l9_handouts_4up - Announcements ECE 3140/CS 3420 Computer Organization Spring S i 2009 Sequential Digital Logic g g Project 2 Due Tue Feb 21 at 10:00pm

1 ECE 3140/CS 3420 Computer Organization S i 2009 Spring 2009 Sequential Digital Logic ECE3140/CS3420 Announcements • Project 2 – Due Tue, Feb 21 at 10:00pm ECE3140/CS3420 2 Hennessy and Patterson • Read Chapter 1 – 1.1-1.9 • Read Chapter 2 Read Chapter 2 – 2.1 through 2.14 – MIPS Calling Convention Document (website) – Notes on Programming in C (website) • Read Chapter 3 – 3.1 through 3.2 – 3.3 through 3.5 (for Tuesday) ECE3140/CS3420 3.3 through 3.5 (for Tuesday) • Read Appendices C – B.1-B.6, B.10, C.1-C.10 3 Today’s Topic • Digital Logic – Sequential • Verilog Hardware Modeling – How to implement digital logic using a HDL – Verilog syntax/details to be covered in section ECE3140/CS3420 4

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2 Sequential Circuits • The output of a sequential circuit depends on current inputs and past inputs – I.e., circuit “remembers” past events • Idea: – Introduce devices that can hold state • Called state-holding elements (e.g., flip-flops) – Next state depends on previous state (stored in stat- holding elements) and circuit inputs – Outputs depend on previous state and circuit inputs ECE3140/CS3420 Outputs depend on previous state and circuit inputs – Next state and outputs calculated using combinational circuits 5 State Machine Structure Combinational Logic inputs outputs next state current state ECE3140/CS3420 State Memory clock 6 D Flip-flops • A flip-flop is a 1-bit memory – Stores 1 bit of “state” information – Changes state on each “tick of the clock” • Positive edge-triggered flip-flops D CLK Q QN 0 ↑ 0 1 ECE3140/CS3420 0 0 1 1 ↑ 1 0 x 0 last Q last QN x 1 last Q last QN x ↓ last Q last QN D Q QN 7 D Flip-Flops • Negative edge-triggered flip-flops D CLK Q QN 0 ↓ 0 1 D Q • Positive edge-triggered FF’s with enable 1 ↓ 1 0 x 0 last Q last QN x 1 last Q last QN x ↑ last Q last QN QN D Q D EN CLK Q QN 0 1 ↑ 0 1 1 1 ↑ 1 0 ECE3140/CS3420 QN EN 1 x 0 ↑ last Q last QN x x 0 last Q last QN x x 1 last Q last QN x x ↓ last Q last QN 8