1. Introduction to Verilog Multiplexers

2. Introduction to Verilog Verilog Hardware Description Language (Verilog HDL) released by Gateway Design Automation in 1983 Cadence buys Gateway in 1989 Cadence releases Verilog HDL to the public domain in 1990 Verilog adopted by the IEEE as IEEE standard 1364 in 1995

3. Combinational Circuit Example n-line 2-to-1 Multiplexer n-line 2 x 1 MUX a(n-1:0) b(n-1:0) y(n-1:0) sel sel y 0 a 1 b

4. An n-line 2 x 1 MUX a(n-1:0) b(n-1:0) y(n-1:0) sel n-line 2 x 1 MUX module mux2p(a,b,sel,y); parameter width = 2; input [width-1:0] a; input [width-1:0] b; input sel; output [width-1:0] y; reg [width-1:0] y; always @(sel, a, b) begin if(sel == 0) y = a; else y = b; end endmodule parameter statement defines width of bus

5. module mux2p(a,b,sel,y); parameter width = 2; input [width-1:0] a; input [width-1:0] b; input sel; output [width-1:0] y; reg [width-1:0] y; always @(sel, a, b) begin if(sel == 0) y = a; else y = b; end endmodule module name always sensitivity list Sequential statements (if…else) must be in an always block Note optional begin…end in always block An n-line 2 x 1 MUX reg defines y as a variable

6. module mux2p(a,b,sel,y); parameter width = 2; input [width-1:0] a; input [width-1:0] b; input sel; output [width-1:0] y; reg [width-1:0] y; always @(sel, a, b) begin if(sel == 0) y = a; else y = b; end endmodule Note: = is a blocking assignment An n-line 2 x 1 MUX Note: == is logical equality operator

7. Digilab2 – DIO1 Boards Spartan II FPGA 8 LEDs LD 8 Switches SW 4 Pushbuttons BTN Four 7-segment displays Pushbutton bn 74HC373 latch ldg <= ‘1’

8. Top-level Design – Lab 1

9. module Lab1v(SW,BTN4,ldg,LD); input [1:8] SW; input BTN4; output ldg; output [1:4] LD; mux2p SWmux(.a(SW[1:4]),.b(SW[5:8]),.sel(BTN4),.y(LD)); defparam SWmux.width = 4; assign ldg = 1; // enable 74HC373 latch endmodule

10. module Lab1v(SW,BTN4,ldg,LD); input [1:8] SW; input BTN4; output ldg; output [1:4] LD; mux2p SWmux(.a(SW[1:4]),.b(SW[5:8]),.sel(BTN4),.y(LD)); defparam SWmux.width = 4; assign ldg = 1; // enable 74HC373 latch endmodule

11. module Lab1v(SW,BTN4,ldg,LD); input [1:8] SW; input BTN4; output ldg; output [1:4] LD; mux2p SWmux(.a(SW[1:4]),.b(SW[5:8]),.sel(BTN4),.y(LD)); defparam SWmux.width = 4; assign ldg = 1; // enable 74HC373 latch endmodule Note: assign statement used for concurrent logic equations Note: defparam statement used to override parameter width

13. An n-line 4 x 1 multiplexer a(n-1:0) b(n-1 :0) y(n-1 :0) sel(1:0) n-line 4 x 1 MUX c(n-1 :0) d(n-1 :0) Sely “00”a “01”b “10”c “11”d

14. An n-line 4 x 1 multiplexer module mux4p(a,b,c,d,sel,y); parameter width = 4; input [width-1:0] a,b,c,d; input [1:0] sel; output [width-1:0] y; reg [width-1:0] y; always @(sel, a, b, c, d) case(sel) 0: y = a; 1: y = b; 2: y = c; 3: y = d; default: y = a; endcase endmodule Must include ALL posibilities in case statement Signals can have values 0, 1, z, x sely “00”a “01”b “10”c “11”d Note: default is decimal

15. module Lab1bv(SW,BTN,ldg,LD); input [1:8] SW; input [1:2] BTN; output ldg; output [1:2] LD; mux4p SWmux(.a(SW[1:2]),.b(SW[3:4]),.c(SW[5:6]),.d(SW[7:8]),.sel(BTN),.y(LD)); defparam SWmux.width = 2; assign ldg = 1; // enable 74HC373 latch endmodule Top-level design

16. Verilog Always Block always @( ) begin end Within an always block: Variables (reg) are assigned using = (Blocking) and are updated immediately. (Used for combinational signals) Sequential signals are assigned using <= (Non-blocking) and are updated at the end of the always block.