DK-DEV-4SGX230N Altera, DK-DEV-4SGX230N Datasheet - Page 112

• Manufacturer Part Number: DK-DEV-4SGX230N
• Description: KIT DEVELOPMENT STRATIX IV
• Manufacturer: Altera
• Series: Stratix® IVr
• Type: FPGAr

Specifications of DK-DEV-4SGX230N

• Contents: Development Board, Universal Power Supply, Cables and Software
• Silicon Manufacturer: Altera
• Core Architecture: FPGA
• Core Sub-architecture: Stratix
• Silicon Core Number: EP4S
• Silicon Family Name: Stratix IV GX
• Rohs Compliant: Yes
• For Use With/related Products: EP4SGX230K
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 544-2594

4–32
Stratix IV Device Handbook Volume 1
Rounding and Saturation Mode
1
Rounding and saturation functions are often required in DSP arithmetic. Use
rounding to limit bit growth and its side effects; use saturation to reduce overflow and
underflow side effects.
Two rounding modes are supported in Stratix IV devices:
■
■
You must select one of these two options at compile time.
Round-to-nearest-integer provides the biased rounding support and is the simplest
form of rounding commonly used in DSP arithmetic. The round-to-nearest-even
method provides unbiased rounding support and is used where DC offsets are a
concern.
Table 4–6. Example of Round-To-Nearest-Even Mode
Table 4–7
6-bit input is rounded to 4 bits. The main difference between the two rounding
options is when the residue bits are exactly halfway between its nearest two integers
and the LSB is zero (even).
Table 4–7. Comparison of Round-to-Nearest-Integer and Round-to-Nearest-Even
Round-to-nearest-integer mode
Round-to-nearest-even mode
6- to 4-bits
Rounding
010111
001101
001010
001110
110111
101101
110110
110010
Table 4–6
lists examples of the difference between the two modes. In this example, a
Round-To-Nearest-Integer
010111
001101
001010
001110
110111
101101
110110
110010
lists how round-to-nearest-even works.
➱
➱
➱
➱
➱
➱
➱
➱
Even (0010)
Even (1100)
Odd (0011)
Odd (1101)
Odd/Even
0110
0011
0011
0100
1110
1011
1110
1101
(Integer)
x
x
x
x
Fractional
> 0.5 (11)
< 0.5 (01)
= 0.5 (10)
= 0.5 (10)
> 0.5 (11)
< 0.5 (01)
= 0.5 (10)
= 0.5 (10)
Chapter 4: DSP Blocks in Stratix IV Devices
Round-To-Nearest-Even
Add to Integer
Stratix IV Operational Mode Descriptions
010111
001101
001010
001110
110111
101101
110110
110010
February 2011 Altera Corporation
1
0
0
1
1
0
1
0
➱
➱
➱
➱
➱
➱
➱
➱
0110
0011
0010
0100
1110
1011
1110
1100
Result
0110
0011
0010
0100
1110
1011
1110
1100