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This lesson talks about the bus signal of the LCD backlight screen touch circuit

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There are generally two types of buses for touch screen,

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but only one is used in a single circuit, either the I2C bus or the SPI bus

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Most of the backlight screens use the SPI bus

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Let's take Huawei mobile phones as an example to explain

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Open Xinzhizao intelligent query system

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We find the connector of display and touch

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LCD Interface means display interface

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Most mobile phones now have the same display and touch connector

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TP means touch

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There are four SPI buses here, a chip select signal, a clock signal,

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an output signal and an input signal

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This is the SPI bus for touch

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CS is the chip select signal

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CLK is the bus clock, it needs this clock signal to work

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In fact, MOSI can be regarded as an output signal

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MISO can be viewed as an input signal

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These are the four wires of the SPI bus

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Next we use one of the lines to find the SPI bus

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The 4 lines are connected to one place at the same time, we only need to find one of the lines

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Pin 43 of J1701 is a chip selection signal,

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which is connected in series with a 47 ohm resistor, R1721

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After passing through the resistor, it is named as the chip select signal

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Where does this touch signal lead to?

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Generally it is connected to the CPU

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Copy this signal, paste it into the search box, and click Search

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We found that it leads to the pin AE48 of this chip

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This chip is called U300, model is Hi3680

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It is the CPU of Huawei HiSilicon

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Then we know that this signal leads to the AE48 pin of the CPU

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What about the other three wires?

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The touch clock goes to the pin AD47 of the CPU

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The input signal goes to the pin AE46 of the CPU

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The output signal goes to the pin AD45 of the CPU

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let's sum it up

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The SPI bus is connected in series with a 47 ohm resistor from the touch connector to the CPU

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Ok, this is the SPI bus

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That's all for our lesson