EP2AGX95EF29C6N Datasheet, PDF (41/380 Pages) Altera Corporation – Device Interfaces and Integration

Chapter 2: Logic Array Blocks and Adaptive Logic Modules in Arria II Devices
Adaptive Logic Modules
2–11
Arithmetic Mode
Arithmetic mode is ideal for implementing adders, counters, accumulators, wide
parity functions, and comparators. The ALM in arithmetic mode uses two sets of two
4-input LUTs along with two dedicated full adders. The dedicated adders allow the
LUTs to be available to perform pre-adder logic; therefore, each adder can add the
output of two 4-input functions. The four LUTs share dataa and datab inputs. As
shown in Figure 2–10, the carry-in signal feeds to adder0 and the carry-out from
adder0 feeds to the carry-in of adder1. The carry-out from adder1 drives to adder0 of
the next ALM in the LAB. ALMs in arithmetic mode can drive out registered and
unregistered versions of the adder outputs.
Figure 2–10. ALM in Arithmetic Mode
carry_in
datae0
dataf0
datac
datab
dataa
4-Input
LUT
4-Input
LUT
adder0
DQ
reg0
To general or
local routing
To general or
local routing
datad
datae1
dataf1
4-Input
LUT
4-Input
LUT
adder1
DQ
reg1
To general or
local routing
To general or
local routing
carry_out
In arithmetic mode, the ALM supports simultaneous use of the adder’s carry output
along with combinational logic outputs. The adder output is ignored in this operation.
Using the adder with combinational logic output provides resource savings of up to
50% for functions that can use this mode.
Arithmetic mode also offers clock enable, counter enable, synchronous up and down
control, add and subtract control, synchronous clear, and synchronous load. The LAB
local interconnect data inputs generate the clock enable, counter enable, synchronous
up and down, and add and subtract control signals. These control signals are good
candidates for the inputs that share the four LUTs in the ALM. The synchronous clear
and synchronous load options are LAB-wide signals that affect all registers in the
LAB. These signals can also be individually disabled or enabled per register. The
Quartus II software automatically places any registers that are not used by the counter
into other LABs.
December 2010 Altera Corporation
Arria II Device Handbook Volume 1: Device Interfaces and Integration