Cyclone FPGA Family Data Sheet
Preliminary Information
Figure 8. Carry Select Chain
LAB Carry-In
0
1
LAB Carry-In
Carry-In0
Sum1
Sum2
Sum3
Sum4
Sum5
A1
B1
LE1
LE2
LE3
LE4
LE5
Carry-In1
A2
B2
LUT
LUT
data1
data2
Sum
A3
B3
A4
B4
LUT
LUT
A5
B5
0
1
Carry-Out0
Carry-Out1
Sum6
Sum7
Sum8
Sum9
Sum10
A6
B6
LE6
LE7
LE8
LE9
A7
B7
A8
B8
A9
B9
A10
B10
LE10
LAB Carry-Out
The Quartus II Compiler automatically creates carry chain logic during
design processing, or the designer can create it manually during design
entry. Parameterized functions such as LPM functions automatically take
advantage of carry chains for the appropriate functions.
The Quartus II Compiler creates carry chains longer than 10 LEs by
linking LABs together automatically. For enhanced fitting, a long carry
chain runs vertically allowing fast horizontal connections to M4K
memory blocks. A carry chain can continue as far as a full column.
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Altera Corporation
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