EP2S90F1020C5 Datasheet, PDF (530/768 Pages) Altera Corporation – Stratix II Device Handbook, Volume 1

Architecture
mult_is_saturated or accum_is_saturated overflow signal. At
all other times, this overflow signal is 0 when saturation is enabled or
reflects the value of the LSB of the multiplier or accumulator output.
When the design performs rounding, it adds 0x00008000 in 1.31 format to
the multiplier output, and it only uses bits [34..15] of the overall 36-bit
multiplier output. Adding 0x00008000 in 1.31 format to the 36-bit
multiplier result is equivalent to adding 0x0 0004 0000 in 2.34 format. The
16 LSBs are set to 0. Figure 6–6 shows which bits are used when the design
performs rounding and saturation for the multiplication.
6–14
Stratix II Device Handbook, Volume 2
Altera Corporation
January 2008