Agilent I2C decode on MSO6 and 7k series scopes

[wreeve]

I’ve a MSO7054B which does sterling service usually…. however I can’t seem to get I2C decode working! Here is what I get on a valid I2C exchange. The decode doesn’t work! UART and SPI decode work fine. Must be something simple? All you have to do (I think!) is set up the SDA and SCL channels and the number of bits in the address (7).
It is triggering on the “START” by the way so it notices the start condition as a trigger! This is a valid exchange btw; works fine.
Any ideas?

[nctnico]

Did you set the threshold levels? Settings these is a bit tricky on this scope! You have to go into the signal setting menu and press the button for the signal. Doing that allows to set the threshold for the signal with the trigger level knob.

[Howardlong]

Following on from nctnico's advice, are you sure clock and data are the right way around? It looks like it may be continually seeing start states as the bus decode is switching mid-byte.

Edit: I am sure nctnico is right, your SCL trigger level on channel 1 is at ground for example: you adjust the thresholds by adjusting thr trigger level when using analogue channels for I2C decode when selecting the channel for SCL, and then the same when you select the SDA channel.

[wreeve]

Thanks guys; pushing the level button a few times finally got it to set at 50% and as if by magic decode worked. I was confused as the waveform appeared to be triggering OK but the level wasn't acceptable to the I2C decoder! Thanks again.

[Howardlong]

Bob's your uncle!

[Smokey]

Bob's your uncle!

Not true... Not true at all. Lets stick to the facts!