Canon EOS 80D - Manual (Page 250)

Wireless Flash PhotographyN
250
Multiple Speedlite slave units can be fired as one flash unit or separated
into slave groups for shooting with flash ratio control.
The basic settings are shown below. By changing the [Firing group]
setting, you can shoot with various wireless flash setups with multiple
Speedlites.
Basic settings:
Flash mode : E-TTL II
Wireless func. :0
Channel
: (Same as slave units)
 [1All] Firing multiple slave Speedlites as one flash unit
Effective when you need a large flash
output. All the slave units will fire at the
same output and be controlled to obtain
a standard exposure.
No matter which firing group (A, B, or C)
the slave units belong to, they will all fire
as one group.
1
Set [Firing group] to [1All].
2
Take the picture.
Fully Automatic Shooting with Multiple External Speedlites