Hannah I2C power-up fail

Hardware
1

I’ve got a circuit design identical to the Hannah IMP --> GPIO expander (SX1509) configuration. Every once in a while I’ll notice an I2C failure upon power up (either with my design or with the Hannah). I’ll typically just do a power cycle (IMP out - IMP in), then all is well … I2C now works fine. (This is just a very low level infrequent problem at this point … everything typically works fine).

I think I recall reading about this somewhere on the devwiki or forums a while back, but just can’t seem to locate it. If I remember correctly, I believe it was some sort of IMP / GPIO power up sequence issue. I had some time so was going to look into it, but I just first wanted to review what was known about this.

I’d appreciate if anyone could point me in the right direction.

Thanks,
Larry

2

Do you have a pullup on the SX1509’s RESET_N pin? This is required, as I remember.

3

Hi Hugo - yes, I’ve got the 100k pullup on the NRESET pin … as mentioned, I pretty much just copied this portion of the circuit from the Hannah … and I’ve observed this behavior (again, very infrequently) from both circuits. I’ll just see repeated I2C r/w fails until I mechanically cycle the Imp (i.e. power). I thought I saw some comment related to this way, way back … but I can’t recall. It seems to me like some sort of possible IMP/GPIO power on timing issue, but I’m just speculating. (Again, not a really big deal at all, just one of those little quirks I’m trying to get a handle on).

Thanks,
Larry

4

Shouldn’t be a power on issue, we’re very careful about cleanliness of pin configuration transitions. What pins are you using for i2c?

5

I’ve been running I2C_89 Hugo. Yes, it may not be related to power on at all … I just got on that line of thinking based on what I thought I had come across previously related to this on the forum or devwiki.

We can probably put this discussion on hold until I collect a bit more information. Since it’s something I encounter very infrequently/intermittently, it’s been difficult to re-create … I’ll do some more investigating to see if I can pinpoint situations where I’ve seen this. One observation is that I’ll typically see the I2C fail right when I’m trying to bring a new Impee/Imp on line, or switching an Imp to a different Impee … but then I’ll cycle power and the problem is gone. Don’t take this as too solid right now though, I’ll work on it some more and report back.

Thanks again,
Larry