Decoding I2C data with Flojoy

Using a Tektronix oscilloscope

This is the second in a series on test & measure automation using Flojoy and Tektronix instruments.

See Part 1 on how to characterize a filter with a Bode plot.

Flojoy Introduction

Flojoy is a modern test and measurement (T&M) app that uses Python. Flojoy has the ease of use common with no-code applications. It also offers advanced users the option to create custom Blocks of Python code for specialized applications. Here we show a use case for using Flojoy with Tektronix instruments.

I²C

I²C (Inter-Integrated Circuit, Wiki) is a serial communication bus first used in the 1980s. The biggest advantage is simplicity (2 pins) and the biggest disadvantage is speed (or lack thereof) compared to other bus standards. When testing circuits, serial buses must sometimes be decoded to ensure a device is working as intended. Oscilloscopes are often used for this purpose. Here, we demonstrate how to use Flojoy for no-code decoding of I²C signals.

Figure 1: I²C uses two channels (clock and data) to transfer data.

Setup

The first step is ensuring Flojoy can connect to the oscilloscope. See Part 1 for a guide on how to make a hardware connection in Flojoy. Also ensure your I²C source is turned on and connected correctly to either digital or analog channels on the scope (one for each data and clock).

Next, load the I²C setup app. You can see in Figure 2, the app is made of “MSO2X” blocks. Right click the first block and press “edit block”. For all of the blocks, ensure the instrument selected in the parameters is the correct one. The instrument parameter should be the top one in the parameter menu. Here, the selection is an MSO24 oscilloscope.

Figure 2: Select the correct instrument in the block parameter menu

Next, other parameters must be setup according to your specific needs. For example, turn channels on or off with CHANNEL DISPLAY MSO2X and DIGITAL CHANNELS MSO2X blocks as required. Then, choose the I²C specifics such as number of bits to trigger on and which channels to use as clock and data (with DECODE I2C MSO2X).

Figure 3: Choose how the oscilloscope will trigger

Once the parameters are set, run the setup app to ready the oscilloscope. The SETUP FILE MSO2X block can be used to save all these settings on the oscilloscope for later use.

Running the decoding app

Once the setup app has been run, load the decode I²C app. Ensure the parameters of the decode block matches your requirements and that the correct instrument is selected. Note the SETUP FILE MSO2X block can be inserted between the connection and single trigger blocks to include the setup app in a single block (if you have the settings already saved on the oscilloscope). This app triggers the oscilloscope (once) every time it is run and decodes the resulting I²C message.

Figure 4: The app for decoding I²C data.

Once the app is setup, run it. The resulting decoded message should be displayed (in TEXT VIEW). You can run the app multiple times or put it inside a loop to continuously run it.

Figure 5: Run the I²C decoding app. Note the decoded messages on the laptop and oscilloscope match (except the “h” termination.

Congrats you’ve decoded an I²C message! If you had any difficulties here, or any comments or suggestions please contact us.