ECT 358

1. ECT 358 Lecture 5 Introduction to Verilog 1

2. Although the tongue weighs very little, few people are able to hold it. Even so the tongue is a little member, and boasteth great things. Behold, how great a matter a little fire kindleth. James 3:5

3. Hardware Description Languages • VHLIC HDL (VHDL) • Verilog HDL • AHDL • Parts • Text Based Description • Compiler • Simulator

4. Verilog HDL • Top Down Design • Schematic Entry (Structural Description) • Truth Table • Boolean Entry (Functional Description) • Text Description (Behavioral Description) • Exported to Multiple Platforms and Designs

5. Verilog Module Format moduledesign_name(port_list); … // Declarations of ports … //Functional details endmodule • Syntax is similar to C. • Comments denoted by // or /* … */ • Statements end in semi-colon. • Variable names are case sensitive. • White space is ignored (SPACE, TAB, new-line) • Functionality • Ports • Timing Constraints • No required order to port list

6. Verilog Structural Primitives • The basic functional objects of logic gates • Outputs Followed by Inputs Multiple Inputs – Single Outputs and, nand, or, nor, xor, xnor Multiple Outputs – Single Inputs buf, not Tri-State Multiple Outputs bufif0, bufif1, notif0, notif1

7. Verilog Ports • Input • Output • Inout module half_adder(a,b,sum,cout); input a, b; output sum, cout; andg1(cout,a,b); xorg2(sum,a,b); endmodule

8. prim A F B Verilog Wires • Wire is an internal connection between primitives module prim(A,B,F); input A, B; output F; wire w; not (w,B); and (F,A,w); endmodule wire

9. Verilog Nets • net_kind [msb:lsb ] net1,net2, ….net N; • net_kind is either wire or tri • msb and lsb are constant expressions that specify the range of the net • If no range is specified, range defaults to one bit • Examples wire clk, a, b; // Three one-bit wire nets wire [3:0] A, B; // Two four-bit wire nets wire [range-1:0] busA //a parameterized net declaration • tri nets have same declaration form as wire nets • Use tri nets when multiple drivers drive a net

10. Language Rules • Case Sensitive My_input vs. my_input • Space Free • Upper and Lower case letters • Digits • Underscore • Dollar Sign • Variable cannot begin with Number or $ • Reserved Keywords • Vectors indicate more than one wire sum[3:0]

11. Other Module Functionality • Register reg B[3:0]; //store values • Parameter parameter size=8; • Assign assign name = A && B; • Pullup pullup (out_y); • Pulldown pulldown (out_x);

12. Assignments • Blocking B = A; C = B; D = C; //A=B=C=D • Non-Blocking B <= A; C <= B; D <= C; //shift

13. Signal Levels

14. Radix’s Radix Description d decimal b binary h hexadecimal o octal 0 the number 0 10 the decimal number 10 ′b10 the binary number 10 ′h10 the hex number 10 4′ b100 the binary number 0100 8′b1000_0011 underscore _ can be inserted for readability 8′hfx equivalent to 8′b1111_xxxx

15. Nested Modules module halfadder (sum, c_out, a, b); input a, b; output sum, c_out; xor (sum, a, b); and (c_out, a, b); endmodule

16. Nested Modules module fulladder (sum, c_out, a, b, c_in); input a, b, c_in; output sum, c_out; wire w1, w2, w3; halfadder HA1(w1, w2, a, b); halfadder HA2(sum, w3, c_in, w1); or (c_out, w2, w3); endmodule

17. Truth Table Models primitive my_table(y,x1,x2,x3); output y; input x1,x2,x3; table // x1 x2 x3 : y 0 0 0 : 1; 0 0 1 : 0; 0 1 0 : 1; 0 0 1 : 1; 1 0 0 : 1; 1 0 1 : 0; 1 1 ? : 1; endtable endprimitive // ? Includes 0, 1, and x