EP2SGX90EF1152C3 Altera, EP2SGX90EF1152C3 Datasheet - Page 68

• Manufacturer Part Number: EP2SGX90EF1152C3
• Description: Stratix II GX
• Manufacturer: Altera

Adaptive Logic Modules
Figure 2–44. Example of a 3-Bit Add Utilizing Shared Arithmetic Mode
2–60
Stratix II GX Device Handbook, Volume 1
3-Bit Add Example
implemented in adders.
implemented in LUTs.
+
2nd stage add is
1st stage add is
1 1 0 1
1 1 0
+
Binary Add
1 1 0
1 0 1
0 1 0
0 0 1
+
C2 C1 C0
R3 R2 R1 R0
Shared Arithmetic Chain
In addition to the dedicated carry chain routing, the shared arithmetic
chain available in shared arithmetic mode allows the ALM to implement
a three-input add, which significantly reduces the resources necessary to
implement large adder trees or correlator functions. The shared
arithmetic chains can begin in either the first or fifth ALM in a LAB. The
Quartus II Compiler automatically links LABs to create shared arithmetic
chains longer than 16 (8 ALMs in arithmetic or shared arithmetic mode).
For enhanced fitting, a long shared arithmetic chain runs vertically
+
+
Equivalents
Decimal
X2 X1 X0
S2 S1 S0
2 x 6
Y2 Y1 Y0
Z2 Z1 Z0
+
13
6
5
2
1
X0
Y0
Z0
X1
Y1
Z1
X2
Y2
Z2
ALM Implementation
ALM 1
ALM 2
3-Input
3-Input
3-Input
3-Input
3-Input
3-Input
3-Input
3-Input
LUT
LUT
LUT
LUT
LUT
LUT
LUT
LUT
S0
C0
S1
C1
S2
C2
shared_arith_in = '0'
'0'
carry_in = '0'
Altera Corporation
October 2007
R0
R1
R2
R3