Bus Mastering Dma - Omega OMB-DAQBOARD-3000 Series User Manual

Bus Mastering DMA

The DaqBoard/3000 series supports Bus Mastering DMA. Multiple DMA channels allow analog and
digital/counter input data, as well as analog and digital output data to flow between the PC and the
DaqBoard/3000 series without consuming valuable CPU time. The driver supplied with the
DaqBoard/3000, as well as all other third-party software support such as LabVIEW®, automatically
utilize Bus Mastering DMA to efficiently conduct I/O from the PC to the DaqBoard.
Triggering
Triggering can be the most critical aspect of a data acquisition application. The DaqBoard/3000 series
supports a full complement of trigger modes to accommodate any measurement situation.
Hardware Analog Triggering. TheDaqBoard/3000 Series uses true analog triggering, whereby the trigger
level programmed by the user sets an analog DAC, which is then compared in hardware to the analog input
level on the selected channel. The result is analog trigger latency which is guaranteed to be less than1 µs.
Any analog channel can be selected as the trigger channel, including built-in or PDQ30 expansion
channels. The user can program both the trigger level, as well as the rising or falling edge and hysteresis.
Digital Triggering. A separate digital trigger input line is provided, allowing TTL-level triggering with
latencies guaranteed to be less than 1 µs. Both the logic levels (1 or 0), as well as the rising or falling edge
can be programmed for the discrete digital trigger input.
Pattern Triggering. The user can specify a 16-bit digital pattern to trigger an acquisition, including the
ability to mask or ignore specific bits.
Software-Based Channel Level Triggering. This mode differs from the modes just discussed because the
readings [analog, digital, or counter] are interrogated by the PC in order to detect the trigger event.
Triggering can also be programmed to occur when one of the counters reaches, exceeds, or is within a
programmed window.
Any of the built-in counter/totalizer channels can be programmed as a trigger source. Triggers can be
detected on scanned digital input channel patterns as well. Normally software-based triggering results in
long latencies from the moment a trigger condition is detected until the instant data is acquired. However,
theDaqBoard/3000 Series circumvents this undesirable situation by use of pre-trigger data. Specifically,
when software-based-triggering is employed, and the PC detects that a trigger condition has occurred,
(which may be thousands of readings after the actual occurrence of the signal), the DaqBoard driver
automatically looks back to the location in memory, to where the actual trigger-causing measurement
occurred. The acquired data presented to the user begins at the point where the trigger-causing
measurement occurs. The maximum latency in this mode is equal to one scan period
Stop Trigger. Any of the software trigger modes previously described, including scan count, can be used
to stop an acquisition. Thus an acquisition can be programmed to begin on one event, such as a voltage
level, and then can stop on another event, such as a digital pattern.
Pre-Triggering and Post-Triggering Modes. Six modes of pre-triggering and post-triggering are
supported, providing a wide variety of options to accommodate any measurement requirement. When
using pre-trigger, the user must use software-based triggering to initiate an acquisition. The six modes are:
No pre-trigger, post-trigger stop event. This, the simplest of modes, acquires data upon receipt of
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the trigger, and stops acquiring upon receipt of the stop-trigger event.
Fixed pre-trigger with post-trigger stop event. In this mode, the user specifies the number of pre-
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trigger readings to be acquired, after which, acquisition continues until a stop-trigger event occurs.
No pre-trigger, infinite post-trigger. No pre-trigger data is acquired in this mode. Instead, data is
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acquired beginning with the trigger event, and is terminated when the operator issues a command
to halt the acquisition.
Fixed pre-trigger with infinite post-trigger. The user specifies the amount of pre-trigger data to
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acquire, after which the system continues to acquire data until the program issues a command to
halt acquisition.
DaqBoard/3000 Series User's Manual Daq Systems and Device Overviews 1-9
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