The truth table in each LUT unit can generate a combinational logic output as a function of up to three inputs (LUTn-TRUTHSEL[2:0]). It is possible to realize any 3-input boolean logic function using one LUT.

Figure 1. Truth Table Output Value Selection
of a LUT

The truth table inputs (LUTn-TRUTHSEL[2:0]) are configured by writing the Input Source
Selection bit fields in the LUT Control registers:

- INSEL0 in CCL.LUTnCTRLB
- INSEL1 in CCL.LUTnCTRLB
- INSEL2 in CCL.LUTnCTRLC

Each combination of the input bits (LUTn-TRUTHSEL[2:0]) corresponds to one bit in the CCL.TRUTHn register, as shown in the table below:

LUTn-TRUTHSEL[2] | LUTn-TRUTHSEL[1] | LUTn-TRUTHSEL[0] | OUT |
---|---|---|---|

`0` |
`0` |
`0` |
TRUTHn[0] |

`0` |
`0` |
`1` |
TRUTHn[1] |

`0` |
`1` |
`0` |
TRUTHn[2] |

`0` |
`1` |
`1` |
TRUTHn[3] |

`1` |
`0` |
`0` |
TRUTHn[4] |

`1` |
`0` |
`1` |
TRUTHn[5] |

`1` |
`1` |
`0` |
TRUTHn[6] |

`1` |
`1` |
`1` |
TRUTHn[7] |

Important: Consider the unused
inputs turned off (tied low) when logic functions are created.

`0x42`

, the LUT output will be
`1`

when the inputs are `'b001`

or `'b110`

and `0`

for any other combination of inputs.