Serial Communication: UART, I²C and SPI

Electronics and Embedded Systems · CHAPTER 5 / 5

Level: introductory undergraduate · Study session: 15–20 minutes including practice.

Learning outcome: Choose a bus using wiring, addressing and timing requirements.

Before you begin: Complete earlier chapters in this discipline; revise algebra and units as needed.

1. Understand the idea

UART is asynchronous and commonly point-to-point. I²C uses addressed devices on shared clock and data lines with pull-ups. SPI uses a clock and device selection with separate data directions in a common arrangement. Voltage compatibility, cable length, clock rate and device timing matter more than protocol popularity.

2. Write the model

UART 8N1: 10 transmitted bits per data byte

Define the symbols from the worked case before substituting values. Keep units consistent, record the assumptions and round only after the calculation.

3. Follow a worked example

At 9600 bit/s with 8N1 framing, an ideal continuous stream carries at most 960 data bytes/s. Sending 100 bytes takes approximately 0.104 s before software delays or protocol overhead.

4. Explore the model

Figure: calculated teaching cases; straight segments connect sampled points, not experimental observations. Read exact values below.

Illustrative scenario sweep — synthetic educational data
Baud (bit/s)	8N1 payload ceiling (bytes/s)	100-byte time (s)
9600	960	0.104167
19200	1920	0.052083
115200	11520	0.008681

Sweep baud and observe ideal transfer duration. Keep framing fixed so the comparison is fair.

5. Reproduce it yourself

Copy the input cases into Excel or a notebook and name each quantity and unit.
Recalculate each result from the stated equation or rule. For qualitative cases, explain the state or partition decision instead.
Change one input, predict the direction of change, then calculate again.
Write one sentence explaining where the model stops being valid.

6. Check your understanding

Why is 9600 baud not 9600 payload bytes per second?

Reveal the answer and check your work

Each 8N1 data byte occupies 10 bit periods.

Compare your result, units and reasoning. If they differ, return to the equation and test the worked case first.

7. Common mistake

Do not connect incompatible logic voltage levels directly.

Further study and academic note

Explore the discipline reference and further learning resources. This is an original IIMEEE introductory teaching note with synthetic examples; it is not a peer-reviewed research result or a professional design specification. Figures were constructed from the listed teaching cases. Resource links support further study and do not imply endorsement.