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. Simply
sending a command to a non-SCPI DMM to change any of the trigger controls causes the instru-
ment to arm itself for triggers.
The SCPI trigger model implemented in the Model 2000 gives you:
• 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 2000 for triggers.
The following program sets up the Model 2000 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 2000 receives the
INITiate
command, it stops at the control source in the
trigger model, waiting for a trigger pulse. Each time a pulse arrives at the Trigger Link connec-
tor, the Model 2000 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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