Can I run I2C in loopback on Analog Discovery (old black model) with protocol/logic analyzer ?

[varunnagpaal]

I tried running both I2C spy and I2C master simultaneously on different DIO pins and connect them in a loopback with pullup resistors. But it isn't working.

For example:

I2C master: DIO[0] as SCLK output, DIO[1] as bidirectional SDA

I2C spy: DIO[2] as SCLK input, DIO[3] as bidirectional SDA

I attached pull up resistors (2.144K) to the SDA and SCLK lines with VDD=3.3V DC which I generate using waveform generator.

I activate I2C spy and then run I2C master. I tried this but it doesn't seem to work. It gets stuck on a window "Transferring data" but never ends.

When I click cancel, it shows "Error!" in the I2C master window. Is their anyway I could possible do I2C loopback with protocol analyzer/logic analyzer  ?

[attila]

Hi @varunnagpaal

In this setup there is no slave to acknowledge but it should work like this:

[varunnagpaal]

So I made DIO[0] and DIO[1] as SCL and SCK for both I2C Master and I2C SPY.

I first click "Receive" in the I2C SPY window:

 

And then I click "Write" button in the I2C Master:

 

But I dont see any capture on I2C SPY:

Not sure why this isn't working.

[attila]

Hi @varunnagpaal

Make sure the wiring is correct and the devices use common ground.
Make sure the pullup voltage is correct, 3.3V or at least above 1.5V

I managed to reproduce the "Transferring data" hold by setting the pullup to 1.5V 
This because at this level it is in hysteresis domain of the 3.3V logic. After the master releases the low drive it will not go up to logic high.

 

Edited November 12, 2021 by attila