EP2S15 ALTERA [Altera Corporation], EP2S15 Datasheet - Page 23

• Manufacturer Part Number: EP2S15
• Description: Stratix II Device Family
• Manufacturer: ALTERA [Altera Corporation]

Altera Corporation
May 2007
Figure 2–11. ALM in Arithmetic Mode
While operating in arithmetic mode, the ALM can support simultaneous
use of the adder's carry output along with combinational logic outputs. In
this operation, the adder output is ignored. This usage of the adder with
the combinational logic output provides resource savings of up to 50% for
functions that can use this ability. An example of such functionality is a
conditional operation, such as the one shown in
equation for this example is:
To implement this function, the adder is used to subtract ‘Y’ from ‘X.’ If
‘X’ is less than ‘Y,’ the carry_out signal is ‘1.’ The carry_out signal is
fed to an adder where it drives out to the LAB local interconnect. It then
feeds to the LAB-wide syncload signal. When asserted, syncload
selects the syncdata input. In this case, the data ‘Y’ drives the
syncdata inputs to the registers. If ‘X’ is greater than or equal to ‘Y,’ the
syncload signal is de-asserted and ‘X’ drives the data port of the
registers.
datae0
datae1
dataf0
dataf1
datab
dataa
datad
datac
R = (X < Y) ? Y : X
4-Input
4-Input
4-Input
4-Input
LUT
LUT
LUT
LUT
carry_out
carry_in
Stratix II Device Handbook, Volume 1
adder0
adder1
D
D
reg0
reg1
Figure
Q
Q
Stratix II Architecture
2–12. The
To general or
To general or
To general or
To general or
local routing
local routing
local routing
local routing
2–15