some questions about Verilog from beginner:)

[Altera_Forum]

Hi everyone! 

 Just started to learn Verilog language. Meet the problem in my first more or less serious project. Can you explain me please what does -1:0 mean in:   input [input_width-1:0] x;   and what is the difference between this and, for example, input [input_width+2:0] x;   Also would be grateful if someone explains what does DLY_WIDTH means in this code: (butterworth IIR example):   parameter INPUT_WIDTH = 12;   parameter COEF_WIDTH = 10;   parameter DLY_WIDTH = 18;   parameter F_BITS = 4; // fractional bits   parameter OUTPUT_WIDTH = 21;   parameter L_BIT = 10 ; // low bit   parameter H_BIT = 30; // high bit   // parameter L_BIT = COEF_WIDTH ; // low bit   // parameter H_BIT = L_BIT + OUTPUT_WIDTH - 1; // high bit     //Port Declaration   input clk;   input clken;   input reset;   // input [INPUT_WIDTH-1:0] x;   // output [OUTPUT_WIDTH-1:0] result; //SBF 17.4   input [11:0] x;   output [20:0] result; //SBF 17.4     //Wire Declaration   wire [OUTPUT_WIDTH-1:0] out_biquad1;   wire [F_BITS-1:0] pzeros;   wire [DLY_WIDTH-1:0] xn;   wire [OUTPUT_WIDTH-1:0] result_w;   wire [COEF_WIDTH-1:0] iir_gain;   wire [OUTPUT_WIDTH+COEF_WIDTH-1:0] gain_out;       //Reg Declaration   reg [DLY_WIDTH-1:0] xn_reg;   // reg [OUTPUT_WIDTH-1:0] result;   reg [20:0] result;   reg [DLY_WIDTH-1:0] in_biquad2;     assign pzeros = 0;   assign iir_gain = GAIN;   assign xn = {x[INPUT_WIDTH-1], x[INPUT_WIDTH-1], x[INPUT_WIDTH-1:0], pzeros[F_BITS-1:0]}; // SBF 14.4     Hope you can help me:) Alex

[Altera_Forum]

INPUT_WIDTH and other parameters are simply constant definitions which allow you to easily manage code in case you need to change the value. If you are familiar with C programming, these are similar to a# define 

So, if you have defined INPUT_WIDTH = 12, like in your sample code,   input [INPUT_WIDTH-1:0] x;  is exactly the same as   input [11:0] x;  and [INPUT_WIDTH+2:0] x;  is the same as input [14:0] x;  If you want to change width from 12 to 16, you only modify the parameter line and you don't need to keep track of all the places where that value is involved.

[Altera_Forum]

And just to be clear in case you are real new. 

 "x" is the name of a signal that come into the chip and [] is telling the code that it is a group of signals, not one signal.  The value 11:0 (as expalined before) means signals named; x11, x10, x9, ... x1, x0 (12 elements) - so this is a bus or signals into the design, a vector.  You may already get that part - but I though I wold be real complete for you (and others who read this).