VXI VT1422A, Руководство пользователя

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192 Creating and Running Algorithms Chapter 6
Reading CVT elements
An application program reads one or more CVT elements by executing the
SCPI command
[SENSe:]DATA:CVT? (@<element_list>) , where
< element_list > specifies one or more individual elements and/or a range of
contiguous elements. The following example command will help to explain
the <
element_list > syntax.
DATA:CVT? (@10,20,30:33,40:43,330)
Return elements 10, 20, 30-33,
40-43, and element 330.
Individual element numbers are isolated by commas. A contiguous range of
elements is specified by: <starting element>colon<ending element>.
Writing values to the FIFO
The FIFO, as the name implies, is a First-In-First-Out buffer. It can buffer
up to 65,024 values. This capability allows an algorithm to send a
continuous stream of data values related in time by their position in the
buffer. This can be thought of as an electronic strip-chart recorder. Each
value is sent to the FIFO by executing the Algorithm Language intrinsic
statement
writefifo(<expression>) . The following in an example algorithm
statement:
writefifo(O124); /* send output channel 24's value to the FIFO */
Since the actual algorithm execution rate can be determined (see
“Programming the Trigger Timer” on page 131), the time relationship of
readings in the FIFO is very deterministic.
Reading values from the FIFO
For a discussion on reading values from the FIFO, see “Reading Running
Algorithm Values” on page 134.
Writing values to the FIFO and CVT
The writeboth(<expression>,<cvt_element>) statement sends the value of
< expression > both to the FIFO and to a < cvt_element >. Reading these
values is done the same way as mentioned for writefifo() and writecvt() .
Setting a VXIbus
Interrupt
The algorithm language provides the function interrupt() to force a VXIbus
interrupt. This interrupt() function can be used to set bit 11 of the
STATus:OPERation register from within an algorithm. This bit could then
be enabled to generate an SRQ to the controller (see
“STATus:OPERation:ENABle” on page 382 and “*SRE” on page 404).
The following example algorithm code tests an input channel value and sets
an interrupt if it is higher or lower than set limits.
static float upper_limit = 1.2, lower_limit = 0.2;
if( I124 > upper_limit || I124 < lower_limit ) interrupt();