Adaptive Logic Modules
Figure 2–13. ALM in Shared Arithmetic Mode
shared_arith_in
carry_in
4-Input
LUT
To general or
local routing
To general or
local routing
D
Q
datae0
datac
datab
dataa
reg0
4-Input
LUT
4-Input
LUT
To general or
local routing
datad
datae1
To general or
local routing
D
Q
4-Input
LUT
reg1
carry_out
shared_arith_out
Note to Figure 2–13:
(1) Inputs dataf0and dataf1are available for register packing in shared arithmetic mode.
Adder trees can be found in many different applications. For example, the
summation of the partial products in a logic-based multiplier can be
implemented in a tree structure. Another example is a correlator function
that can use a large adder tree to sum filtered data samples in a given time
frame to recover or to de-spread data which was transmitted utilizing
spread spectrum technology.
An example of a three-bit add operation utilizing the shared arithmetic
mode is shown in Figure 2–14. The partial sum (S[2..0])and the
partial carry (C[2..0])is obtained using the LUTs, while the result
(R[2..0])is computed using the dedicated adders.
2–18
Stratix II Device Handbook, Volume 1
Altera Corporation
May 2007
ALTERA [ ALTERA CORPORATION ]
