Data Rate Multiplier

NI Digital Waveform Generator/Analyzer Help

Edition Date: June 2013

Part Number: 370520P-01

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The NI 6544/6545 can be configured for single data rate (SDR) operation only. The NI 6547/6548 can be configured for single data rate (SDR) or double data rate (DDR) operation by setting the data rate multiplier for your acquisition and/or generation session in NI-HSDIO. The data rate multiplier can be independently configured for the generation and acquisition sessions.

Single Data Rate (SDR)

When the data rate multiplier is configured for SDR operation, generation and acquisition sessions can run on all 32 channels of the NI 6544/6545 and NI 6547/6548. In this mode, one sample is generated or acquired per clock cycle. Direction control is software-specified.

Double Data Rate (DDR)

When the data rate multiplier is configured for DDR operation, the digital waveform generator/analyzer trades channel count for data rate by generating or acquiring on half the channels but at twice the rate. This faster rate is achieved by generating data on both the rising and falling edge of the Sample clock. The NI 6547/6548 allows the user to generate or acquire data on either the lower sixteen channels (DIO <0..15>) or the upper channels (DIO <16..31>). The NI 6547/6548 also allows both acquisition and generation on the same channels at the same time. Refer to the specifications document for your device for the maximum DDR rate.

DDR mode has some important implications for some NI 6547/6548 functionality.

  • Memory UsageMemory size in samples is effectively doubled since the data width and channel count are halved.
  • Marker PositionsMarker positions have a quantization twice that of SDR mode. Refer to the specifications document for your device for more information about quantization.
  • Waveform Sizes—The size of the waveforms you save to the onboard memory have a quantization twice that of SDR mode. Refer to the specifications document for your device for more information about quantization.
  • Initial/Idle States—If a channel Idle state is configured for "hold last value," the last value held is the last DDR data sample.
  • Data WidthData width is a function of your data rate multiplier. Data width refers to how large your sample is in bytes, so using DDR mode effectively halves your allowable data width. For NI 6547/6548 devices, SDR operation has a data width of 4 bytes per sample while DDR mode has a data width of 2 bytes per sample.

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