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 an LUT
Configure the truth table inputs (LUTn-TRUTHSEL[2:0]) 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.
LUT Output for CCL.TRUTHn =
0x42
If CCL.TRUTHn is configured to 0x42,
the LUT output will be 1 when the inputs are ‘b001 or
‘b110 and 0 for any other combination of
inputs.