I'm learning I2S right now and I am curious about working in an environment where 8 or so audio devices could be in the setup. 

I understand TDM mode would allow the Controller (Master in legacy terms) to read N channels on the single bit serial data line (as shown in the picture). However, I don't understand how the audio device knows when to drive the serial data line with its data. How is contention avoided? 

[![From https://d3uzseaevmutz1.cloudfront.net/pubs/appNote/AN301REV1.pdf ][1]][1]


  [1]: https://i.sstatic.net/woKX5.png