Measurement Computing USB-231-OEM, Руководство пользователя, Страница: 14 / 26

USB-231-OEM User's Guide Functional Details
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Figure 6. USB-231-OEM analog output connection diagram
Power-on state
The AO circuitry exhibits a short glitch when the device is powered on and when the DAQ device exits suspend
mode. After power-up, the AO circuitry is reset to 0 V.
AO range
The AO range is ± 10 V.
Minimizing glitches on the output signal
When using a DAC to generate a waveform, you may observe glitches on the output signal. These glitches are
normal; when a DAC switches from one voltage to another, it produces glitches due to released charges. The
largest glitches occur when the most significant bit of the DAC code changes. You can build a low-pass
deglitching filter to remove some of these glitches, depending on the frequency and nature of the output signal.
Generating analog output data
The USB-231-OEM can generate analog output data in two different modes – software paced and hardware
paced.
 Software paced
– Software controls the rate at which data is generated. Software sends a separate
command to the hardware to initiate each DAQ conversion. Software-paced generations are also referred to
as immediate or static operations. They are typically used for writing a single value out, such as a constant
DC voltage.
 Hardware paced
– A digital hardware signal controls the generation rate. This signal is generated
internally on your device. Hardware-paced generations have advantages over software-timed acquisitions,
such as the time between samples can be much shorter, and the timing between samples can be
deterministic (data is sampled at regular intervals).
Hardware-timed operations are buffered. During hardware-paced AO generation, data is moved from a PC
buffer to the onboard FIFO on the DAQ device using USB signal streams before it is written to the DACs one
sample at a time. Buffered generations allow for fast transfer rates because data is moved in large blocks rather
than one point at a time.
The sample mode can be either finite or continuous in a buffered I/O operation:

In finite sample mode, a specified number of samples are generated, and then the generation stops.

In continuous mode, an unspecified number of samples are generated until you stop the generation.