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In the SMBus spec it says:

The I²C specifications do not require that a device always acknowledge its own address. This can confuse a system controller. If a device does not acknowledge its own address how does the system controller know if it is because the device is busy, has failed, or has been removed?

This sounds a lot like blackening I2C, and I'm not used to see this kind of language in a spec.

Besides, I think SMBus is lying here. In I2C the address byte must be acknowledged just like any other byte. Or must it?

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  • \$\begingroup\$ A less contentious way to phrase this question would be just to ask about the required acknowledgement of the address byte up front. This may get clearer answers. \$\endgroup\$ – caveman Feb 8 '15 at 16:51
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I2C does not support hot swapping so devices should not be removed. And busy devices will not acknowledge.

SMBUS does not lie, it embellished a bit, but it's not a lie. It has specs designed to improve upon actual or perceived faults in I2C.

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  • \$\begingroup\$ It doesn't even appear to be an embellishment. If a device is not required to ack its address when busy, the statement is factual. \$\endgroup\$ – caveman Feb 8 '15 at 16:53

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