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Introduction to HDLs

Introduction to HDLs. HDL (Hardware Description Language) VHDL versus Verilog IC world only uses Verilog. How do IC designers use Verilog?. Can be used for simulation Simulation at behavioral level, gate level, and at the switch level! Can be used for circuit synthesis

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Introduction to HDLs

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  1. Introduction to HDLs • HDL (Hardware Description Language) • VHDL versus Verilog • IC world only uses Verilog

  2. How do IC designers use Verilog? • Can be used for simulation • Simulation at behavioral level, gate level, and at the switch level! • Can be used for circuit synthesis • Can be used to verify post-synthesis timing

  3. Why Verilog and not VHDL? • C-like syntax (as opposed to Pascal-like!) • Better for circuit synthesis • I feel it is easier to create testbenches but others will dispute this claim! • Switch-level descriptions supported • Timing is more easily included • Can link in you own C-code!

  4. Verilog Coding Styles • Behavioral Descriptions • Dataflow Descriptions • Gate-Level Descriptions (netlist) • Switch-Level Descriptions

  5. Verilog Basics • Case-sensitive!!!!! • No special characters in variable names except _ • Variable names must start with alpha character • Free-form • Very C-like

  6. Concurrent Versus Sequential • Separate syntax to support descriptions of concurrent and sequential activity • Concurrent constructs best for describing combinational circuits • Sequential constructs must be used for describing sequential networks and for writing testbenches … MAY be used for combinational circuits BUT BE CAREFUL!

  7. First Example // // First example // module first_example(f, x, y, z) ; input x, y, z ; output f ; assign f = (x & y & ~z) | (x & ~y & z) | (~x & ~y & ~z) ; endmodule

  8. First Example Testbench // // Testbench for first example // `timescale 1ns/100ps module first_example_tb ; reg x, y, z ; wire f ; integer fid ; first_example u0(f, x, y, z) ; initial begin fid = $fopen("./first_example.out") ; $fmonitor(fid, $time, " x = %b, y = %b, z = %b, f = %b", x, y, z, f) ; #100 x = 1'b0 ; y = 1'b0 ; z = 1'b0 ; #100 x = 1'b1 ; y = 1'b1 ; z = 1'b0 ; #100 x = 1'b1 ; y = 1'b1 ; z = 1'b1 ; #100 $finish ; end endmodule

  9. Running Verilog XL To simulate “first example” do the following: % verilog first_example_tb.v first_example.v OR Create a file called, for example, “modules” and on separate Lines place the two filenames from above and give the Command % verilog –f modules

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