130 Programming the VT1422A for Data Acquisition and Control Chapter 4
NOTES 1. When TRIGger:SOURce is not TIMer, ARM:SOURce must be set to
IMMediate (the *RST condition). If not, the INIT command will
generate an error -221,"Settings conflict."
2. When TRIGger:SOURce is TIMer, the trigger timer interval
(TRIG:TIM <interval>) must allow enough time to scan all channels,
execute all algorithms and update all outputs or a +3012, "Trigger
Too Fast" error will be generated during the trigger cycle. See the
TRIG:TIM command on page 397 for details.
To set the trigger source to the internal Trigger Timer (the default):
TRIG:SOUR TIMER now select ARM:SOUR
To set the trigger source to the External Trigger input connection:
TRIG:SOUR EXT an external trigger signal
To set the trigger source to a VXIbus TTLTRG line:
TRIG:SOUR TTLTRG1 the TTLTRG1 trigger line

Selecting Trigger Timer

Arm Source

Figure 4-6 shows that when the TRIG:SOUR is TIMer, the other trigger
sources become Arm sources that control when the timer will start.
The command to select the arm source is ARM:SOURce <source>.
•The <source> parameter choices are explained in the following table.
NOTE When TRIGger:SOURce is not TIMer, ARM:SOURce must be set to
IMMediate (the *RST condition). If not, the INIT command will generate
an error -221,"Settings conflict."
To set the external trigger signal as the arm source:
ARM:SOUR EXT trigger input on
connector module
Parameter Value Source of Arm (after INITiate:… command)
BUS ARM[:IMMediate]
EXTernal "TRG" signal input on terminal module
HOLD ARM[:IMMediate]
IMMediate The arm signal is always true (scan starts when an
INITiate:… command is received).
SCP SCP Trigger Bus (future SCP Breadboard)
TTLTrg<n> The VXIbus TTLTRG lines (n=0 through 7)