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AN INTRODUCTION TO VHDL

Designing Hardware with Software

by James Antonakos

Start ý Levels of Design ý The Interface ý The Body ý Full_Adder ý Half _Adder ý Identifiers, Data Types, and Operators ý Examples ý The Five-Input AND Gate ý The 2:4 Decoder ý Timing Examples ý Other Methods ý Sources and PDF

LEVELS OF DESIGN

VHDL designs may contain one or more levels, as indicated by the 4-bit ripple adder structure shown in Figure 2. The top level (system) contains the least amount of detail regarding the actual hardware implementation. The bottom level (gates) contains the actual logic gates used to implement the system.

Figure 2ýA multilevel design hierarchy detailing components of a full adder is used in VHDL designs.

The design method of starting with the topmost level and adding new levels of increasing detail is called top-down design. Letýs start with the design of a 4-bit ripple adder, beginning with the topmost level.

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