EP3SL150F780I3N Altera, EP3SL150F780I3N Datasheet - Page 134

• Manufacturer Part Number: EP3SL150F780I3N
• Description: Stratix III
• Manufacturer: Altera

Operational Mode Descriptions
5–34
Stratix III Device Handbook, Volume 1
A single DSP block can implement up to two independent 44-bit
accumulators.
The dynamic accum_sload control signal is used to clear the
accumulation. A logic 1 value on the accum_sload signal
synchronously loads the accumulator with the multiplier result only,
while a logic 0 enables accumulation by adding or subtracting the
output of the DSP block (accumulator feedback) to the output of the
multiplier and first-stage adder.
1
This mode supports the round and saturation logic unit as it is configured
as an 18-bit multiplier accumulator. You can use the pipeline registers
and output registers within the DSP block to increase the performance of
the DSP block.
Shift Modes
Stratix III devices support the following shift modes for 32-bit input only:
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■
■
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1
The shift mode in a Stratix III device can be easily used by the soft
embedded processor such as Nios
rotate operation.
The shift mode makes use of the available multipliers to logically or
arithmetically shift left, right, or rotate the desired 32-bit data. The DSP
block is configured like the independent 36-bit multiplier mode to
perform the shift mode operations.
The arithmetic shift right requires signed input vector. During arithmetic
shift right, the sign is extended to fill the MSB of the 32-bit vector. The
logical shift right uses unsigned input vector. During logical shift right,
zeros are padded in the most significant bits shifting the 32-bit vector to
the right. The barrel shifter uses unsigned input vector and implements a
rotation function on a 32-bit word length.
Arithmetic shift left, ASL[N]
Arithmetic shift right, ASR[32-N]
Logical shift left, LSL[N]
Logical shift right, LSR[32-N]
32-bit rotator or Barrel shifter, ROT[N]
The control signal for the accumulator and subtractor is static
and therefore has to be configured at compile time.
You can switch the shift mode between these modes using the
dynamic rotate and shift control signals.
Figure 5–19
shows the shift mode configuration.
®
II to perform the dynamic shift and
Altera Corporation
October 2007