Specifications

The Operating
Sequence
The VT1419A has four major operating phases. Figure 3-8 shows these phases. A
trigger event starts the sequence:
1. (INPUT): the state of all digital inputs are captured and each analog input
channel that is linked to an algorithm variable is scanned.
2. (UPDATE): The update phase is a window of time made large enough to
process all variables and algorithm changes made after INIT. Its width is
specified by ALG:UPDATE:WINDOW. This window is the only time
variables and algorithms can be changed. Variable and algorithm changes
can actually be accepted during other phases, but the changes don’t take
place until an ALG:UPDATE command is received and the update phase
begins. If no ALG:UPDATE command is pending, the update phase is
simply used to accept variable and algorithm changes from the application
program (using ALG:SCAL, ALG:ARR, ALG:DEF). Data acquired by
external specialized measurement instruments can be sent to an algorithm at
this time.
3. (EXECUTE ALGS): all INPUT and UPDATE values have been made
available to the algorithm variables and each enabled algorithm is executed.
The results to be output from algorithms are stored in the Output Channel
Buffer.
4. (OUTPUT): each Output Channel Buffer value stored during (EXECUTE
ALGS) is sent to its assigned SCP channel. The start of the OUTPUT phase
relative to the Scan Trigger can be set with the SCPI command
ALG:OUTP:DELay.
Retrieving Algorithm Data
The most efficient means of acquiring data from the VT1419A is to have its
algorithms store real-number results in the FIFO or CVT. The algorithms use the
writefifo(), writecvt() and writeboth() intrinsic functions to perform this operation
as seen in Figure 3-9.
Programming the VT1419A Multifunction
Plus
Retrieving Algorithm Data
Chapter 3 81
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