Chapter 7:VHSIC Hardware Description Language.

Lecture 7: VHDL - Introduction.PPTX

1. Unit 7: VHDL

2. Basics of VHDL • VHDL stands for VHSIC Hardware Description Language. • Used to model digital systems at multiple levels (behavioral, RTL, structural). • Key Elements: - Entity: Defines inputs/outputs. - Architecture: Defines functionality. - Library & Package: Provide reusable components.

3. RTL Design & Combinational Logic • RTL: Register Transfer Level – describes data transfer between registers. • Combinational Logic: Output depends only on inputs. • Example: Half Adder in VHDL ENTITY HalfAdder IS PORT(A, B: IN BIT; SUM, CARRY: OUT BIT); END HalfAdder ; ARCHITECTURE Logic OF HalfAdder IS BEGIN SUM <= A XOR B; CARRY <= A AND B; END Logic;

4. Types, Operators, and Packages • Types: BIT, BOOLEAN, INTEGER, STD_LOGIC, etc. • Operators: AND, OR, NOT, XOR, +, -, *, / • Packages: Collections of functions, procedures, and types. • Example: Using IEEE.STD_LOGIC_1164 for logic operations.

5. Sequential Circuits & Subprograms • Sequential Circuits: Depend on present input and past states. • Example: D Flip-Flop in VHDL PROCESS(CLK) BEGIN IF rising_edge (CLK) THEN Q <= D; END IF; END PROCESS; • Subprograms: Functions and Procedures. - Function: Returns a single value. - Procedure: Can return multiple values.

6. Examples of VHDL Circuits • Adders: Half Adder, Full Adder. • Counters: Binary counter using process & clock. • Flip-Flops: SR, JK, D, T Flip-Flops. • Multiplexers: Select input based on control. • Demultiplexers: Route input to one output line. • Each circuit can be implemented in behavioral, dataflow, or structural modeling style.