Welcome to the National Instruments presentation of the Spartan-3E Starter Board as an academic learning platform. Understanding digital logic and FPGA concepts can be daunting for some undergraduate students, especially those not studying electrical engineering. To facilitate a long-term and engaging learning environment, there is a need for an intermediary hardware and software package that is cost-effective, easy to understand and to implement, and is adaptable with existing VHDL code.
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Welcome to the National Instruments presentation of the ...download.ni.com/pub/devzone/tut/spartan_3e_labview_fpga.pdfexisting VHDL code. ... Using NAND gates for combination logic
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Welcome to the National Instruments presentation of the Spartan-3E Starter Board as an
academic learning platform.
Understanding digital logic and FPGA concepts can be daunting for some undergraduate
students, especially those not studying electrical engineering. To facilitate a long-term and
engaging learning environment, there is a need for an intermediary hardware and software
package that is cost-effective, easy to understand and to implement, and is adaptable with
existing VHDL code.
Digital Design Fundamentals
The NAND gate is the fundamental building block for digital logic. It is a combination of
an AND gate coupled with a NOT gate at its output. The truth table above describes the
output behavior of implementing a NAND gate on two bitwise inputs.
Digital Design Fundamentals
NAND gates can be used in combination to implement logic that would traditionally be
implemented with AND, OR, and NOT gates. Using NAND gates for combination logic is
cost effective due to its logical completeness and inherent compactness.
The figure to the top left shows a basic combination logic. The figure to the bottom left
shows the same logic implemented using only NAND gates. Finally, the figure to the top
right shows an equivalent combination logic after logic optimizations are performed.
Single Bit Adders: Half Adder
To create even more complex combinational logic, truth tables can be used to describe implementation. For example, a half adder is a logic circuit that can perform an addition on two binary digits. The half adder produces a sum and a carry value which are both binary digits.
Although logically concise, the half-adder cannot carry bits in multi-bit addition operations which is considered a drawback.