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•
Only one simultaneous update task can run at a time
•
A hardware-timed AO task and a simultaneous update AO task cannot run at the same
time
Hardware-Timed Generations
With a hardware-timed generation, a digital hardware signal controls the rate of the generation.
This signal can be generated internally on the controller or provided externally.
Hardware-timed generations have several advantages over software-timed acquisitions:
•
The time between samples can be much shorter
•
The timing between samples is deterministic
•
Hardware-timed acquisitions can use hardware triggering
Hardware-Timed Single Point (HWTSP) Mode
In HWTSP mode, samples are acquired or generated continuously using hardware timing and
no buffer. You must use the sample clock or change detection timing types. No other timing
types are supported.
Use HWTSP mode if you need to know if a loop executes in a given amount of time, such as
in a control application. Because there is no buffer, if you use HWTSP mode, ensure that reads
or writes execute fast enough to keep up with hardware timing. If a read or write executes late,
it returns a warning.
Note
DSA modules do not support HWTSP mode.
Buffered Analog Input
A buffer is a temporary storage in computer memory for generated samples. In a buffered
generation, data is moved from a host buffer to the cRIO controller onboard FIFO before it is
written to the C Series modules.
One property of buffered I/O operations is sample mode. The sample mode can be either finite
or continuous:
•
Finite—Finite sample mode generation refers to the generation of a specific,
predetermined number of data samples. After the specified number of samples is written
out, the generation stops.
•
Continuous—Continuous generation refers to the generation of an unspecified number of
samples. Instead of generating a set number of data samples and stopping, a continuous
generation continues until you stop the operation. There are three different continuous
generation modes that control how the data is written. These modes are regeneration,
onboard regeneration, and non-regeneration:
–
In regeneration mode, you define a buffer in host memory. The data from the buffer
is continually downloaded to the FIFO to be written out. New data can be written to
cRIO-904x User Manual | © National Instruments | 55
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