VXI VT1422A - Manual (Page 131)

Programming the VT1422A for Data Acquisition and Control 129 Chapter 4
Setting up the Trigger System
Arm and Trigger
Sources
Figure 4-6 shows the trigger and arm model for the VT1422A. Note that
when the Trigger Source selected is TIMer (the default), the remaining
sources become Arm Sources. Using ARM:SOUR allows an event to be
specified that must occur in order to start the Trigger Timer. The default
Arm source is IMMediate (always armed).
Selecting the
Trigger Source
In order to start an instrument operation cycle, a trigger event must occur.
The source of this event is selected with the TRIGger:SOURce <source>
command. The following table explains the possible choices for <source>.
BUS
EXTernal
HOLD
IMMediate
TTLTrg
SCP Trg
ARM
/TRIGge
r
S
our
ce
T
ri
gge
r
S
o
u
rc
e
S
el
ec
tor
A
rm
S
o
u
rc
e
S
el
ec
to
r
ARM:SOURce
TRIGger:TIMer
Trigger
Timer
TIMer
Trigger
Enable
TRIGger:SOURce
Internal
Trigger Signal
Trigger
Counter
TRIGger:COUNt
Figure 4-6. Logical Arm and Trigger Model
Parameter Value Source of Trigger (after INITiate: … command)
BUS TRIGger[:IMMediate], *TRG, GET (for GPIB)
EXTernal "TRG" signal input on terminal module
HOLD TRIGger[:IMMediate]
IMMediate The trigger signal is always true (scan starts when an
INITiate:
… command is received).
SCP SCP Trigger Bus (future SCP Breadboard)
TIMer The internal trigger interval timer (must set Arm source)
TTLTrg The VXIbus TTLTRG lines (n=0 through 7)