I2C Master-Slave communication

Projects Networking, Protocols, and Devices
1

Hi everybody, I have one question about master and slave.
In a setup with a master and 2 slaves, where:

Slaves' task -> Reading any RFID tag or card and sending the data (a 4 bytes ID) to the Master
Master's task -> Acquiring the data (ID) from the slaves, whenever they read any card, and reply if the card is allowed or not (of course the Master has saved in the EEPROM all the allowed ID's and can compare them)

Is there a way for the master to do nothing till data is sent by one of the slaves?

2

You could add an extra "interrupt" wire.
Or use millis() to check the Slaves for example 5 times per second.

What is "do nothing" ? Why do you want that ? If you unplug the Arduino board, and it has no power, then it is doing nothing.