system is based on the STR710FZ2T6 microprocessor and uses two 512KB SDRAMs (IS61LV25616), one 8MB NAND Flash and one 2MB NOR Flash (SST39LF160). A GPS module for receiving GPS signals, a liquid crystal panel for display, and a keyboard input module are externally added.
1RS-232 serial communication interface circuit In the design of this paper, the system uses RS-232 serial interface for data transmission with the outside world. The circuit is shown in Figure 2. The STR710FZ2T6 has a full-duplex serial communication interface that enables data communication with the GPS module and uses the MAX3232 chip to convert between RS-232 levels and TTL levels.
Figure 2 serial communication circuit
SP3232E is an RS232 interface chip produced by Sipex. It is powered by a single power supply voltage. The power supply voltage can work normally from 3.0 to 5.5V, and its rated current is 300μA. Only need to externally connect four 0.1μF capacitors to ensure the data transmission rate maintains the RS232 output level at 120Kb/s, which can easily convert between TTL level and RS232 level.
2USB interface circuit In order to develop the USB function, the USB port is set first, and the interface circuit is shown in Figure 3.
Figure 3 USB interface circuit
3 ARM control module embedded development of the choice of hardware platform is mainly the choice of embedded processor, what embedded processor core used in a system depends mainly on the application domain, user needs, cost, development difficulties Factors such as ease of use. After determining which embedded processor core to use, the next step is to select a suitable processor based on the actual situation and consider the requirements of the system peripherals. In this design, the data processing and control module is the core control component of the vehicle-mounted terminal. It is an embedded system based on ARM microprocessor. Its main function is to process and control the components of the vehicle-mounted terminal, and follow the communication protocol. The requirements to perform the corresponding operations. The system includes CPU memory, I/O interfaces, and various control logic circuits. Combined with the actual situation of the current civilian vehicles, the STR710FZ2T6 microprocessor is selected, which adopts a high-performance 32-bit structure, featuring a high-density 16-bit instruction set and low power consumption, and combines the processor core with on-chip high-speed memory. The peripheral functions of the project are combined on a single microprocessor to provide a flexible, low-cost solution for a large number of computer embedded control applications.
4 GPS module The GPS module used in the system communicates with the microprocessor control module through asynchronous serial communication. Only two signal lines TXD, RXD and ground can be connected to the hardware connection for data transmission.
Serial communication uses a high communication voltage ±5 ~ ± 15V, often using ± 10V and ± 12V, and is a negative logic level, that is, the logic 0 level is specified as +5 ~ +15V, the logic 1 level is specified as - 15 to -5V, so the level conversion must be between the standard serial interface and the TTL/CMOS level.
In the design, the serial communication interface uses Maxim's MAX232 as the conversion chip. The MAX232 can convert two sets of serial signals. In this design, only one set is converted. TXD2 and RXD2 are connected to the peripheral GPS, and MCU_RXD is connected to the MCU_TXD and ARM processors. The four lμF charging capacitors connected to the MAX232 chip can work with an external 5V voltage.
Figure 4 shows the module
5 Display Module This design uses TG160128 liquid crystal display module with direct access. Connect the LCD module of the built-in 6963 controller directly to the P0 and P2 ports of the STR710FZ2T6. The read and write of the display module is controlled by the ARM read and write operation signals. The received and processed navigation information is then output to the Frame Buffer. At this time, the precise longitude, latitude and local time of the positioning point can be displayed on the display screen. The specific circuit is shown in Figure 4.
software design
1 Software data design The data in the navigation software is mainly the spatial data of the navigation map, which is mainly composed of some information related to navigation requirements, including road network geometry, road grade and service facilities.
2 software system design Navigation software is based on the navigation database. For the operation behavior of the navigation database, the navigation software is functionally divided into a part with navigation function and a part with browsing function.
3 Software interface design As mentioned above, the navigation software from the large function is divided into a part with browsing function and a part with navigation function. Therefore, two different interfaces have been designed: the browsing interface and the navigation interface.
Figure 6 thread diagram
4 embedded software design
The embedded system adopts the μC/OSII operating system. Since the processing function of the MCU is limited, multi-threading technology is adopted in the specific software implementation process, as shown in FIG. 6.
Industrial Ethernet switches are specifically designed to meet the needs of flexible industrial applications and provide a cost-effective industrial Ethernet communication solution. And its networking mode is more focused on loop design. The ring has the difference between single ring and multiple ring. At the same time, there are private ring protocols designed by various manufacturers based on STP and RSTP, such as RingOn, RingOpen open loop, FRP ring, turbo ring, etc.
The network management switch can be managed through the following ways: management through RS-232 serial port (or parallel port), management through web browser and management through network management software.
1. Management via serial port
The network management switch comes with a serial cable for switch management. First plug one end of the serial cable into the serial port on the back of the switch, and plug the other end into the serial port of an ordinary computer. Then power on the switch and the computer. The "Hyper Terminal" program is provided in both Windows 98 and Windows 2000. Open the "Hyper Terminal", after setting the connection parameters, you can interact with the switch through the serial cable. This method does not occupy the bandwidth of the switch, so it is called "Out of band" (Out of band).
In this management mode, the switch provides a menu-driven console interface or command line interface. You can use the "Tab" key or arrow keys to move through the menus and submenus, press the Enter key to execute the corresponding commands, or use the dedicated switch management command set to manage the switch. Switches of different brands have different command sets, and even switches of the same brand have different commands. It is more convenient to use menu commands.
2. Manage via web
The managed switch can be managed via Web (web browser), but an IP address must be assigned to the switch. This IP address has no other purpose except for the management switch. In the default state, the switch does not have an IP address. You must specify an IP address through the serial port or other methods to enable this management method.
When using a web browser to manage the switch, the switch is equivalent to a Web server, but the web page is not stored in the hard disk, but in the NVRAM of the switch. The Web program in the NVRAM can be upgraded through the program. When the administrator enters the IP address of the switch in the browser, the switch will transfer the web page to the computer like a server, and it will feel like you are visiting a website. This method occupies the bandwidth of the switch, so it is called "in band management" (In band).
If you want to manage the switch, just click the corresponding function item on the webpage and change the switch parameters in the text box or drop-down list. Web management can be carried out on the local area network in this way, so remote management can be realized.
3. Managed by network management software
Network management switches all follow the SNMP protocol (Simple Network Management Protocol), which is a set of network equipment management specifications that comply with international standards. All devices that follow the SNMP protocol can be managed through network management software. You only need to install a set of SNMP network management software on a network management workstation, and you can easily manage the switches, routers, servers, etc. on the network through the LAN.
The management of the network management switch can be managed in the above three ways. Which method is used? When the switch is initially set up, it is often through out-of-band management; after setting the IP address, you can use in-band management. In-band management Because the management data is transmitted through a publicly used LAN, remote management can be achieved, but the security is not strong. Out-of-band management is through serial communication, and data is only transmitted between the switch and the management machine, so the security is very strong; however, due to the limitation of the length of the serial cable, remote management cannot be realized. So which method you use depends on your requirements for security and manageability.
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