ep1sgx25d Altera Corporation, ep1sgx25d Datasheet - Page 124

• Manufacturer Part Number: ep1sgx25d
• Description: Stratix Gx Device Family Data Sheet
• Manufacturer: Altera Corporation

Digital Signal Processing Block
4–58
Stratix GX Device Handbook, Volume 1
Adder/Subtractor/Accumulator
The adder/subtractor/accumulator is the first level of the adder/output
block and can be used as an accumulator or as an adder/subtractor.
Adder/Subtractor
Each adder/subtractor/accumulator block can perform addition or
subtraction using the addnsub independent control signal for each first-
level adder in 18
available in a DSP block for any configuration. For 9
addnsub[1..0] signal controls the top two one-level adders and
another addnsub[1..0] signal controls the bottom two one-level
adders. A high addnsub signal indicates addition, and a low signal
indicates subtraction. The addnsub control signal can be unregistered or
registered once or twice when feeding the adder blocks to match data
path pipelines.
The signa and signb signals serve the same function as the multiplier
block signa and signb signals. The only difference is that these signals
can be registered up to two times. These signals are tied to the same
signa and signb signals from the multiplier and must be connected to
the same clocks and control signals.
Accumulator
When configured for accumulation, the adder/output block output feeds
back to the accumulator as shown in
accum_sload[1..0] signal synchronously loads the multiplier result
to the accumulator output. This signal can be unregistered or registered
once or twice. Additionally, the overflow signal indicates the
accumulator has overflowed or underflowed in accumulation mode. This
signal is always registered and must be externally latched in LEs if the
design requires a latched overflow signal.
Summation
The output of the adder/subtractor/accumulator block feeds to an
optional summation block. This block sums the outputs of the DSP block
multipliers. In 9
the sums of two sets of four 9
is one summation providing the sum of one set of four 18
multipliers.
×
×
9-bit mode, there are two summation blocks providing
18-bit mode. There are two addnsub[1..0] signals
×
9-bit multipliers. In 18
Figure
4–33. The
×
×
18-bit mode, there
9-bit mode, one
Altera Corporation
×
February 2005
18-bit