I2C Bus Sniffer

[John Michel]

Hello,

Is it possible to use the digital discovery as an I2C bus sniffer? Meaning I can pass data through the digital discover that is flowing to and from my I2C devices and have that data displayed in the I2C protocol analyzer.  If so, can you point me to some instructions on how to do that.  So far I've only seen how to hook up one device and analyze the data from just it.

Many thanks in advance.

[JColvin]

Hi @John Michel,

If you want to view the sniff some external I2C bus data flowing through a larger external daisy chain, I would use the Logic Analyzer to add (via the green plus button underneath the "Single"/"Run" buttons to add a pair of pins for the SCL and SDA lines, which you would then connect to the existing daisy chain. You can then just have the device run to capture data, or if you want to capture specific material you can set up a Protocol trigger to look for a particular address and data byte combination.

If you need to adjust any of the pins to have pull-up resistors, you can do that for each individual pin within the Supplies tool, or through the Device Options which is accessible either via the 100 MHz dropdown at the bottom of the screen or within the DIOs tab in the Settings -> Options at the top of WaveForms.

The challenge with using the Logic Analyzer for I2C is that I2C devices tend to a have a relatively large amount of downtime between transactions, so you'll end up using a comparatively large timebase to capture the entire sequence and then be using the arrow buttons on the plot to have the screen scroll for you between events.

Within the Protocol Analyzer instrument, you also use the I2C option to sniff all I2C traffic or choose to only receive data sent to a particular address (via the filter checkbox), as well as having the option to have the Digital Discovery as a controller to send your own traffic.

The catch then becomes that you are more limited in your trigger options as well as being limited to only working with a single protocol at a time, whereas using the Logic Analyzer directly, you can add any number of different protocols (until you run out of pins on the Digital Discovery anyways).

As always, additional information about the various settings is available in-app within the Help tab.

Let me know if you have any questions.

Thanks,
JColvin