Canon Speedlite 580EX II Instruction Manual page 32

Set the Speedlite to the camera's
Press the
c@>
button
so
the
aperture setting bllnks.
Turn the
<@>
dial to set the
aperture, then press the
<@>
button.
I
nnot connect a
Speedllta to
anether
Speedlite's
PC terminal with
c
cord.
The second SpesdlitewilI
not
fire.