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This lesson talks about the touch circuit of the OLED screen

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Let's look at the lines of the bus

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The touch bus generally uses I2C bus or SPI bus

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Let's take the OLED screen of Xiaomi 9 Pro as an example

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Open Xinzhizao and find the display and touch connector J6400

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Find the bus of the touch circuit

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TS is for touch

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There is an I2C bus here

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These two lines are the touch data transmission buses

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One is SCL, serial clock, one is SDA, data

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One on the bus is a clock signal and the other is a data signal,

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which constitute a communication bus

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This clock goes to pin 12 of the touch connector

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This data goes to pin 10 of the touch connector

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This bus is usually connected to the CPU, this is a rule,

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everyone should remember this

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Next, let's see which pins of the CPU it leads to

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Both of them go to the same place at the same time, we only need to check one of the lines

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Double click on this clock signal

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We found that the clock goes to pin L1 of this chip,

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and the data goes to the K1 pin of this chip

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What kind of chip is this chip?

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Its location number is U3100 and its model number is SM8150

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This is the Qualcomm CPU

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In other words, the I2C bus of this touch is connected to the touch connector and the CPU at the same time

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Let's double-click to continue to find its line

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The pull-up circuit on its line is at this position

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TP I2C means this is the touch I2C bus

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The right end of the I2C bus is the power supply

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Here are two 2.2 k resistors

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The end of the pull-up is powered by 1.8V

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The other end of the resistor must also have a voltage of 1.8 V

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This is the I2C bus line for the touch

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Let's sum up, this bus leads to the connector and CPU,

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the connector is J6400, and the CPU is U3100

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That's all for this lesson