ARM7 microprocessor-based Chinese liquid crystal display technology
LCD liquid crystal display as a low power consumption, small size, the display without radiation, in recent years is widely used in a wide range of embedded electronic products, LCD can be divided into Dan-style, character and dot-matrix Type three, of which Dan and character-type LCD can only be used for character-type LCD and a simple digital display, can not satisfy the graphics curve and show that the requirements of Chinese characters, and dot-matrix LCD can display characters, numbers, can also display the kinds of graphics, curve and Chinese characters and can scroll the screen up and down about animated features, district open window, turned around, flashing and other functions, uses a wide range of liquid crystal display to simplify circuit design and applications, manufacturers will usually liquid crystal display unit , display controller, display memory and display driver circuits, such as the assembly together, make LCD Module LCD Module (LCM) . LCM provides the standard external data and control interface and control commands to ATM12864C this article as an example, drive with ST7920 control of the liquid crystal display module and the Philips company's ARM7 microcontroller LPC2214 interface design and programming methods, and details on this basis LCD display in the continuous rolling of the Chinese menu and select menu items displayed on the anti-white design methodology, and discuss how to solve the Chinese characters that appear in the process show that the problem garbled.
2 Hardware Implementation
ATM12864C Jinpeng Electronics Co., Ltd. Guangdong Chinese production of liquid crystal display module, which used liquid crystal display module of the control matrix Chinese font driver ST7920, his 8192 containing 16 × 16 dot matrix of the GB Simplified Chinese characters and 126 16 × 8 character dot matrix symbols in English. Entered by the user code or GB code ASCII text display can be realized. Fit showed eight Chinese characters × 4 lines, and also to provide 64 × 256 points, graphics RAM (GDRAM), can be mixed with text display, but also have a font containing RAM (CGRAM), the provision of programmable functions defined , ATM12864C external interface signals are: 8-bit data bus D0-D8; register select signal R / S, when R / S is high, the control data register, R / S is low, the control instruction register, read and write signals R / W, R / W for the power normal time, when low-level write enable signal E, the effective falling edge, ATM12864C timing of the write operation in Figure 1 (b) below, in addition to sequential read R / W signal is high, the other with the same timing write operations .
Philips Introduces LPC2214 is based on a support of a real-time simulation and tracking the 32-bit ARM7TDMI-S CPU micro-controller, frequency up to 60MHz, with a 256KB high-speed chip embedded flash memory and four 32-bit wide external memory interface, is a low-power, high performance, small package, microcontrollers, LPC2214 external memory access time series in Figure 1 (a) as shown in .
Microcontroller in order to save the general I / O port resources and the preparation of the simplified procedure, LPC2214 through data bus and control signals directly control the external memory access to the form of liquid crystal display module, in this way for some I / O port resource complex systems have a more important significance, because the data access timing STA7920 and LTC2214 timing of memory access is very different, as shown in Figure 1. LPC2214 and liquid crystal display module interface circuit design, the key is how to design reasonable, the LPC2214 and the memory access timing of the visit the ST7920 with the right timing.
LPC2214 and liquid crystal display module of the interface circuit shown in Figure 2. LPC2214 controlled through low LCM address A1 of the R / S signal, to select the current control register through the WE signal to the LPC2214 was appropriate as the LCM after delay of the R / W signal control data bus on the way to the data stream. And LCM to enable the signal E from the time LPC22414 signal OE, write signal WE and memory controller chip select signal CS1 to produce synthetic, have a read and write signals in the R / W signal of the circuit, the resistor R and capacitor c choice is the key, according to LPC2214 and ST7920 Electrical characteristics (see the specific literature [1,2]) and debug the results of the election of the ideal values: R check 1KΩ, C++ check 12PF, in order to achieve low-power, LCM backlight through a common I / O port to control, when in response to external keys, the backlight lit, or back out.
LCM-chip as a result of the election by the CS1 control signal, that is, the use of LPC2214 external memory interface Bank1 address space, while the R / S control signal from the A1, so the operation of LCM as follows:
Enter the address of the command: 0x81000000
Data Manipulation Address: 0x81000002
3 software Design
In with the LCD screen displayprogram design process, the Chinese menu display and the scroll menu choice is the key to anti-white, this article selected liquid crystal display module can display 4 lines, each line shows the eight Chinese characters. When the menu item to display more than four hours, the need for scroll display. In this paper, a human-computer interaction design and friendly menu operation, the program's basic idea: to open up in memory of a show that was 4 × 16 array of two-dimensional character of the display buffer, to be shown a list of menu items are stored in another a two-dimensional array, by changing the display function LCM_Show () parameters, convenient and flexible menu shows a list of menu items specified, assume it to be displayed in Figure 3 (a) of the 5 menu, the default display of the focus in the first and his party, that is, to the first line of the menu item highlighted, when press the "down" key, indicating the focus of his party down. When the focus of the next move when the last line of liquid crystal display, in Figure 3 (b) below, at this time and then "down" key, scroll up the screen, in Figure 3 (c) below, continue to press the "next shift "key, the display continues to scroll up to the cycle show in the list menu 5 menu, shown in Figure 3 (d) below and click" Move "button, the same operation.
This paper shows that function LCM_Show () and anti-white display function LCM_ShowInvert () to achieve continuous rolling, as mentioned above shows that the menu functions and focus of anti-white display. Specific code is as follows:
Chinese characters in the show, the display of Chinese characters and is often mixed ASCII code, as the Chinese character is composed by two bytes, ASCII code is a byte, if the display content of the ASCII number of the number is odd, ASCII Code behind the display of Chinese characters will appear the phenomenon of garbled.
In response to this phenomenon, this paper shows that the pre-formatted to display the contents of the method, the basic idea is: the number of consecutive single ASCII character code followed by a space, so that shows the contents of the ASCII code for characters to maintain two - number, this method has a very good solution to garbled characters at the time of the phenomenon shows. Program flow shown in Figure 4.
In this paper, on the ARM7 microcontrollers LPC2214 and drive with ST7920 control of the liquid crystal display module timing study visit on the basis of the design of the interface circuit between them, the interface circuit without increasing the general I / O, the direct use of the external LPC2214 memory access is simple and convenient form of liquid crystal display control module, saving the general I / O port, but also makes the procedure more convenient to prepare, but also gives the Chinese menu display and menu item Scroll to highlight the procedure of choice, and the process for displaying the phenomenon of the distortion of the discussion, given solutions and the program flow. ARM-based microcontrollers for embedded systems with the display of Chinese characters display system has an effective solution.
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