ASIC 121: Practical VHDL Digital Design for FPGAs

ASIC 121: Practical VHDL Digital Design for FPGAs Tutorial 1 September 27, 2006

Contributions • I have taken some of the slides in this tutorial from Jeff Wentworth’s ASIC 120

Digital vs Analog • Analog: Continuous time varying signal. • Application: Radio • Digital: Abstraction. Two signals: 0 and 1. • Application: Computer Processors

Switches • Switches are the basic building block of Digital hardware • Have 2 states: • On = 1, Off = 0 • Can be electrically controlled: • Ex. Relay, Vacuum Tube, Transistor

A Wires Transistor C B Transistor • Used in all modern digital hardware • 3 Terminal Device • Operation: • If C is high voltage (1) then current flows between A and B

Logic Gates • 2-input, 1-output devices • Simpler than working with switches directly • Inverter (NOT gate): Input Output Truth Table

5 V (1) Transistor 1 Output Input Transistor 2 Ground (0) Inverter Implementation • When Input is 1: • Transistor 1: off • Transistor 2: on • Output: 0 (ground) • When Input is 0: • Transistor 1: on • Transistor 2: off • Output: 1 (5V)

Combinational Logic: AND

Combinational Logic: OR

Combinational Logic: XOR

Combinational Logic: NAND

Combinational Logic: NOR, XNOR

Building Combinational Circuits

Combinational Logic: MUX(multiplexer)

MUXs • A MUX can be thought of as an if statement. If C = 0 then X = A Else if C = 1 then X = B • This will be useful later

Binary Addition • Adding 2 bits: • 0+0=0 • 0+1=1 • 1+0=1 • 1+1=10 • So we need 2 inputs and 2 outputs

Half Adder

Full Adder (3-bit addition)

Independent Tasks • Modelsim – VHDL hardware simulator • Download evaluation copy from: http://www.model.com/downloads/evaluations.asp • Quartus II – FPGA Synthesis Tool • Download Web Edition from: http://www.altera.com/products/software/products/quartus2web/sof-quarwebmain.html

Development Boards • For interested students there are development boards available • Check out the DE2: http://www.altera.com/education/univ/materials/boards/unv-de2-board.html • The DE2 comes with lab exercises and design examples • Not cheap: $269 US

Quartus II Exercise • Open Quartus II, Select File->New Project Wizard, Select a valid working directory (should be an empty folder) • Name the project and entity “half_adder” • Click next for all other menus • Select File->New. Select VHDL File

Quartus II Exercise Cont • Save the file as half_adder.vhd, with the contents: library ieee; use ieee.std_logic_1164.all; entity half_adder is Port ( i_A, i_B : in STD_LOGIC; o_Sum, o_Carry : out STD_LOGIC ); end half_adder; architecture main of half_adder is begin o_Sum <= i_A xor i_B; o_Carry <= i_A and i_B; end main;

Quartus II Exercise Cont • Select Processing->Start->Analysis and Synthesis • Make sure it completes successfully • Next Step • Read through the help file under “simulation” • Try Simulating the design

ASIC 121: Practical VHDL Digital Design for FPGAs