User`s guide

Examples
The following command selects the external trigger source. In this
configuration, the instrument is triggered once each time a low-true TTL
pulse is received on the rear-panel Ext Trig Input connector.
TRIG:SOUR EXT
INIT
The following command selects the bus (software) trigger source. Note that
the *TRG command will not be accepted unless the instrument is in the
"wait-for-trigger" state.
TRIG:SOUR BUS
INIT
*TRG
The following query returns the trigger source currently selected.
TRIG:SOUR?
Typical Response: EXT