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AN2687 Datasheet(PDF) 7 Page - STMicroelectronics |
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AN2687 Datasheet(HTML) 7 Page - STMicroelectronics |
7 / 22 page AN2687 LCD drive signals Doc ID 14296 Rev 1 7/22 2 LCD drive signals 2.1 Quadruplex LCD drive In a quadruplex LCD drive, four backplanes (common lines) are used. Each LCD pin is connected to four LCD segments, whose other side is connected to one of the four backplanes (refer to Figure 3). Thus, only (S/4)+4 MCU pins are necessary to drive an LCD with S segments. For example, to drive an LCD with 128 segments (32 × 4), only 36 I/O ports are required (32 I/O ports to drive the segments, 4 I/O ports to drive the backplanes). Three different voltage levels have to be generated on the common lines: 0, VDD/2, VDD. The Segment line voltage levels are 0 and VDD only. The LCD segment is inactive if the RMS voltage is below the LCD threshold voltage and is active if the LCD RMS voltage is above the threshold. The intermediate voltage VDD/2 is only required for backplane voltages. The MCU I/O pins selected as backplanes are set by software to output mode for 0 or VDD levels and to the high-impedance input mode for VDD/2. The VDD/2 voltage is determined by two resistors of equal value, externally connected to the I/O pins as shown in Figure 5. When one backplane or COM is active, the other ones are neutralized by applying VDD/2 to them. Figure 3. Basic LCD segment connection in quadruplexed mode S11 S1 COM1 ai14762 S2 S3 COM2 S14 COM3 COM4 S12 S13 |
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Descripción similar - AN2687 |
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