WHITE BROWN DA 918 Instrukcja Użytkownika Pobierz pdf (Strona 63)

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Chapter 4 Digital Input/Output and PFI

Change detection acquisitions can be buffered or nonbuffered:

• Nonbuffered Change Detection Acquisition—In a nonbuffered acquisition, data is

transferred from the cDAQ chassis directly to a PC buffer.

• Buffered Change Detection Acquisition—A buffer is a temporary storage in computer

memory for acquired samples. In a buffered acquisition, data is stored in the cDAQ chassis

onboard FIFO then transferred to a PC buffer. Buffered acquisitions typically allow for

much faster transfer rates than nonbuffered acquisitions because data accumulates and is

transferred in blocks, rather than one sample at a time.

Digital Output

To generate digital output, insert a digital output C Series I/O module in any slot on the cDAQ

chassis. The generation specifications, such as the number of channels, channel configuration,

update rate, and output range, are determined by the type of C Series I/O module used. For more

information, refer to the documentation included with your C Series I/O module(s).

With parallel digital output modules (formerly known as hardware-timed modules), you can do

multiple software-timed tasks on a single module, as well as mix hardware-timed and

software-timed digital output tasks on a single module. On serial digital output modules,

(formerly known as static digital output modules), you cannot mix hardware-timed and

software-timed tasks, but you can run multiple software-timed tasks.

You may have a hardware-timed task or a software-timed task include channels from multiple

modules, but a hardware-timed task may not include a mix of channels from both parallel and

serial modules.

Digital Output Data Generation Methods

When performing a digital output operation, you either can perform software-timed or

hardware-timed generations. Hardware-timed generations must be buffered.

Software-Timed Generations

With a software-timed generation, software controls the rate at which data is generated. Software

sends a separate command to the hardware to initiate each digital generation. In NI-DAQmx,

software-timed generations are referred to as on-demand timing. Software-timed generations are

also referred to as immediate or static operations. They are typically used for writing out a single

value.

For software-timed generations, if any DO channel on a serial digital module is used in a

hardware-timed task, no channels on that module can be used in a software-timed task.

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 chassis or provided externally.

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WHITE BROWN DA 918 Instrukcja Użytkownika Strona 63