EP4CE40 datasheet(31/488 Pages) ALTERA

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Chapter 2: Logic Elements and Logic Array Blocks in Cyclone IV Devices

2–3

LE Operating Modes

November 2009

Altera Corporation

Cyclone IV Device Handbook,

Volume 1

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

data1

Four-Input

LUT

data2

data3

cin (from cout

of previous LE)

data4

clock (LAB Wide)

ena (LAB Wide)

aclr (LAB Wide)

CLRN

ENA

sclear

(LAB Wide)

sload

(LAB Wide)

Connection

Chain Output

Row, Column, and

Direct Link Routing

Row, Column, and

Direct Link Routing

Local Routing

Packed Register Input

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