HP 34401A User Manual page 75

Chapter 3 Features and Functions
Triggering
External Triggering In the external trigger mode, the multimeter
will accept a hardware trigger applied to the Ext Trig terminal.
The multimeter takes one reading, or the specified number of readings
(sample count), each time Ext Trig receives a low-true pulse.
See also "External Trigger Terminal," on page 83.
The multimeter buffers one external trigger. This means that if the
multimeter is taking a reading and another external trigger occurs,
that trigger is accepted (a "Trigger ignored" error is not reported).
After the reading in progress is complete, the stored trigger satisfies
the trigger source and then the trigger is issued.
Front-Panel Operation: The external trigger mode is like the single
trigger mode except that you apply the trigger to the Ext Trig
terminal. Pressing
Single
enables the external trigger mode. The Trig annunciator turns on
when the multimeter is waiting for an external trigger.
The front-panel
Single
Remote Interface Operation:
TRIGger:SOURce EXTernal
74
to enable the single trigger mode also
key is disabled when in remote.