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Look-Up Table 1D (FPGA Module)

LabVIEW FPGA Module 8.2 Help
August 2006

NI Part Number:
371599B-01

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Provides a general-purpose block of initialized memory. Use look-up tables to store waveforms for signal generation, to model nonlinear systems, and for arithmetic computations. If you use the Look-Up Table 1D Express VI in a single-cycle Timed Loop, wire the outputs directly to uninitialized shift registers or feedback nodes. The Look-Up Table 1D Express VI takes an entire clock cycle to execute in a single-cycle Timed Loop.

Dialog Box Options
Block Diagram Inputs
Block Diagram Outputs

Dialog Box Options

ParameterDescription
Look-Up Table SpecificationsContains the following options:
  • Number of elements—Specifies the number of available elements in the look-up table.
  • Data type—Specifies the data type of the output data from the look-up table. Choose among signed and unsigned integers. If you select an unsigned integer, you cannot select the Sine Wave or Cosine Wave modes in the Configure Segment dialog box.
  • Interpolate data—Uses the fractional index (x2^16) to linearly interpolate between look-up table entries corresponding to address and address + 1. The result of the multiplication by fractional index (x2^16) is a 32-bit number. The VI truncates the lower 16 bits to return data out. If you place a checkmark in this checkbox, the Look-Up Table 1D Express VI takes at least two clock cycles to execute. Do not place a checkmark in the Interpolate data checkbox if the Look-Up Table 1D Express VI is in a single-cycle Timed Loop.
  • Memory size—Displays the amount of memory the FPGA uses for the look-up table.
  • Define Table—Opens the Define Table dialog box. You can initialize the memory block by editing points individually, defining linear segments, using predefined functions, or calling an initialization VI you create.
Function NameSpecifies a name for the look-up table to identify functionality of different instances of the Look-Up Table 1D Express VI on the block diagram.
Table PreviewDisplays a preview of the data in the look-up table.

Block Diagram Inputs

ParameterDescription
addressSpecifies an element of the look-up table. If address exceeds the Number of elements range you specify in the Configure Look-Up Table 1D dialog box, LabVIEW attempts to wrap the value into the valid range by using the lowest log2(Number of elements) bits of address.

If Number of elements is an exact power of 2, any address input results in valid data out from the look-up table. For other sizes, the resulting wrapped address still exceeds the range. The VI returns 0 for data out.

fractional index (x2^16)Specifies the 16-bit integer the VI interprets as a positive fractional number in the range 0 <= fractional index (x2^16) < 1 to compute the linearly interpolated output between adjacent look-up table elements. Multiply the fractional index you want to use by 2^16 (65536) to convert it to a U16 integer data type for use on FPGA targets. For example, if you want a fractional index of .5, enter .5 x 2^16 = 32768 for the fractional index (x 2^16) input. The VI uses this input only if you place a checkmark in the Interpolate data checkbox in the Configure Look-Up Table 1D dialog box.

Block Diagram Outputs

ParameterDescription
data outThe result of the table look-up operation. Specify the data type of this parameter in the Configure Look-Up Table 1D dialog box with the Data type selection.

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