VXI VT1422A - Manual (Page 133)

Programming the VT1422A for Data Acquisition and Control 131 Chapter 4
Programming the
Trigger Timer
When the VT1422A is triggered, it begins its instrument operation cycle.
The time it takes to complete a cycle is the minimum interval setting for the
Trigger Timer. If programmed to a shorter time, the module will generate a
"Trigger too fast" error. How can this minimum time be determined? After
all algorithms are defined, send the ALG:TIME? query with its <alg_name>
parameter set to ’MAIN’. This causes the VT1422A’s driver to analyze the
time required for all four phases of the operation cycle: Input, Update,
Calculate, and Output. The value returned from ALG:TIME? ’MAIN’ is the
minimum allowable Trigger Timer interval required to avoid the "Trigger
too fast" error. With this information, execute the command TRIGger:TIMer
<interval> and set <interval> to the desired time that is equal to or greater
than the minimum.
Setting the
Trigger Counter
The Trigger Counter controls how many trigger events will be allowed to
start an input-calculate-output cycle. When the number of trigger events set
with the TRIGger:COUNt command is reached, the module returns to the
Trigger Idle State (needs to be INITiated again). The default Trigger Count
is 1. Note that this default was chosen to make testing data acquisition scan
lists easier (only one scan list of data in the FIFO). For algorithm operation,
changing the count to INFinite (can be triggered an unlimited number of
times) is probably desired. This setting will be used most often for
uninterrupted execution of control algorithms.
To set the trigger count to fifty (perhaps to help debug an algorithm):
TRIG:COUNT 50
execute algorithms 50 times then
return to Trig Idle State.
Sending Trigger
Signals to
Other Instruments
The VT1422A can output trigger signals on any of the VXIbus TTLTRG
lines. Use the OUTPut:TTLTrg<n>[:STATe] ON | OFF command to select
one of the TTLTRG lines and then choose the source that will drive the
TTLTRG line with the command OUTPut:TTLTrg:SOURce command.
For details, see OUTP:TTLTRG commands starting on page 319.
To output a signal on the TTLTRG1 line each time the Trigger Timer cycles,
execute the commands:
TRIG:SOUR TIMER
select trig timer as trig source
OUTP:TTLTRG1 ON
select and enable TTLTRG1 line
OUTP:TTLTRG:SOUR TRIG
each trigger output on
TTLTRG1