One-shot triggering
Other DMMs generally have two types of triggering: one-shot and continuous. In one-shot,
each activation of the selected trigger source causes one reading. In continuous, the DMM is idle
until the trigger source is activated, at which time it begins taking readings at a specified rate.
Typical trigger sources are:
• IEEE-488 talk
• IEEE-488 Group Execute Trigger (GET)
• “X” command
• External trigger (rear panel BNC)
Arming the instrument to respond to triggers is implicit in the non-SCPI DMMs. Sending a
command to a non-SCPI DMM to change any of the trigger controls causes the instrument to
arm itself for triggers.
The SCPI trigger model implemented in the Model 2010 gives:
• Explicit control over the trigger source (the TRIGger subsystem).
• A way for completely disabling triggers.
Changing any of the settings in the TRIGger subsystem does not automatically arm the
Model 2010 for triggers.
The following program sets up the Model 2010 to take one reading each time it receives an
external trigger pulse.
'Example program to demonstrate one-shot external triggering
'For QuickBASIC 4.5 and CEC PC488 interface card
'Edit the following line to where the QuickBASIC
'libraries are on your computer
'$INCLUDE: 'c:\qb45\ieeeqb.bi'
'Initialize the CEC interface as address 21
CALL initialize(21, 0)
'Reset controls and put trigger model in IDLE state
CALL SEND(16, "*rst", status%)
CALL SEND(16, "trig:sour ext;coun inf", status%)
'start everything
CALL SEND(16, "init", status%)
After the Model 2010 receives the INITiate command, it stops at the control source in the trig-
ger model, waiting for a trigger pulse. Each time a pulse arrives at the Trigger Link connector,
the Model 2010 takes one reading. Because TRIGger:COUNt has been set to INFinity, the
instrument never enters the idle state. You can send the ABORt command to put the instrument
in the idle state, disabling triggers until another INITiate command is sent.
C-4 Example Programs
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