ECE 375: Digital Design II
Class 17Making 3 I/P LUT with 2, 2 I/P LUTs
Example 3:
- F = X1X2 + X3
- F1 = X1X2
- F2 = F1 + X3
F1 LUT |
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0 |
0 |
0 |
1 |
F2 LUT |
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0 |
1 |
1 |
1 |
Note: Using 2 LUTs as a 3 I/P LUT could be a good idea if the X3 signal is slower or more timing sensitive.
Example 4:
- F = (X1 + X2)X3 + X1'X2'X3' (Using 2 I/P LUTS)
- F = X1X3 + X2X3 + X1'X2'X3'
- F1 = X1X3
- F2 = X2X3
- F3 = X1'X2'
- F4 = F3X3'
- F5 = F1 + F2
- F6 = F5 + F4
This is one way of creating the logic but requires a lot of resources
F = (X1 + X2)X3 + X1'X2'X3' F1 = X1 + X2 F2 = F1X3 + F1'X3' = F1 â X3
But how many LUTs are needed? 2, one for F1, one for F2
F1 LUT (X1,X2) |
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0 |
1 |
1 |
1 |
F2 LUT (F1,X3) |
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1 |
0 |
0 |
1 |