I2C Multiple Masters

Question

I am working on Ti's EK-TM4C1294XL which is basically a Arm Cortex M4 evaluation board. I was going through I2C bus of the same and have the following question regarding the I2C bus.

I understand I2C support multi master multi slave configuration. So when we want to send data from a particular master to a particular slave we write first the slave address on the bus from that master and after receiving the Ack transmits the data to that slave.

So in the same situation i want to receive data from a particular slave to a particular master but can the slave start the communication? Like suppose slave is a ADC and once the conversion is done send the converted data to a particular master. Is this possible in I2C?

Answer 1

So in the same situation i want to receive data from a particular slave to a particular master but can the slave start the communication? Like suppose slave is a ADC and once the conversion is done send the converted data to a particular master. Is this possible in I2C?

A device which is a pure I²C slave can not start an I²C transaction. This holds for both multi- and single-master I²C buses.

However, some slave devices can alert the master out of band, not through I²C. When the master sees the alert, it will initiate the transaction. For this purpose, some ADCs have discrete digital outputs which correspond to the state of the A/D conversion. (For example, the AD7998 has got an ALERT/BUSY pin and an I²C connection for readout and configuration.)

If there is a multi-master bus, then a device could switch its role on the fly from master to slave. Then it can initiate an I²C transaction as a master. It would have to be a microcontroller with its own firmware. The vast majority of hard I²C devices are bus slaves, although there are a handful of hard I²C devices that are bus masters. I've never heard of a hard I²C device that would switch from master to slave.

By the way, here's a related thread: https://electronics.stackexchange.com/a/232135 .