Greets All,
I am a new guy to using a scope and am learning more everyday, especially here. I am sure my terminology is not correct at all so please bare with me.
I ran into a small issue where I2C logic transitions from one channel seem to influence the waveform on the second channel. It seems to be both ways, where the clock transitions seem to effect the data waveform, and vise versa. With all the tutorials, both HTML and Video, the waveforms shown seem to be a bit cleaner than what I am getting, and I just wanted to know why it is happening so I can attempt to correct it. Ground issues, using short jumpers to connect the probes, maybe actually a circuit issue like not enough current on the 3.3vdc rail, incorrect power decoupling capacitors, etc.
The platform I am connected to IS on a bread board. Before I start ripping that apart and start connecting wires directly to the gear, I wanted to ask this here. I am using short jumper wires to connect to the test points because I do not want to short anything on the modules. Maybe that is just a probe trust issue. They are retractable spring hook types set at 10x. I have two pulled screen shot files I have included thanks to a wonderful linux python script and the ethernet connection I have with the scope, and SCPI. GOD I LOVE THAT FEATURE!!! Sorry, had to share that. No more smart phone pics of the scope's screen anymore for me! YAY!
More about the circuit...
I am testing slave I2C programming on a blue pill STM32F103C8T6 with a Bus Pirate V3.6. I have the blue pill board and an accelerometer module (GY 80 -
ADXL345, MC5883L, L3G4200D, BMP085) connected to the same bus. Both modules addresses are responding to an I2C address search function from the Bus Pirate as expected. Resistor pull ups to 3.3v are applied through the bus pirate and are enabled. I will take a pic of that set up for this post and include it. There is a side question here... what is the best way to apply my scope's probes? As far as the probes ground connection and the probe's main connection?
Here is two screen shots of the waveform that I get. Noticed the little dips and spikes in one waveform when the other transitions. The second shot is zoomed in to show more detail of the anomaly. The last image is my setup. All images are attached. I did not know how to insert an image into the post. Sorry.
Thank you for your time and I appreciate anything that could be elaborated on here.