Keithley 2002

One-shot triggering
Our older 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 2002 gives you:
• Explicit control over the trigger source (the
TRIGger subsystem).
• A two-level control for arming the instrument for triggers.
• A way for completely disabling triggers.
Changing any of the settings in the
TRIGger subsystem does not automatically arm the Model
2002 for triggers.
The following program sets up the Model 2002 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 in INIT, ARM;LAY1, ARM:LAY2, and TRIG subsystems
'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 2002 receives the INITiate command, it stops in the TRIGger layer of the
trigger model, waiting for a pulse on the external trigger jack. Each time a pulse arrives on the
external trigger jack, the Model 2002 takes one reading. Because
TRIGger:COUNt has been set
to
INFinity, the trigger model never exits from the TRIGger layer. You can send the ABORt com-
mand to put the trigger model in the idle state, disabling triggers until another
INITiate com-
mand is sent.
3-20 IEEE-488 Bus Operation