Logic Elements
LE Operating Modes
The MAX II LE can operate in one of the following modes:
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■
“Normal Mode”
“Dynamic Arithmetic Mode”
Each mode uses LE resources differently. In each mode, eight available
inputs to the LE, the four data inputs from the LAB local interconnect,
carry-in0and carry-in1from the previous LE, the LAB carry-in
from the previous carry-chain LAB, and the register chain connection are
directed to different destinations to implement the desired logic function.
LAB-wide signals provide clock, asynchronous clear, asynchronous
preset/load, synchronous clear, synchronous load, and clock enable
control for the register. These LAB-wide signals are available in all LE
modes. The addnsubcontrol signal is allowed in arithmetic mode.
The Quartus II software, in conjunction with parameterized functions
such as library of parameterized modules (LPM) functions, automatically
chooses the appropriate mode for common functions such as counters,
adders, subtractors, and arithmetic functions.
Normal Mode
The normal mode is suitable for general logic applications and
combinational functions. In normal mode, four data inputs from the LAB
local interconnect are inputs to a four-input LUT (see Figure 2–7). The
Quartus II Compiler automatically selects the carry-in or the data3
signal as one of the inputs to the LUT. Each LE can use LUT chain
connections to drive its combinational output directly to the next LE in
the LAB. Asynchronous load data for the register comes from the data3
input of the LE. LEs in normal mode support packed registers.
2–10Core Version a.b.c variable
MAX II Device Handbook, Volume 1
Altera Corporation
March 2008
ALTERA [ ALTERA CORPORATION ]
