1. ASIC 120: Digital Systems and Standard-Cell ASIC Design Tutorial 1: Introduction to Digital Circuits October 11, 2005

2. Outline Digital Systems Combinational Logic –NOT, AND, OR, XOR, NAND, etc. –mux, half-adder, full-adder Sequential Logic –flip-flop/register, shift register, counter –state machines

3. Digital Systems Analog vs. Digital –continuously varying vs. discrete –imprecise vs. precise –0..1 vs. 0 or 1 Digital systems excel at… –repetitive calculations –large amounts of data –reproducible results

4. The Big Picture

6. Combinational and Sequential Logic We can break a digital system into two types of logic Combinational –computation happens in a linear fashion Sequential –computation involves a feedback loop (memory)

7. Combinational Logic: NOT AX 01 10 InputOutput Truth Table

8. Combinational Logic: AND ABX 000 010 100 111

9. Combinational Logic: OR ABX 000 011 101 111

10. Combinational Logic: XOR ABX 000 011 101 110

11. Combinational Logic: NAND ABX 001 011 101 110

12. Combinational Logic: NOR, XNOR ABX 001 010 100 110 ABX 001 010 100 111

13. Building Combinational Circuits ABCX 0000 0100 1001 1101 0010 0111 1010 1111

14. Combinational Logic: MUX (multiplexer) ABCX 0000 0100 1001 1101 0010 0111 1010 1111

15. Half Adder ABSC 0000 0110 1010 1101

16. Full Adder

18. What I’ve Skipped Gates with more than two inputs Boolean algebra Karnaugh maps Quine-McCluskey method Binary arithmetic, base conversions Practical digital circuits have more than 0s and 1s Transmission gates, tri-state buffers

19. Sequential Logic

20. Basic Feedback Element: SR latch SRQQ next 0000 0011 0100 0110 1001 1011 110N/A 111

21. D Flip-Flop or Register DClkQQ next 0000 0011 1000 1011 0 0101 00 0 0101 10 1 0101 01 1 0101 11

22. Synchronous vs. Asynchronous Synchronous –circuit operation governed by a clock –currently more popular and practical Asynchronous –circuit operation independent of a clock –potentially faster than synchronous –lower power consumption –difficult to design

23. Sequential Constructs Shift register Counter State Machines

24. Useful abstract constructs for more complex sequential logic

25. What I’ve Skipped Other flip-flops (RS, T, JK) Other interesting sequential circuits (barrel shifters, etc.)

26. Hardware Description Languages (HDLs) HDL describes in text a digital circuit Examples –VHDL (we will look at this next time) –Verilog –AHDL –JHDL

27. Hardware Description Languages (HDLs) schematics are useful for… –drawing high level diagrams –manually working out simple pieces of logic HDLs are useful for… –describing complex digital systems HDLs are not... –software programming languages (C, Java, assembly, etc.)

28. Summary Digital Systems Combinational Logic –NOT, AND, OR, XOR, NAND, etc. –mux, half-adder, full-adder Sequential Logic –flip-flop/register, shift register, counter –state machines

29. UW ASIC Design Team www.asic.uwaterloo.ca reference material –Bryce Leung’s tutorials (UW ASIC website) –Michael Goldsmith’s tutorials (UW ASIC website) –your course notes my contact info: Jeff Wentworth, jswentwo@engmail.uwaterloo.ca