
Altera Corporation
6–21
January 2008
Stratix II Device Handbook, Volume 2
DSP Blocks in Stratix II and Stratix II GX Devices
Operational
Modes
The DSP block can be used in one of four basic operational modes, or a
combination of two modes, depending on the application needs.
Table 6–7 shows the four basic operational modes and the number of
multipliers that can be implemented within a single DSP block
depending on the mode.
The Quartus II software includes megafunctions used to control the mode
of operation of the multipliers. After you make the appropriate parameter
settings using the megafunction’s MegaWizard Plug-In Manager, the
Quartus II software automatically configures the DSP block.
Stratix II and Stratix II GX DSP blocks can operate in different modes
simultaneously. For example, a single DSP block can be broken down to
operate a 9 × 9 multiplier as well as an 18 × 18 multiplier-adder where
both multiplier's input a and input b have the same sign representations.
This increases DSP block resource efficiency and allows you to implement
more multipliers within a Stratix II or Stratix II GX device. The Quartus II
software automatically places multipliers that can share the same DSP
block resources within the same block.
Additionally, you can set up each Stratix II or Stratix II GX DSP block to
dynamically switch between the following three modes:
■
Up to four 18-bit independent multipliers
■
Up to two 18-bit multiplier-accumulators
■
One 36-bit multiplier
Table 6–7. DSP Block Operational Modes
Mode
Number of Multipliers
9 × 9
18 × 18
36 × 36
Simple multiplier
Eight multipliers
with eight product
outputs
Four multipliers
with four product
outputs
One multiplier
Multiply
accumulate
-
Two 52-bit
multiply-
accumulate blocks
-
Two-multiplier
adder
Four two-multiplier
adder (two 9 × 9
complex multiply)
Two two-multiplier
adder (one
18 × 18 complex
multiply)
-
Four-multiplier
adder
Two four-multiplier
adder
One four-multiplier
adder
-