Cyclone FPGA Family Data Sheet
Preliminary Information
Each LE’s programmable register can be configured for D, T, JK, or SR
operation. Each register has data, true asynchronous load data, clock,
clock enable, clear, and asynchronous load/preset inputs. Global signals,
general-purpose I/O pins, or any internal logic can drive the register’s
clock and clear control signals. Either general-purpose I/O pins or
internal logic can drive the clock enable, preset, asynchronous load, and
asynchronous data. The asynchronous load data input comes from the
data3input of the LE. For combinatorial 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 can drive these three outputs
independently. Two LE outputs drive column or row and direct link
routing connections and one drives 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. Another special packing mode allows the register output to
feed back into the LUT of the same LE so that the register is packed with
its own fan-out LUT. This provides another mechanism for improved
fitting. The LE can also drive out registered and unregistered versions of
the LUT output.
LUT Chain & Register Chain
In addition to the three general routing outputs, the LEs within an LAB
have LUT chain and register chain outputs. LUT chain connections allow
LUTs within the same LAB to cascade together for wide input functions.
Register chain outputs allow registers within the same LAB to cascade
together. The register chain output allows an LAB to use LUTs for a single
combinatorial function and the registers to be used for an unrelated shift
register implementation. These resources speed up connections between
LABs while saving local interconnect resources. See “MultiTrack
Interconnect” on page 17 for more information on LUT chain and register
chain connections.
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Altera Corporation
ALTERA [ ALTERA CORPORATION ]
