UART (Universal Asynchronous Receiver/Transmitter) protocol analysis is a common debugging task in electronic engineering and embedded system development, aimed at capturing, decoding, and verifying UART communication data to ensure the correctness and reliability of data transmission between devices. The following is a detailed analysis of the UART protocol:

1、 UART protocol foundation: the core mechanism of asynchronous communication

Start bit: Low level (0), indicating the start of data transmission, lasting for 1 bit cycle.

Data bits: usually 5-9 bits (commonly 8 bits), transmitted in LSB (low bit) priority order.

Parity bit (optional): odd check, even check, or no check, used to detect single bit errors.

Stop bit: High level (1), lasting for 1-2 bit cycles, indicating the end of data transmission.

Baud rate: The number of bits transmitted per second (such as 9600, 115200), which must be strictly consistent between the sender and receiver.

No clock signal synchronization, relying on the start bit and baud rate to achieve data alignment.

Idle state: The bus remains at a high level (1) and is in this state when there is no data transmission.

2、 The core objective of UART protocol analysis

Verify communication parameters: Confirm whether the baud rate, data bits, checksum, and stop bit settings match (such as setting the sender to 9600-8-N-1 and the receiver to be consistent).

Detecting baud rate deviation (such as an actual baud rate of 9610 instead of 9600) may result in data misalignment.

Capture and decode data: convert the original waveform into a readable format (such as ASCII characters, hexadecimal values).

Frame error: The stop bit is not at a high level (such as being pulled low due to noise interference).

Verification error: The received data does not match the checksum (such as when the sender sets it to even parity and the receiver calculates it as odd).

Overflow error: The receive buffer is full and new data is discarded (common in high-speed communication or processing delay scenarios).

Check if the delay from the falling edge of the starting bit to the first data bit meets the baud rate requirements.

Verify whether the interval between consecutive frames (such as 10ms) meets the device response time requirements.

3、 UART Protocol Analysis Tools and Methods

1. Logic analyzer

Advantage:

-Multi channel synchronous capture (capable of simultaneously monitoring signals such as TX, RX, CTS/RTS, etc.).

-Built in UART decoding engine, directly displaying ASCII characters or hexadecimal data.

-Support triggering conditions (such as capturing a specific string 'ERROR' or a data frame at a specific address).

Operation steps:

-Connect the logic analyzer probe to the TX (transmit) and RX (receive) lines of UART.

-Set the sampling rate (at least 10 times the baud rate, such as 115200 baud rate requiring ≥ 1.152MS/s).

-Configure triggering conditions (such as edge triggering or word triggering "0x41" (ASCII 'A')).

-Capture data and view decoding results, checking for any error flags.

2. Oscilloscope (with UART decoding function)

Advantage:

-Observe the details of the signal waveform, such as the steepness of the falling edge at the starting position and the level of noise.

-Measure signal amplitude (ensure high level ≥ 2.4V, low level ≤ 0.8V, in compliance with TTL standard).

Operation steps:

-Connect the oscilloscope probe to the TX or RX line of UART.

-Enable UART decoding function, set baud rate and data format.

-Trigger capture and observe the waveform, check the timing relationship between the start bit, data bit, and stop bit.