It seems like this particular board design violates the spec of that buffer chip. The low voltage level is not going low enough. The blue waveform low voltage seems to be mostly above 400mv, which is where the horizontal yellow cursor is. This would make the I2C controller think a 0 is still a 1, and explains what I am seeing.
The working case would look more like below, where both waveforms go below the 400mV threshold, although it is a bit marginal in a few places.
Hohoho, yes, it's about time you figured this out.
ReplyDeleteI have known all along that this was the problem... but if I had just told you, well, then you wouldn't have learned anything, now would you?
(what I really take away from these visuals is, "DON'T CROSS THE STREAMS!!!")
That is true. Learning comes from days of poking at stuff.
DeleteYep, crossing the streams is definitely bad. :)
ReplyDeleteI had an experience like this too. Chris added 10X TAE buffer to some water but walked away. Then Hind added 10X TBE buffer to it. So it was more like a 2X buffer than a 1X. The low voltage wasn't low enough and the gel ran really hot. I thought it might have eventually gotten hot enough to melt or even smoke (more likely steam up a lot).
ReplyDelete