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Serial Communication

UART, SPI and I2C are the most common serial protocols between a microcontroller and external devices. UART is asynchronous with no shared clock and uses start and stop bits; SPI is synchronous with a shared clock and no start/stop bits; I2C uses just two lines with open-drain outputs and requires pull-up resistors.

\text{SPI bytes/s}=\dfrac{f_{SCK}}{8}

throughput for SPI (no start/stop bits)

Symbols

f_{SCK}

clock frequency of the SPI bus

Example

SPI clock $1$ MHz:

Throughput $=10^6/8=125\,000$ bytes/s.

UART has start and stop bits, SPI and I2C normally do not – count the right number of bits per transfer.

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