How to compare a re-writable 4 bit value to a given 4 bit input in Verilog?

Question

The goal of this project to design a computational lock alarm in Verilog to be run on an Altera board (note on the board 0 is actually ON and 1 is OFF).

Based on the design criteria I created a state diagram of all possible states and contained them into a "cases" statement in my verilog code.

However, I'm having trouble comparing the inputted combination code and the registered password and ALSO rewriting a new password to the registered password when the design is in a particular state.

Note that I've included many of my troubles in comment blocks/lines.

/* NOTES: FIX THE PASSWORD REGISTER AND INPUTS*/

module combinationalLock (clock, INPUTS, enter, change, reset, door, newPass, alarm);

    input enter, change, reset;
    input [4:1] INPUTS; // I don't know if I've defined this correctly

    output door, newPass, alarm;

    reg[3:1] y, Y;

    wire[4:1] passwordREG; // rewritable and comparable to INPUTS (I don't know if I've defined this correctly)
    parameter[3:1]

    // Binary state values

    START = 3'b000, 
    AGAIN = 3'b001, 
    ALARM = 3'b010, 
    CHANGE_OLD = 3'b011, 
    OPEN_DOOR = 3'b100, 
    CHANGE_OLD_AGAIN = 3'b101, 
    CHANGE_NEW = 3'b110;

    // Default password combo

   passwordREG = 4'b0110; // IM TRYING TO SET THE DEFAULT PASSWORD HERE

    // State conditions and changes

    always @(INPUTS, y, reset, change, enter)

        case(y)

            START: if((enter == 0) && (/*INPUTS ARE EQUAL TO REGISTRED PASSWORD*/)) Y = OPEN_DOOR;
                     else if ((enter == 0) && (/*INPUTS ARE NOT EQUAL TO REGISTRED PASSWORD*/)) Y = AGAIN;
                     else Y = START;

            AGAIN: if((enter == 0) && (/*INPUTS ARE EQUAL TO REGISTRED PASSWORD*/)) Y = OPEN_DOOR;
                     else if ((enter == 0) && (INPUTS != passwordREG)) Y = ALARM;
                     else Y = AGAIN;

            ALARM: if(reset == 0) Y = CHANGE;
                     else Y = ALARM;

            CHANGE_OLD: passwordREG = 4'b0110;
                            if((change == 0) && (/*INPUTS ARE EQUAL TO REGISTRED PASSWORD*/)) Y = CHANGE_NEW;
                          else if ((change == 0) && (/*INPUTS ARE NOT EQUAL TO REGISTRED PASSWORD*/)) Y = CHANGE_OLD_AGAIN;
                          else Y = CHANGE_OLD;

            OPEN_DOOR: if(enter == 0) Y = START;
                         else Y = OPEN_DOOR;

            CHANGE_OLD_AGAIN: if((change == 0) && (/*INPUTS ARE EQUAL TO REGISTRED PASSWORD*/)) Y = CHANGE_NEW;
                                else if ((change == 0) && (/*INPUTS ARE NOT EQUAL TO REGISTRED PASSWORD*/)) Y = ALARM;
                                else Y = CHANGE_OLD_AGAIN;

            CHANGE_NEW: passwordREG = INPUTS; // NOTE IN THIS LINE IM TRYING TO REWRITE THE REGISTERED PASSWORD
                            if((CHANGE == 0)||(ENTER == 0)) Y = START; 
                          else Y = CHANGE_NEW;

            default: Y = 3'bxxx;

        endcase

    // Clock pulse

    always @(posedge clock)
        y<=Y;

    // Output

    assign door = (y == OPEN_DOOR);
    assign newPass = (y == CHANGE_NEW);
    assign alarm = (y == ALARM);


endmodule 

Note: I'm also getting some odd syntax errors at line 27, 47, and 59 where they expect an "end case".

Answer 1

A few points to make.

Firstly for Verilog you should be using zero-indexing. e.g. wire [3:0] imAFourBitWire.

---

Second, if the body of a case statement takes up more than one line, you need to wrap it in begin-end statements (in fact liberal use of this is a good habit to get into). E.g.

case(y)
   SOMETHING: begin
      aThing = bThing;
      cThing = anotherThing;
   end
   ...
endcase

Notice how multi-line is wrapped in begin-end.

The same goes for if and if-else statements. Yes you can omit the begin-end, but it doesn't mean you should, especially if you are starting out with the language. It doesn't take long to add 8 characters, but it makes the code structure far easier to follow.

---

Thirdly, this line:

passwordREG = 4'b0110; // IM TRYING TO SET THE DEFAULT PASSWORD HERE

You need to use an assign statement if you want to assign a value to a wire.

---

This then leads on to:

passwordREG = INPUTS; // NOTE IN THIS LINE IM TRYING TO REWRITE THE REGISTERED PASSWORD

But you declared passwordREG as a wire, not a reg. You are violating two rules here:

1. You cannot assign a value to a wire with a procedural assignment (e.g. = in an always block), only using continuous assignment (assign statements)
2. You can only assign a wire with more than one assignment. You've already got passwordREG = 4'b0110; further up.

---

Next, using parameter[3:1] is no different from parameter. Setting the width of a parameter like this has no effect. Instead the width is the width of whatever value you are setting - e.g. parameter something=3'b110 would create a 3-bit parameter.

---

Finally, again from a stylistic standpoint, while you can declare multiple parameters like you've done, i.e.

parameter[3:1]

// Binary state values

START = 3'b000, 
AGAIN = 3'b001, 
ALARM = 3'b010, 
CHANGE_OLD = 3'b011, 
OPEN_DOOR = 3'b100, 
CHANGE_OLD_AGAIN = 3'b101, 
CHANGE_NEW = 3'b110;

I would advise not doing so, it makes the code harder to follow and mistakes can start to creep in. Instead use:

// Binary state values

parameter START = 3'b000;
parameter AGAIN = 3'b001; 
parameter ALARM = 3'b010; 
parameter CHANGE_OLD = 3'b011;
parameter OPEN_DOOR = 3'b100; 
parameter CHANGE_OLD_AGAIN = 3'b101;
parameter CHANGE_NEW = 3'b110;

It doesn't add much more in the way of effort, but it will some day save you a load of time debugging the code.