EP3C40 datasheet(29/274 Pages) ALTERA

29 / 274 page

Chapter 2: Logic Elements and Logic Array Blocks in the Cyclone III Device Family

2–3

LE Operating Modes

December 2011

Altera Corporation

Cyclone III Device Handbook

Volume 1

In addition to the three general routing outputs, LEs in a 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 III device family LEs operate in the following modes:

■

Normal mode

■

Arithmetic mode

LE operating modes use LE resources differently. In each mode, there are six available

inputs to the LE. These inputs include the four data inputs from the LAB local

interconnect, the LE carry-in from the previous LE carry-chain, and the register chain

connection. Each input is directed to different destinations to implement the desired

logic function. LAB-wide signals provide clock, asynchronous clear, synchronous

clear, synchronous load, and clock enable control for the register. These LAB-wide

signals are available in all LE modes.

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 III Device Family 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

EP3C40 Datasheet(PDF) 29 Page - Altera Corporation

EP3C40 Datasheet(HTML) 29 Page - Altera Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL