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# 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

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## ASIC 121: Practical VHDL Digital Design for FPGAs

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

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

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

4. 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

5. 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

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

7. 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)

8. Combinational Logic: AND

9. Combinational Logic: OR

10. Combinational Logic: XOR

11. Combinational Logic: NAND

12. Combinational Logic: NOR, XNOR

13. Building Combinational Circuits

14. Combinational Logic: MUX(multiplexer)

15. 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

16. 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