ep1sgx25d Altera Corporation, ep1sgx25d Datasheet - Page 73

• Manufacturer Part Number: ep1sgx25d
• Description: Stratix Gx Device Family Data Sheet
• Manufacturer: Altera Corporation

Altera Corporation
February 2005
Dynamic Arithmetic Mode
The dynamic arithmetic mode is ideal for implementing adders, counters,
accumulators, wide parity functions, and comparators. An LE in dynamic
arithmetic mode uses four 2-input LUTs configurable as a dynamic
adder/subtractor. The first two 2-input LUTs compute two summations
based on a possible carry-in of 1 or 0; the other two LUTs generate carry
outputs for the two chains of the carry select circuitry. As shown in
Figure
carry-in1 chain. The selected chain’s logic level in turn determines
which parallel sum is generated as a combinatorial or registered output.
For example, when implementing an adder, the sum output is the
selection of two possible calculated sums: data1 + data2 + carry-in0
or data1 + data2 + carry-in1. The other two LUTs use the data1 and
data2 signals to generate two possible carry-out signals—one for a carry
of 1 and the other for a carry of 0. The carry-in0 signal acts as the carry
select for the carry-out0 output and carry-in1 acts as the carry select
for the carry-out1 output. LEs in arithmetic mode can drive out
registered and unregistered versions of the LUT output.
The dynamic arithmetic mode also offers clock enable, counter enable,
synchronous up/down control, synchronous clear, synchronous load,
and dynamic adder/subtractor options. The LAB local interconnect data
inputs generate the counter enable and synchronous up/down control
signals. The synchronous clear and synchronous load options are
LAB-wide signals that affect all registers in the LAB. The Quartus II
software automatically places any registers that are not used by the
counter into other LABs. The addnsub LAB-wide signal controls
whether the LE acts as an adder or subtractor.
4–6, the LAB carry-in signal selects either the carry-in0 or
Stratix GX Device Handbook, Volume 1
Stratix GX Architecture
4–7