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iPhone mobile phone commonly used bus

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In this video, we mainly explain the SPI bus

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The SPI bus is a full-duplex synchronous serial bus developed by Motorola.

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For communication between microcontrollers and external devices

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SPI works in master-slave mode

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Generally there is one master device and one or more slave devices

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The CPU is equivalent to the master device

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It is connected to audio, hard disk, touch screen and fingerprint through SPI bus

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These devices are slave devices

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The SPI bus consists of four wires

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In some circuits, three wires will work fine

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The main signals of this line are

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MOSI, master output slave input

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MISO, master input slave output

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SCLK is the clock signal, generated by the master device

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cs Chip selection is sent by the master device, which device is used to control the communication

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There are many devices used in the iPhone mobile phone

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For example, the main audio to the CPU, and the hard disk to the CPU also have an SPI bus

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The touch screen to the CPU is also through the SPI bus

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The fingerprint to the CPU is also transmitted through the SPI bus

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Is there anything listed in the frame diagram?

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e.g. compass, gyroscope, barometric pressure sensor

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These peripherals also transmit data through the SPI bus

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If there is a problem with the SPI bus, the corresponding function will not be available.

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Below we take the iPhone 8P Qualcomm motherboard as an example to check the SPI bus from the touch screen to the CPU

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We first find the display touch connection socket on the annotation diagram

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Then go to the drawing to search for the connection seat

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After finding the connecting seat, we can see that there are many English words on both sides of the connecting seat

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As long as the SPI is marked, it belongs to the SPI bus

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If TOUCH is marked, it means it is the SPI bus of the touch screen

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SPI TOUCH TO AP MISO refers to data output

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The SPI AP TO Touch CS signal is a signal for the CPU to select the touch screen when communicating with the touch screen

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MOSI stands for Data In

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SPI AP TO TOUCH SCLK is the SPI bus clock from the CPU to the touch screen

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iPhone 8 p touch screen has 4 SPI signals

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Then the CPU to the fingerprint is also the SPI bus

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But the bus uses three lines, the search method is the same as above

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After finding the connecting seat, we can see the English of the line identification

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The one that identifies SPI represents the SPI bus

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Among them, 15 feet, 17 feet, and 21 feet

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These English names all contain spi

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That means that these three lines belong to the SPI bus from the fingerprint to the CPU

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Among other pins, we can see that there is no SPI mark

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That means the SPI of the fingerprint only uses three lines

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That bus is connected to the CPU

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We can check the connection through the bitmap

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In the bitmap, each bus passes through one or two fuse resistors

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Then connect to the cpu

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The clock of the SPI bus passes through two fuse resistors to the cpu

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data input from the bus

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The data input is connected to the CPU through a safety inductor FL5840

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21 pin data output

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The signal is connected to the cpu after passing through the R5844 fuse resistor

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It can be clearly seen from the diagram we just checked

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The SPI bus of the fingerprint is connected to the CPU

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After the SPI bus is damaged, the corresponding functions will be unavailable

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If the SPI bus of the touch screen is damaged, it will cause no touch

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If the SPI bus of the fingerprint is damaged, the fingerprint function will be unavailable

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That's all for this video