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iPhone touch circuit repairing

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This video mainly explains the working principle of the iPhone XR and iPhone 11 touch circuit

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The working principles of these two models are basically the same,

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only the individual signal marks are different

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The first step of the working principle, when the trigger is turned on,

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the main power supply will output more than 30 channels of power supply

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The 1.8V power supply will provide the working voltage for the touch screen

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Step 2, after triggering the boot, the CPU is in normal working condition,

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and it will read the touch screen through the I2C bus

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It is mainly to read the information of the display memory chip on the touch screen

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to identify whether the screen is the original screen

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Step 3, when starting to the touch circuit,

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the main power supply sends a 32KHz clock signal to the touch screen

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Step 4, when the touch circuit is started, the CPU sends a reset signal for the touch screen

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Step 5, after the touch screen has power supply, clock signal and reset signal,

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the CPU will detect the touch screen through the SPI bus

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Step 6, after the CPU detects the touch screen,

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it will let the display power supply provide 5.1V power supply to the touch screen

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Step 7, after the CPU has 1.8V, 5.1V power supplies, the clock signal and the reset signal,

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the touch screen will send an interrupt signal to the CPU

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Step 8, after the CPU receives the interrupt signal,

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it will send touch data to the touch screen through the SPI bus

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Then the touch screen can work normally

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These are the main working conditions of the touch screen

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The touch screen also has some other detection signals

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MANY_SCAN is the forced synchronization signal sent from the touch screen to the main power supply,

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display power supply, or other power supplies

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TOUCH_CTS is the data clearing signal

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When the touch screen is not working,

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it will send this signal to the CPU to clear useless touch data

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AP_TO_TOUCH_SCAN is the clock detection signal sent by the CPU to the touch screen

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When working normally, the CPU will check whether the touch clock is normal from time to time

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The UART bus is an asynchronous transceiver bus, mainly used to transmit data for other signals in the touch circuit

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For example, the 3D touch function will transmit data through the UART bus

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When troubleshooting no touch faults, we need to measure all touch signals in the circuit diagram

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If one signal is abnormal, it will cause no touch failure

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Ok, that's all for this video