EPF8452ATC100-4N Datasheet, PDF (9/62 Pages) Altera Corporation – Programmable Logic Device Family

Altera Corporation
FLEX 8000 Programmable Logic Device Family Data Sheet
Figure 4. FLEX 8000 Carry Chain Operation
Carry-In
a1
LU
Register
s1
b1
Carry
LE1
a2
LUT
Register
s2
b2
Carry Chain
LE2
3
an
LUT
Register
sn
bn
Carry Chain
LEn
LUT
Register
Carry-Out
Carry Chain
LEn + 1
Cascade Chain
With the cascade chain, the FLEX 8000 architecture can implement
functions that have a very wide fan-in. Adjacent LUTs can be used to
compute portions of the function in parallel; the cascade chain serially
connects the intermediate values. The cascade chain can use a logical AND
or logical OR (via De Morgan’s inversion) to connect the outputs of
adjacent LEs. Each additional LE provides four more inputs to the
effective width of a function, with a delay as low as 0.6 ns per LE.
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