EP1C20F ALTERA [Altera Corporation], EP1C20F Datasheet - Page 15

• Manufacturer Part Number: EP1C20F
• Description: Cyclone FPGA Family
• Manufacturer: ALTERA [Altera Corporation]

Altera Corporation
May 2008
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:
or
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.
data1 + data2 + carry-in0
data1 + data2 + carry-in1
2–7, the LAB carry-in signal selects either the carry-in0 or
Logic Elements
Preliminary
2–9