EP2S15 datasheet(52/238 Pages) ALTERA

52 / 238 page

2–44

Altera Corporation

Stratix II Device Handbook, Volume 1

May 2007

Digital Signal Processing Block

Modes of Operation

The adder, subtractor, and accumulate functions of a DSP block have four

modes of operation:

■

Simple multiplier

■

Multiply-accumulator

■

Two-multipliers adder

■

Four-multipliers adder

Table 2–6 shows the different number of multipliers possible in each DSP

block mode according to size. These modes allow the DSP blocks to

implement numerous applications for DSP including FFTs, complex FIR,

FIR, and 2D FIR filters, equalizers, IIR, correlators, matrix multiplication

and many other functions. The DSP blocks also support mixed modes

and mixed multiplier sizes in the same block. For example, half of one

DSP block can implement one 18 × 18-bit multiplier in multiply-

accumulator mode, while the other half of the DSP block implements four

9 × 9-bit multipliers in simple multiplier mode.

DSP Block Interface

Stratix II device DSP block input registers can generate a shift register that

can cascade down in the same DSP block column. Dedicated connections

between DSP blocks provide fast connections between the shift register

inputs to cascade the shift register chains. You can cascade registers

within multiple DSP blocks for 9 × 9- or 18 × 18-bit FIR filters larger than

four taps, with additional adder stages implemented in ALMs. If the DSP

block is configured as 36 × 36 bits, the adder, subtractor, or accumulator

stages are implemented in ALMs. Each DSP block can route the shift

Table 2–6. Multiplier Size & Configurations per DSP Block

DSP Block Mode

9 × 9

18 × 18

36 × 36

Multiplier

Eight multipliers with

eight product outputs

Four multipliers with four

product outputs

One multiplier with one

product output

Multiply-accumulator

Two 52-bit multiply-

accumulate blocks

Two-multipliers adder

Four two-multiplier adder

(two 9 × 9 complex

multiply)

Two two-multiplier adder

(one 18 × 18 complex

multiply)

Four-multipliers adder

Two four-multiplier adder

One four-multiplier adder

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