EP3SL150F780I3N Altera, EP3SL150F780I3N Datasheet - Page 117

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

Altera Corporation
October 2007
Round and Saturation Stage
The round and saturation logic units are located at the output of the 44-bit
second-stage adder (round logic unit followed by the saturation logic
unit). There are two round and saturation logic units per half DSP block.
The input to the round and saturation logic unit can come from one of the
following stages:
■
■
■
■
These stages are discussed in detail in
on page
The round and saturation logic unit is controlled by the dynamic round
and saturate signals, respectively. A logic 1 value on the round and/or
saturate enables the round and/or saturate logic unit, respectively.
1
Second Adder and Output Registers
The second adder register and output register banks are two banks of
44-bit registers that can also be combined to form larger 72-bit banks to
support 36 × 36 output results.
The outputs of the different stages in the Stratix III devices are routed to
the output registers through an output selection unit. Depending on the
operational mode of the DSP block, the output selection unit selects
whether the outputs of the DSP blocks comes from the outputs of the
multiplier block, first-stage adder, pipeline registers, second-stage adder,
or the round and saturation logic unit. The output selection unit is set
automatically by the software, based on the DSP block operational mode
you specified, and has the option to either drive or bypass the output
registers. The exception is when the block is used in shift mode, in which
case the user dynamically controls the output-select MUX directly.
When the DSP block is configured in “chained cascaded” output mode,
both of the second-stage adders are used. The first one is used for
performing Four-Multiplier Adder and the second is used for the
chainout adder. The outputs of the Four-Multiplier Adder are routed to
the second-stage adder registers before it enters the chainout adder. The
output of the chainout adder goes to the regular output register bank.
Output of the multiplier (independent multiply mode in 18 × 18)
Output of the first-stage adder (Two-Multiplier Adder)
Output of the pipeline registers
Output of the second-stage adder (Four-Multiplier Adder,
Multiply-Accumulate Mode in 18 × 18)
5–18.
You can use the round and saturation logic units together or
independently.
Stratix III Device Handbook, Volume 1
“Operational Mode Descriptions”
DSP Blocks in Stratix III Devices
5–17