| XC3000 | XC4000E | XC4000X | XC5200 | XC9000 | Spartan | SpartanXL | Virtex |
|---|---|---|---|---|---|---|---|
| N/A | N/A | N/A | N/A | N/A | N/A | N/A | Primitive |
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 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.
| Inputs | Outputs | ||
|---|---|---|---|
| I2 | I1 | I0 | O |
| 0 | 0 | 0 | INIT[0] |
| 0 | 0 | 1 | INIT[1] |
| 0 | 1 | 0 | INIT[2] |
| 0 | 1 | 1 | INIT[3] |
| 1 | 0 | 0 | INIT[4] |
| 1 | 0 | 1 | INIT[5] |
| 1 | 1 | 0 | INIT[6] |
| 1 | 1 | 1 | INIT[7] |
| INIT = binary equivalent of the hexadecimal number assigned to the INIT attribute | |||
LUT3 Function Table
