ACEX 1K Programmable Logic Device Family Data Sheet
Figure 8. ACEX 1K Logic Element
Register Bypass
Carry-In
Cascade-In
Programmable
Register
data1
data2
data3
data4
Look-Up
Table
(LUT)
To FastTrack
Interconnect
Carry
Chain
Cascade
Chain
PRN
D
Q
ENA
CLRN
To LAB Local
Interconnect
labctrl1
labctrl2
Clear/
Preset
Logic
Chip-Wide
Reset
Clock
Select
labctrl3
labctrl4
Carry-Out
Cascade-Out
The programmable flipflop in the LE can be configured for D, T, JK, or SR
operation. The clock, clear, and preset control signals on the flipflop can
be driven by global signals, general-purpose I/ O pins, or any internal
logic. For combinatorial functions, the flipflop is bypassed and the LUT’s
output drives the LE’s output.
The LE has two outputs that drive the interconnect: one drives the local
interconnect, and the other drives either the row or column FastTrack
Interconnect routing structure. The two outputs can be controlled
independently. For example, the LUT can drive one output while the
register drives the other output. This feature, called register packing, can
improve LE utilization because the register and the LUT can be used for
unrelated functions.
The ACEX 1K architecture provides two types of dedicated high-speed
data paths that connect adjacent LEs without using local interconnect
paths: carry chains and cascade chains. The carry chain supports high-
speed counters and adders, and the cascade chain implements wide-input
functions with minimum delay. Carry and cascade chains connect all LEs
in a LAB and all LABs in the same row. Intensive use of carry and cascade
chains can reduce routing flexibility. Therefore, the use of these chains
should be limited to speed-critical portions of a design.
16
Altera Corporation
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