nand.v
/*
Nand(a, b) : If a = b = 1 then out = 0 else out = 1
*/
// gate-level
module nand_gate (output out, input a, b);
// wire : internal pin
wire w;
// operations
and(w, a, b);
not(out, w);
endmodule
// behavioural-level
module nand_behavioural (output reg out, input a, b);
always @ (a or b) begin
// note: 1'b : 1 bit
if (a == 1'b1 & b == 1'b1) begin
out = 1'b0;
end
else begin
out = 1'b1;
end
end
endmodule
// test
module test;
reg a, b;
wire out;
// nand_gate Instance0 (out, a, b);
nand_behavioural Instance0 (out, a, b);
// note: #(n) : delay by n timestep (check time scale with $printtimescale)
initial begin
#(0) a = 0; b = 0; // 1
#(1) a = 0; b = 1; // 1
#(1) a = 1; b = 0; // 1
#(1) a = 1; b = 1; // 0
end
initial begin
$printtimescale;
// Time scale of (_nand_test) is 1s / 1s
$monitor ("%1d | a = %d | b = %d | out = %d", $time, a, b, out);
// 0 | a = 0 | b = 0 | out = 1
// 1 | a = 0 | b = 1 | out = 1
// 2 | a = 1 | b = 0 | out = 1
// 3 | a = 1 | b = 1 | out = 0
end
endmodule