2–2
Chapter 2: Logic Elements and Logic Array Blocks in the Cyclone III Device Family
Logic Elements
Figure 2–1 shows the LEs for the Cyclone III device family.
Figure 2–1. Cyclone III Device Family LEs
Register Chain
Routing from
previous LE
Register Bypass
LAB-Wide
Synchronous LAB-Wide
Programmable
Register
Load
Synchronous
Clear
LE Carry-In
data 1
data 2
Row, Column,
And Direct Link
Routing
Synchronous
Load and
Clear Logic
Carry
Chain
Look-Up Table
data 3
D
Q
(LUT)
data 4
ENA
CLRN
Row, Column,
And Direct Link
Routing
labclr1
labclr2
Asynchronous
Clear Logic
Chip-Wide
Reset
Local
Routing
Register Feedback
(DEV_CLRn)
Clock &
Clock Enable
Select
Register Chain
Output
labclk1
LE Carry-Out
labclk2
labclkena1
labclkena2
LE Features
You can configure the programmable register of each LE for D, T, JK, or SR flipflop
operation. Each register has data, clock, clock enable, and clear inputs. Signals that
use the global clock network, general-purpose I/O pins, or any internal logic can
drive the clock and clear control signals of the register. Either general-purpose I/O
pins or the internal logic can drive the clock enable. For combinational functions, the
LUT output bypasses the register and drives directly to the LE outputs.
Each LE has three outputs that drive the local, row, and column routing resources. The
LUT or register output independently drives these three outputs. Two LE outputs
drive the column or row and direct link routing connections, while one LE drives the
local interconnect resources. This allows the LUT to drive one output while the
register drives another output. This feature, called register packing, improves device
utilization because the device can use the register and the LUT for unrelated
functions. The LAB-wide synchronous load control signal is not available when using
register packing. For more information on the synchronous load control signal, refer
to “LAB Control Signals” on page 2–6.
The register feedback mode allows the register output to feed back into the LUT of the
same LE to ensure that the register is packed with its own fan-out LUT, providing
another mechanism for improved fitting. The LE can also drive out registered and
unregistered versions of the LUT output.
Cyclone III Device Handbook
Volume 1
December 2011 Altera Corporation
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