$display shows unexpected high impedance 'z' output

问题

module hi (
input wire clk,
output wire [6:0] a
);

wire [7:0] b; 
assign b= 8'd24;
assign a[6:0]   = b[7:1];

initial $display ("%d", a);

endmodule

I get a high impedance 'z' output. Where am i going wrong?

回答1:

You didn't give the assign statement a chance to propagate the values on the wires. The initial block executes first. Add a delay before the $display, or use $strobe instead.

来源：https://stackoverflow.com/questions/40035070/display-shows-unexpected-high-impedance-z-output