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Differences And Connections Among SPI, I2C, And UART


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The bus system is undoubtedly one of the essential components of electronic circuits. As a bridge between electronic systems and the external world, the bus system is indispensable. Among them, SPI, I2C, and UART are the three commonly used bus protocols. However, many people believe that they have similar functions and insignificant differences, leading to improper usage and the inability of the system to function properly. Therefore, this article will discuss in detail the differences and connections among these three protocols.

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It consists of three signal lines (Serial Clock - SCLK, Serial Data Out - SDO, Serial Data In - SDI). Multiple SPI devices can be interconnected. The SPI device that provides the serial clock is called the SPI master or host device, while other devices are referred to as SPI slaves. Full-duplex communication can be achieved between master and slave devices, and when multiple slave devices are present, an additional slave select line can be added.


It is a bidirectional, two-wire (SCL, SDA), serial, multi-master interface standard. It features a bus arbitration mechanism and is suitable for close-range, intermittent data communication between devices. In its protocol, data transmission includes the device address of the destination device, allowing for device networking.


UART is an asynchronous serial interface, so it generally has a more complex structure compared to the previous synchronous serial interfaces. It typically consists of a baud rate generator (which generates a baud rate 16 times the transmission rate), a UART receiver, and a UART transmitter. In terms of hardware, it requires two lines, one for transmission and one for reception.

The differences among them are as follows:

Generally speaking, I2C requires fewer lines and has overall more powerful functionality compared to UART and SPI. Therefore, it has a wider range of applications. However, its technical development can be more challenging. This is because I2C requires support for bidirectional I/O and the use of pull-up resistors. It also has weaker interference resistance. As a result, I2C is commonly used for communication between chips on a single board and is rarely employed for long-distance communication. UART requires a fixed baud rate (with equal intervals between two-dimensional data), while SPI is a clocked protocol. Among the three, SPI is the simplest bus system.

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