Roland UM-3EX Owner's Manual page 46

Don't make connections like the following.
UM-3EX set to SLAVE and connected to a computer
fig.ng-double-e.eps_70
Set this to
SLAVE.
UM-3EX set to MASTER and connected to a UM-3EX connector
fig.ng-double2-e.eps_70
46
Set this to
MASTER.
First unit
Set this to
MASTER.
Set this to
SLAVE.