Saleae Logic Analyzer

Summary

The Saleae ("say-lee-ay") Logic Analyzer is a tool used for analyzing data from low voltage logical signals. On EVT, this is one of our most valuable tools for debugging communication between devices for all types of low voltage communication protocols. More information can be found in the Saleae User Guide.

Setup

Before you can use the Saleae, you'll need to download Logic, the software that interfaces with it. This can be downloaded from Saleae's website. There aren't any special steps in the setup, so you should be able to get it running quickly.

Use

To get the Saleae ready for use, first plug it into your computer and open Logic. After a few seconds, your computer should detect the Saleae and connect. Once you computer connects, the LED on the top of the Saleae should light up, indicating you're ready to go.

The next step in setting up is wiring the Saleae to the circuit that is passing the signals you're interested in. Before plugging anything in, start by turning the circuit off. Moving Saleae probes while the circuit is live is almost never helpful and has a good chance of damaging the circuit if you make a mistake. Next, you should take a moment to reconfirm that signal you're working with is safe to read. The exact voltage rating for the Saleae you're using may vary, but if the signal is 5V or less, you should be fine. If the signal is more than 5V, consider using an Oscilloscope instead. If you're not sure what the voltage is, check with a senior firmware member. Once you're certain the circuit is off and the signal is safe to probe, you can begin wiring.

The pins on the Saleae are grouped into pairs, one of which is a signal wire and the other of which is ground (GND). If you're probing multiple signals, with different grounds, you'll need to connect the ground probe for each signal to the appropriate ground. If all the signals you're probing are using the same ground, you can just connect one ground probe. If you're connecting the Saleae to pin headers, it's fairly easy to connect everything by sliding the probes on. If you're trying to probe something without a header, or the header is already in use, you should use the grabber probes to get a connection somewhere on the board. When using this type of probe, be very careful not to short any pins together. If you're unsure, a second pair of eyes, experienced or not, can provide a helpful sanity check.

Once everything is wired up, you should set up your analyzers. The second button under the play button on the right side of the Logic window will open the analyzer tab. In the top right of this tab, you can press the plus button to add analyzers fo I2C, SPI, CAN, UART, and more. When setting these up, make sure you identify which pins are connected to which signals and that you have your configuration parameters set correctly. If the analyzer output doesn't make sense, this should be one of the first things you check, as it is very easy to make a mistake. Note that PWM doesn't require an analyzer because you can just hover over the signal to see the frequency and duty cycle.

After everything is hooked up and your analyzers are set, you should press the play button to start recording data. Then, turn the circuit on, run whatever test you would like, turn the circuit off, and stop the recording. Then, you can scroll back and forth across the data to see what happened. If you want to take another recording without overwriting the previous one, you can press the plus button in the bottom bar to create a new session. If you want to save a recording to look back at later, you can do so with the menus in the top left corner of the window.

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