Ringer

• 来源：Ringer - HDLBits

Problem Statement

Suppose you are designing a circuit to control a cellphone's ringer and vibration motor. Whenever the phone needs to ring from an incoming call (input **ring**), your circuit must either turn on the ringer (output **ringer** = 1) or the motor (output **motor** = 1), but not both. If the phone is in vibrate mode (input **vibrate_mode** = 1), turn on the motor. Otherwise, turn on the ringer.

Try to use only assign statements, to see whether you can translate a problem description into a collection of logic gates.

Design hint: When designing circuits, one often has to think of the problem "backwards", starting from the outputs then working backwards towards the inputs. This is often the opposite of how one would think about a (sequential, imperative) programming problem, where one would look at the inputs first then decide on an action (or output). For sequential programs, one would often think "If (inputs are ___ ) then (output should be ___ )". On the other hand, hardware designers often think "The (output should be ___ ) when (inputs are ___ )".

The above problem description is written in an imperative form suitable for software programming (if ring then do this), so you must convert it to a more declarative form suitable for hardware implementation (_assign ringer = ____). Being able to think in, and translate between, both styles is one of the most important skills needed for hardware design.

Tip

For this particular problem, one should be thinking "The motor is on when ___", rather than "If (vibrate mode) then ___".

Official Solution

module top_module(
    input ring, 
    input vibrate_mode,
    output ringer,
    output motor
);

    // When should ringer be on? When (phone is ringing) and (phone is not in vibrate mode)
    assign ringer = ring & ~vibrate_mode;

    // When should motor be on? When (phone is ringing) and (phone is in vibrate mode)
    assign motor = ring & vibrate_mode;

endmodule

My Solution

module top_module (
    input ring,
    input vibrate_mode,
    output ringer,       // Make sound
    output motor         // Vibrate
);
    always@(*)begin
        if(ring)begin
            if(vibrate_mode)begin
                motor <= 1'b1;
                ringer <= 1'b0;
            end
            else begin
                motor <= 1'b0;
                ringer <= 1'b1;
            end
        end
        else begin
            motor <= 1'b0;
            ringer <= 1'b0;
        end
    end

endmodule