EP1C12 查看數據表（PDF） - Unspecified

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EP1C12

Cyclone FPGA Family

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Preliminary Information

Cyclone FPGA Family Data Sheet

addnsub Signal

The LE’s dynamic adder/subtractor feature saves logic resources by using

one set of LEs to implement both an adder and a subtractor. This feature

is controlled by the LAB-wide control signal addnsub. The addnsub

signal sets the LAB to perform either A + B or A − B. The LUT computes

addition; subtraction is computed by adding the two’s complement of the

intended subtractor. The LAB-wide signal converts to two’s complement

by inverting the B bits within the LAB and setting carry-in = 1 to add one

to the least significant bit (LSB). The LSB of an adder/subtractor must be

placed in the first LE of the LAB, where the LAB-wide addnsub signal

automatically sets the carry-in to 1. The Quartus II Compiler

automatically places and uses the adder/subtractor feature when using

adder/subtractor parameterized functions.

LE Operating Modes

The Cyclone LE can operate in one of the following modes:

■ Normal mode

■ Dynamic arithmetic mode

Each mode uses LE resources differently. In each mode, eight available

inputs to the LEthe four data inputs from the LAB local interconnect,

carry-in0 and carry-in1 from the previous LE, the LAB carry-in

from the previous carry-chain LAB, and the register chain

connectionare directed to different destinations to implement the

desired logic function. LAB-wide signals provide clock, asynchronous

clear, asynchronous preset/load, synchronous clear, synchronous load,

and clock enable control for the register. These LAB-wide signals are

available in all LE modes. The addnsub control signal is allowed in

arithmetic mode.

The Quartus II software, in conjunction with parameterized functions

such as library of parameterized modules (LPM) functions, automatically

chooses the appropriate mode for common functions such as counters,

adders, subtractors, and arithmetic functions. If required, the designer can

also create special-purpose functions that specify which LE operating

mode to use for optimal performance.

Altera Corporation

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