Don't just memorize the manual! Being able to spot correct or incorrect SPI waveforms at a glance is a fundamental skill in embedded systems.

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Don't just memorize the manual! Being able to spot correct or incorrect SPI waveforms at a glance is a fundamental skill in embedded systems. [Copy link]

A friend configured SPI mode 3 according to the chip manual, but the data captured was always incorrect.

In fact, you can make a judgment directly by looking at the waveform.

There is a fundamental principle in communication:

At the sampling time, the data must be stable and cannot change abruptly!

In his waveform, the sampling point data is changing rapidly, so the mode must be misconfigured.

Inferring from the waveform:

- Clock idle is high level → CPOL=1

- Data is sampled at the first edge with CPHA = 0 (because MISO and MOSI remain stable at the first edge, but change at the second edge).

The correct mode is: Mode 2 (CPOL=1, CPHA=0)

Many people who learn embedded systems start with STM32, but their basic knowledge is terrible.

You must thoroughly understand UART, I2C, and SPI: be able to memorize them, draw them, and understand them just by looking at the waveforms.

An expert can pinpoint a problem in a minute, while a novice takes half an hour; that's where the efficiency difference comes from.

Learn the 51 microcontroller first and solidify your timing fundamentals; then you'll learn everything else much faster.

This article is quoted from Jinshatan Electronic Classroom.

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Another way is through practice; by frequently observing waveforms, you can immediately identify the problem.

秦天qintian0303

Logic analyzer, analyzes without you having to look at it.

卓然尘世间

Qintian0303 posted on 2026-3-19 15:16 Logic analyzer, it analyzes directly without you having to look at it.

Good method, convenient and accurate.