Sensirion SHT1x able to coexist on I2C bus?
Phil Pilgrim (PhiPi)
Posts: 23,514
I've been looking over the documentation for the Sensirion SHT1x relative humidity sensor. It has a two-wire serial protcol that's different from I2C. But what's interesting about it is its start condition: it's equivalent to an I2C START, followed by one clock, and then an I2C STOP. After that, data communication can take place, none of which involves any I2C START or STOP conditions. It would seem, then, that this device could coexist on a bus with I2C devices, since all communication takes place outside of the I2C START/STOP bracketing. What's not clear, however, is what happens between a real I2C START and STOP if there's more than one clock (i.e. normal I2C communication). Even though the SHT1x docs specify one clock pulse in between for its own start condition, it doesn't say what will happen if there's more than one. In other words, would each I2C communication sequence initiate comms with the SHT1x after the STOP? I would guess not, which would make bus sharing with I2C devices possible.
Has anyone tried this?
-Phil
Addendum: This from the Sensirion FAQs:
Post Edited (Phil Pilgrim (PhiPi)) : 9/22/2007 3:36:16 AM GMT
Has anyone tried this?
-Phil
Addendum: This from the Sensirion FAQs:
But this doesn't explain why not, and I don't see anything in the datasheet that would preclude sharing the data line as well.The sensirion.com FAQs said...
5. Is your bi-directional 2-wire interface compatible with I2C ?
No it is not. The difference is in the start/stop sequence (transition start with SHTxx) and how the SHTxx humidity sensor signals the end of a measurement. SHTxx should not share a I2C bus with I2C components. However sharing of the SCK line and using a dedicated DATA line for the SHTxx humidity sensor will work well.
Post Edited (Phil Pilgrim (PhiPi)) : 9/22/2007 3:36:16 AM GMT