LUT1, 2, 3, 4

1-, 2-, 3-, 4-Bit Look-Up-Table with General Output

LUT1, LUT2, LUT3, and LUT4 are, respectively, 1-, 2-, 3-, and 4-bit look-up-tables (LUTs) with general output (O).

A mandatory INIT attribute, with an appropriate number of hexadecimal digits for the number of inputs, must be attached to the LUT to specify its function.

LUT1 provides a look-up-table version of a buffer or inverter.

LUTs are the basic Virtex and Spartan2 building blocks. Two LUTs are available in each CLB slice; four LUTs are available in each CLB. The variants, “LUT1_D, LUT2_D, LUT3_D, LUT4_D” and “LUT1_L, LUT2_L, LUT3_L, LUT4_L,” provide additional types of outputs that can be used by different timing models for more accurate pre-layout timing estimation.

Table 7_1 LUT3 Function Table