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In order to improve the display speed of graphic information and get more display effects, the article is based on FG_V1.2 MCU development board. According to the operation timing requirements of OLED12864 display screen, the display system design based on 0.96 inch OLED screen is realized with 51 single chip microcomputer. Actual tests have shown that it has a faster refresh rate and better display than the 12864 LCD module.
OLED (Organic Light EmitTIng Display) display technology is a new generation of flat panel display technology that is more advanced than liquid crystal display technology. It is recognized by the industry as the third-generation display technology that is the most ideal and most promising after LCD and PDP. Compared with liquid crystal display technology, it has ultra-thin, high brightness, wide viewing angle, self-illumination, fast response, strong shock resistance, low power consumption, wide temperature range, flexible display and other features, and has a "dream display". The reputation can be widely used in communications, computers, consumer electronics, industrial applications, commerce, transportation and other fields. In terms of display output, there are currently three main methods, namely: graphics, digital or special symbols. In the embedded field, LEDs, digital tubes and liquid crystal displays are often used. The first two implementations are simple, but the display content is not rich enough. Although the LCD display can display a relatively rich content, its response is slow (afterimages appear) and the brightness is relatively low. OLEDs respond faster, their response speed is more than 1000 times that of liquid crystals, and OLEDs do not require backlights, high brightness, and are superior to LCD displays in terms of power consumption and viewing angle. In view of this, OLED displays are more and more widely used. Applied in everyday life.
This article takes Hongjing's STC89C52 single-chip microcomputer as the control core. The 0.96-inch OLED module provided by Xinyi Electronic Technology is the display output device. The OLED display module driver is written in the Keil environment, and the Hex file is downloaded to the single-chip microcomputer to realize the OLED display. system design.
1 realization principle
The OLD module used in this paper has the same resolution as the 12864LCD, but it has more pixels per unit area. The driver chip of this module is SSD1306Z, which is a COMS chip specially used to drive OLED dot matrix screen, which contains 128 segments and 64 common terminals. In order to be able to write digital information for display to it through an external controller, it provides 8 data pins and 5 control pins externally, and provides four kinds of bus interfaces to the user. The OLED module used in this paper can implement SPI and IIC bus interface modes, and the default is SPI mode. In SPI mode, only the lower 2 bits of the data pin and the CS#, D/C# and RES# of the control pin are interfaced with the microcontroller. In order to make the OLED rich in display effect and flexible and easy to operate, the SSD1306Z provides users with a rich set of operating instructions, and also provides users with 128x64-bit GDDRAM (Graphic Display Data RAM). Since the OLED used does not have a font, whether it is displaying graphics or displaying Chinese characters, it needs to be encoded by the modulo software, and then the corresponding encoding is written into the corresponding CDDRAM according to the determined address mode according to the SPI protocol. The coding principle is shown in Figure 1. Figure 1 shows the character 'A' in the 16*8 encoding format. Since 8 acts as a page, it occupies 2 pages and the width occupies 8 columns. Each square in Figure 1 represents a bit, set to 1 if displayed, and vice versa. When sending data to GDDRAM, first determine the address mode and address of the memory required by the operation, and then write the code of the second page of 'A', and then write the code of the third page, then the code can be written. Into the operation. The code corresponding to Figure 1 is 0x00, 0x00, 0xe0, 0x 9c, 0xf0, 0x80, 0x00, 0x00, 0x08, 0x0f, 0x08, 0x00, 0x00, 0x0b, 0xoe, 0x08, with the high bit being lower and the lower bit being upper. In the same way, the encoding of any Chinese character can be obtained.
Figure 1: OLED character encoding
2 timing analysis
The operation timing provides the correct tempo for the reliable operation of the IC chip. Therefore, the correct operation timing will directly affect the working state of the chip. The default working mode of the OLED module in this paper is 4-wire SPI, and its operation timing is shown in Figure 2. The upper part of Fig. 2 is the timing corresponding to the operation of one bit, and the lower part is the timing corresponding to the operation of one byte. It can be seen from Fig. 2 that when one byte is transmitted, the highest bit of the byte is sent first, and the lowest bit is sent last.
Figure 2: 4-wire SPI operation timing diagram
In Figure 2, CS# is the OLED chip select signal line, which is active low. After the chip is valid, it can be determined by whether the command write operation or data write operation is performed by pulling low or pulling D/C#. Before the SCLK is pulled high, the D/C# signal is established. The setup time is tAS, SDIN is active at SCLK low level, and the data is read at the rising edge of SCLK. The data hold time is tDHW, after which data exchange can occur. The secondary data is read in preparation. The specific timing characteristics in Figure 2 are shown in Table 1.
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