At present, with the rapid development of the information industry, all kinds of ships need to be equipped with more quality and low-quality small and medium-sized information monitoring terminals, which are used to monitor weather conditions to obtain navigation information to ensure sailing safety. 32-bit processors led by ARM, MIPS, show great advantages in information monitoring terminal applications, but generally constructing an embedded system constructed in 32-bit processors often needs to configure external flash and sdram so that development and maintenance The overall system is high, this design uses high-performance low-power AVR microcontrollers and LCD liquid crystal modules to design information monitoring terminals, which have the advantages of low price, stable performance, clear display, good human-machine interface, and meet the shipping Small information monitoring terminal needs.
1 overall design
The information monitoring terminal is mainly composed of display control board, keyboard, communication interface, and liquid crystal display module. It has functions such as data transmission, data display, human-computer interaction, and screen brightness adjustment, as shown in Figure 1.
After the system is initialized, the information monitoring terminal receives data from the communication interface according to the set mode of operation, and then transmits the data to the LCD liquid crystal display through the LCD controller, responds to the user's operating instructions through the keyboard and the display.
2 hardware design
2.1 LCD module and microcontroller
The liquid crystal display module selects EW32F00BCW, which is a liquid crystal display of 5 inch 320 × 240 dot matrix. Performance is comparable to the original DMF50081 of Japan, but the price is much cheaper. The device is displayed in a CCFL backlight, and the display mode is full transmissive, and the display color is blue, the outer size is 139.0 W × 102.5H × 13.2dmm.
The microcontroller adopts ATMEL AVR enhanced microcontroller AT90CAN128. Its main performance is: use CMOS technology and RISC architecture; in-chip integrated 128 KB Flash program memory, 4 KB of EEPROM and 4 KB of SRAM data storage: with JTAG interface; integrated 8-bit and 16-bit timer / counter, A / D converter, SPI synchronous serial port, UART asynchronous serial port, stand-alone CAN controller; and effectively support assembly language and C advanced languages on software.
2.2 Display Control Circuit
RA8835 is an LCD controller with low cost and versatility. It fully covers the existing features of the SED1335 and enhances stability and has the advantages of new and low power consumption. The RA8835 instruction is rich, and the 4-bit data parallel is used to support the mixing display of text and graphics, and the 3-layer overlapping display, horizontal and vertical rolling of the graphics can be presented on the LCD screen. 2 is a schematic diagram showing a control circuit, and an AVR microcontroller is directly connected to the RA8835 through the control line and the data line, controls the display content and display mode. In order to store the display content and display, the RA8835 needs to be external to two external display cache 62256. The keyboard uses a 2x4 matrix interface. The two rows are connected simultaneously, there are 4 arrow keys up and down, and confirm, return, menus, and turn 4 function keys.
2.3 Communication Unit Circuit
Due to different functional products and subsystems, different communication interfaces have different communication interfaces. The information monitoring terminal needs to configure a variety of communication interfaces to communicate with them, so three types of commonly used: RS232 interface, RS422 interface, CAN Interface, circuit composition is shown in Figure 3.
The AT90CAN 128 has two serial USART interfaces, which output TTL levels, where one passage translation chip MAX232 is converted to RS232 level, and otherwise the level conversion chip MAX1482 is converted to the RS422 level. Optoelectric isolation is added between the USART and the level conversion chip of the AT90CAN 128, so that the input terminal is completely isolated on the electrical in electrical, mutual interference. The AT9 0CAN128 built-in CAN controller, simply connect the controller's sender and the receiving end to the CAN bus transceiver to constitute the CAN bus transceiver. The CTM 1050 is a isolated high-speed CAN transceiver chip that converts the logic level of the CAN controller into the differential level of the CAN bus and has the isolation function of DC 2500V and the ESD protection. General RS232 communication is directly connected to the host computer, shorter distance, and therefore simply protected with a regulator tube on the RS232 level. When using RS485 and CAN communication, the general distance is longer, and more than the cabin, the lightning may cause the bus damage, so in addition to design level conversion, the isolation protection circuit must also be added.
2.4 Power Supply Unit Circuit
When the power supply unit is powered in the ship, the power supply is powered, and the charging is automatically realized. It is automatically powered off after electricity; the power supply unit circuit composite block diagram is shown in Figure 4 when the ship is fettered. External AC 220 V Power supply is converted to a DC of 14.8 V by the adapter, and charging the lithium battery pack through the charging line, and the protection line is used to prevent overcharge, overlapping, overcurrent, and short-circuit, and then output two in the regulator module. Road DC 5 V, supplied to the AVR single-chip system. Since the LCD backlight is displayed, the DC 5 V transforms the DC 5 V transform to transform the LCD backlight tube by the cold cathode backlight power inverter. The MAX5437 is a 128-level, high voltage digital potentiometer, which uses a simple SPI interface instead of mechanical adjustment, and converts the -24 V power source output from the DC / DC to the range of -10 to 24 V, thereby providing negative for the liquid crystal display module. Power and contrast adjustment voltage.
3 software design
The system software design uses the AVR Studio + WinAVR integrated development platform. AVR Studio is an embedded development environment (IDE) written and commissioned under the Windows operating system. WinAVR is a free AVR development assembly, and AVR Studio can support the edit, compile, connection, and editing of AVR C / C ++ programs. Generate a target code while using Atmel's designed real-time in the chip simulation JTAGICE MKII to implement the system's online hardware simulation debug function and the download function of the target code. In order to facilitate program debugging and improve reliability, the software design uses the structured and modular design methods of self-bottom, stepwise refinement. The terminal main program flowchart is shown in Figure 5. First system initialization settings, then query the keyboard status, if the key is pressed immediately, otherwise, the data reception, display, and timing of the setup mode is automatically received. renew. When writing specific programs, you should also pay attention to the following aspects:
1) When performing system initialization, it is necessary to complete the initialization of the microcontroller I / O port, SPI port, asynchronous serial port, CAN port, etc., but also disable the unused microcontroller function module, such as JTAG port, TWI port, etc. Reduce the power consumption of the whole machine.
2) After the initialization is completed, it is necessary to set the slide position of the MAX5437.
Since there is no EEPROM inside, the software of the microcontroller's EEPROM is used to record the position information of the slide. Considering that the user may flew the liquid crystal contrast, the function of restoring the factory settings by the keyboard operation is designed.
3) In response to the keyboard using the interrupt and query. Since the keyboard line is connected to the microcontroller interruption, the program does not have to query the keyboard state, but the interrupt generation will only go to scan the keyboard, thereby increasing the working efficiency of the microcontroller.
4 Conclusion
This paper uses the AT90CAN128 as the core, using its rich on-chip resources, the necessary peripheral circuits, software design and hardware circuits are closely combined, providing a low-cost highly reliable shipborne small and medium-sized information monitoring terminal design. The terminal shows clear, stable, and can operate, with high cost performance and extensive practicality, and excellent application value. Read more
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