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Following the completion of the process, subsequent readings from the buffer will return 120-n pre-
trigger readings, followed by n post trigger readings. In the case where trigger occurred before the buffer
is filled, there will be some NULL readings in the buffer, followed by pre-trigger and post-trigger
readings. Following capture use the

DMMGetTriggerInfo

() function to retrieve information such as the

number of NULL readings, Pre-Trigger samples and buffer fill cycles.

4.14.1.2 Delayed Triggered Operation

In this trigger mode of operation, following the reception of the selected trigger edge, the DMM waits for
the specified delay, and then it takes from 1 to 120 (or 1 to 80 if high resolution) measurements. The
delay can be set from 10us to 1s.

The specified number of measurements is stored in the buffer. At the end of this operation, the internal
buffer pointer points to the beginning of the buffer, such that reading the buffer starts with the first sample
taken. To read all samples resulting from this operation, use one of the buffer read functions. See

DMMDelayedTrigger

() function for details.

4.14.1.3 Long Trigger Operation (SMU2064 with ‘R’ option installed)

In this hardware trigger mode the DMM can handle multiple trigger events. The DMMLongTrigger()
function provides the facility to receiv multiple trigger pulses, responding to each with multiple samples
taken at precise times relative to the trigger. The trigger signal source can be selected from either one of
the PXI trigger inputs or from the DIN-7 source at the panel of the SMU2064 DMM. The hardware
responds to a positive edge on the trigger input. The trigger pulse must be at least 50µs wide. The Long
Trigger function will accept one to 50,000 trigger events (Tc), responding to each trigger it takes 1 to
50,000 samples (Sc), or a total of Tc * Sc samples (1 to 2.5e9). The time from the positive edge of the
trigger signal to the first sample, and the sample to sample time interval, (Td), can be a value between
100us and 3,600s, settable in increments of 1µs. The total time required for acquisition following each
trigger event is Sc * Td. To prevent timing conflicts and data over-runs, set Td to a value greater than the
Aperture plus the time to transmit the measurements and the overhead time to process each measurement.
The latter is specified in the manual as overhead time. The DMM Sync output may be activated to
monitor and observe these relations. To prevent overrun errors it is required that readings are retrieved in
real time, as they become available. This is particularly important when running fast and long. To
improve performance use a tight reading loop and set a high Thread priority. Apperture must be set to
160ms or lower value. Read Interval must be set to zero (default).

Figure 4-13. DMMLongTrigger timing diagram.

4.14.2 Analog Threshold Trigger

This mode of operation is entered by issuing the

DMMArmAnalogTrigger()

command. In this mode,

while waiting for a trigger event, the DMM makes repeated measurements and places them in the internal
buffer, as to provide pre-trigger samples. All measurements are made using the currently set range,
function, Aperture and Read Interval. Trigger event occurs when the input value transverses through the
set Threshold (

dThresh

) value, in the currently set directions dictated by Edge (see

DMMSetTrigPolarity()

). Following the trigger point, if enabled, the Sync output is activated (see

DMMSetSync()

), and

iPostSamples

measurements are taken. At the end of this process the Sync output

is deactivated. This mode may be aborted by issuing the Disarm command

(DMMDisarmTrigger())

Use

DMMArmAnalogTrigger