ep2sgx30c Altera Corporation, ep2sgx30c Datasheet - Page 64

• Manufacturer Part Number: ep2sgx30c
• Description: Stratix Ii Gx Device Data Sheet
• Manufacturer: Altera Corporation

Adaptive Logic Modules
Figure 2–41. ALM in Arithmetic Mode
2–56
Stratix II GX Device Handbook, Volume 1
datae0
datae1
dataf0
dataf1
datab
dataa
datad
datac
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
Figure
R = (X < Y) ? Y : X
To implement this function, the adder is used to subtract ‘Y’ from ‘X’. If
‘X’ is less than ‘Y’, the carry_out signal will be ‘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.
4-Input
4-Input
4-Input
4-Input
2–42. The equation for this example is:
LUT
LUT
LUT
LUT
carry_out
carry_in
adder0
adder1
D
D
reg0
reg1
Q
Q
To general or
To general or
To general or
To general or
local routing
local routing
local routing
local routing
Altera Corporation
October 2007