Turnigy TGY-i6 AFHDS Transmitter and 6CH Receiver

What are the differente between
Turnigy TGY-i6 AFHDS Transmitter and 6CH Receiver (Mode 1)
and
Turnigy TGY-i6 AFHDS Transmitter and 6CH Receiver (Mode 2)

Wich receivers I need for this Transmitter because I need three in totaal