How does i2cdetect work

The first 8 bits of data after the start of an I2C message phase START condition and address sending is actually the 7 bit I2C address of the device to be accessed, along with a bit to indicate if we want to do a Read or Write. The Device being accessed the Slave device , always listens to every address trasmitted on the I2C bus, and when the address matches will ACKnowledge this. This way nothing is trying to drive the bus High at same time as something else is trying to pull it low.

If Low a device has ACKnowledged that the address sent is its address and it is present. If High no device has pulled the line low, so the pullup resistor has pulled the data line High, indicating no device. Having done this for an address i2c detect should be sending a bus message phase STOP condition to abort the tranbsaction, then repeat for next address.

As there are only possible 7 bit addresses th combination is the master , this can be done quickly. Also some addresses are reserved for advanced uses so the scan should be of a lower number than Wed Sep 12, pm Hi techpaul, Thanks for the very prompt and good explanation on how i2cdetect scan works.

Would I be right in saying that not all i2c slave devices respond correctly to a scan. Terms of use of this documentation. Acme Systems srl provided this documentation "as is" without warranty or guarantees of any kind. We not provide any direct support for the Open Source software which can running on our board but, through these pages and forum posts, we provide all of the information required to obtain the sources, install, use and update the Open Source software available on Internet.

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