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AN2687 Datasheet(PDF) 8 Page - STMicroelectronics

No. de Pieza. AN2687
Descripción  STM8S20xxx LCD software driver
Descarga  22 Pages
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Fabricante  STMICROELECTRONICS [STMicroelectronics]
Página de inicio  http://www.st.com
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AN2687 Datasheet(HTML) 8 Page - STMicroelectronics

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LCD drive signals
AN2687
8/22
Doc ID 14296 Rev 1
Figure 4.
LCD timing diagram for quadruplex mode
2.1.1
LCD mean voltage calculation
The LCD mean voltage must be very close to zero to guarantee long life to the LCD. The
LCD mean voltage for On and Off periods can be calculated as shown below:
Vmean(On) = 1/8 Vseg + 1/8 (–VCOM) + 3(Vseg – Vr/2) + 3(–Vr/2)
(1)
Vmean(Off) = 3(Vseg/2) + 3(–Vr/2)
(2)
Vmean(On) and Vmean(Off) assume identical periods for each phase.
Equating equations (1) & (2) to zero, that is putting Vmean(On) = 0 and Vmean(Off) = 0,
gives:
Vseg = VCOM = Vr = VDD, where:
VCOM is the maximum voltage on the COM line
Vr/2 is the voltage in the middle of the resistor bridge, applied on the COM line
Vseg is the maximum voltage on the Segx line
VDD is the microcontroller power supply
COM1
ai15954
VCOM
+VDD/2
COM2
Segx_1 On
Segx_2 Off
Segx_3 On
Segx_4 Off
Vseg – VCOM
Vseg – VCOM1
Vseg – VCOM4
T/8
T/4
T/2
3T/4
T
COM3
COM4
Vsegx
Control
period
Single-frame period
LCD
COM1
COM2
COM3
COM4
SEG1


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