EP2AGX95EF29C6N Datasheet, PDF (89/380 Pages) Altera Corporation – Device Interfaces and Integration

Chapter 4: DSP Blocks in Arria II Devices
DSP Block Resource Descriptions
4–13
1 You can use the rounding and saturation logic units together or independently.
Second Adder and Output Registers
The second adder register and output register banks are two banks of 44-bit registers
that you can combine to form larger 72-bit banks to support 36 × 36 output results.
The outputs of the different stages in the Arria II 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
come from the outputs of the multiplier block, first-stage adder, pipeline registers,
second-stage adder, or the rounding and saturation logic unit. Based on the DSP block
operational mode you specify, the output selection unit is automatically set by the
software, and has the option to either drive or bypass the output registers. The
exception is when the block is used in shift mode, where you dynamically control the
output-select multiplexer directly.
When the DSP block is configured in chained cascaded output mode, both of the
second-stage adders are used. The first adder is for performing a four-multiplier
adder and the second is for the chainout adder. The outputs of the four-multiplier
adder are routed to the second-stage adder registers before enters the chainout adder.
The output of the chainout adder goes to the regular output register bank. Depending
on the configuration, you can route the chainout results to the input of the next half
block’s chainout adder input or to the general fabric (functioning as regular output
registers).
You can only connect the chainin port to the chainout port of the previous DSP block
and must not be connected to general routings.
The second-stage and output registers are triggered by the positive edge of the clock
signal and are cleared on power up. The clock[3..0], ena[3..0], and aclr[3..0]
DSP block signals control the output registers in the DSP block.
December 2010 Altera Corporation
Arria II Device Handbook Volume 1: Device Interfaces and Integration