EP4CE30F29C7N Datasheet, PDF (31/488 Pages) Altera Corporation – Cyclone IV Device Handbook, Volume 1

Chapter 2: Logic Elements and Logic Array Blocks in Cyclone IV Devices
2–3
LE Operating Modes
In addition to the three general routing outputs, LEs in an LAB have register chain
outputs, which allows registers in the same LAB to cascade together. The register
chain output allows the LUTs to be used for combinational functions and the registers
to be used for an unrelated shift register implementation. These resources speed up
connections between LABs while saving local interconnect resources.
LE Operating Modes
Cyclone IV LEs operate in the following modes:
■ Normal mode
■ Arithmetic mode
The Quartus^® II software automatically chooses the appropriate mode for common
functions, such as counters, adders, subtractors, and arithmetic functions, in
conjunction with parameterized functions such as the library of parameterized
modules (LPM) functions. You can also create special-purpose functions that specify
which LE operating mode to use for optimal performance, if required.
Normal Mode
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 (Figure 2–2). The Quartus II Compiler automatically selects the
carry-in (cin) or the data3 signal as one of the inputs to the LUT. LEs in normal mode
support packed registers and register feedback.
Figure 2–2 shows LEs in normal mode.
Figure 2–2. Cyclone IV Device LEs in Normal Mode
Register Chain
Connection sload
sclear
(LAB Wide) (LAB Wide)
Packed Register Input
data1
data2
data3
cin (from cout
of previous LE)
data4
Four-Input
LUT
clock (LAB Wide)
ena (LAB Wide)
aclr (LAB Wide)
Q
D
ENA
CLRN
Register Bypass
Register Feedback
Row, Column, and
Direct Link Routing
Row, Column, and
Direct Link Routing
Local Routing
Register
Chain Output
November 2009 Altera Corporation
Cyclone IV Device Handbook,
Volume 1