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Operating and Programming 3
L4400 User’s Guide 75
Note: To stop a scan, send the ABORt command.
Externally Triggering a Scan
In this configuration, the instrument sweeps through the scan list once each
time a low- going TTL pulse is received on the rear-panel Ext Trig Input line
(pin 6).
• You can specify a scan count which sets the number of external pulses the
instrument will accept before terminating the scan. See “Trigger Count”
for more information.
• If the instrument receives an external trigger before it is ready to accept
one, it will buffer one trigger and then ignore any additional triggers
received (no error is generated).
• All readings from the scan are stored in volatile memory.
Readings accumulate in memory until the scan is terminated
(until the scan count is reached or until you abort the scan).
• Mx+B scaling and alarm limits are applied to measurements during the
scan and all data is stored in volatile memory.
The following program segment configures the instrument for an external
scan.
Note: To stop a scan, send the
ABORt command.
Trigger Count
Usage:
• L4421A 40- Channel Armature Multiplexer
• L4450A 64- Bit Digital I/O (digital input, counter channels only)
• L4452A Multifunction Module (digital input, totalizer channels only)
You can specify the number of triggers that will be accepted by an instrument
before returning to the “idle” state. The trigger count applies to both
scanning and non-scanning applications.
• Select a trigger count between 1 and 500,000 triggers, or continuous.
TRIG:SOURCE EXT
TRIG:COUNT 2
INIT
Select external mode
Sweep the scan list 2 times
Initiate the scan