Electronics Design

Week 06

Logic Analyzer and UART Signal Measurement

What is a Logic Analyzer?

A logic analyzer is an instrument used to capture, display, and measure multiple electronic signals simultaneously in a digital circuit. It allows us to observe the timing relationship between different digital signals and is especially useful for analyzing communication protocols such as I2C, SPI, and Serial/UART. For this reason, it is one of the most useful tools for debugging digital circuits and communication systems.

Reference: Saleae - What Is a Logic Analyzer?

For this assignment, we used an 8-channel USB logic analyzer with a Mini USB cable and jumper wires. The model used was the LA-24MHz-8CH, compatible with the Saleae driver.

8-channel USB logic analyzer with Mini USB cable and jumper wires
8-channel USB logic analyzer used for the test.

In the Fab Lab, we were provided with a board based on the XIAO RP2040. Using this board, we generated a digital output on pin D0 and a serial communication signal using pins D1 (TX) and D2 (RX).

XIAO RP2040 mounted on a red development board
XIAO RP2040 board used to generate the test signals.

Wiring

The pins were connected as shown below:

XIAO RP2040 Logic Analyzer
D0 CH1
D1 CH2
GND GND
XIAO RP2040 board connected to the USB logic analyzer
Connection between the XIAO RP2040 board and the logic analyzer.

Arduino Code

In Arduino IDE, we wrote the following code for the XIAO RP2040. The program generates a digital pulse on pin D0 and sends the message FabAcademy 2026 through pin D1 using a software serial port. 

#include <SoftwareSerial.h>

						#define pinOut D0 // Digital output

						SoftwareSerial mySerialPort(D2, D1); // RX, TX

						void setup() {
						Serial.begin(9600);
						mySerialPort.begin(9600);
						pinMode(pinOut, OUTPUT);
						}

						void loop() {
						mySerialPort.write("FabAcademy 2026"); // Sending a message

						// Generating a digital pulse
						digitalWrite(pinOut, HIGH);
						delay(1000);
						digitalWrite(pinOut, LOW);
						delay(1000);
						}

PulseView Configuration

We installed PulseView for Windows from the following link: https://sigrok.org/wiki/Downloads.

After connecting the USB logic analyzer, PulseView automatically detected the device as Saleae Logic.

The capture settings were configured as follows:

  • Samples: 100K samples
  • Frequency: 50 kHz

Then, we started the acquisition by pressing the Run button and zoomed in to analyze the captured signals.

PulseView capture showing a digital pulse and serial signal
Initial capture in PulseView after zooming in on the signals.

Signal Analysis

In channel 0, we could observe the digital pulse generated by pin D0. We could also observe the serial message transmitted through pin D1.

To decode the message generated by the serial port, we added a protocol decoder from the toolbar and selected the UART protocol.

PulseView interface with UART decoder added
Adding the UART protocol decoder in PulseView.

To display the message in ASCII format, we configured the UART decoder by double-clicking on the UART channel and setting the following parameters:

  • TX (UART transmit line): D1
  • Baud rate: 9600
  • Data format: ASCII
UART decoder configured in PulseView showing ASCII data
UART decoder configuration and ASCII message visualization.

Conclusion

With this test, we confirmed that the logic analyzer can capture both a digital pulse and a UART serial signal generated by the XIAO RP2040. PulseView allowed us to visualize the timing of the signals and decode the serial message successfully using the UART protocol decoder.

Working
Working