FLEX 6000 Programmable Logic Device Family Data Sheet
Figure 6. Cascade Chain Operation
AND Cascade Chain
OR Cascade Chain
LE 2
LE 2
LE 3
d[3..0]
d[7..4]
d[3..0]
LUT
LUT
LUT
LUT
LE 3
d[7..4]
LEn + 1
LE n + 1
d[(4n-1)..4(n-1)]
LUT
d[(4n-1)..4(n-1)]
LUT
LE Operating Modes
The FLEX 6000 LE can operate in one of the following three modes:
■
■
■
Normal mode
Arithmetic mode
Counter mode
Each of these modes uses LE resources differently. In each mode, seven
available inputs to the LE—the four data inputs from the LAB local
interconnect, the feedback from the programmable register, and the
carry-in and cascade-in from the previous LE—are directed to different
destinations to implement the desired logic function. LAB-wide signals
provide clock, asynchronous clear, synchronous clear, and synchronous
load control for the register. The Altera software, in conjunction with
parameterized functions such as LPM and DesignWare functions,
automatically chooses the appropriate mode for common functions such
as counters, adders, and multipliers. If required, the designer can also
create special-purpose functions to use an LE operating mode for optimal
performance.
Figure 7 shows the LE operating modes.
Altera Corporation
13
ALTERA [ ALTERA CORPORATION ]
