Tile based movement on Actionscript 2.0 (adobe flash cs6)

So I have got this problem where I do not know how to possible code tile based movement in 4 directions (NSWE) for action script 2.0.

I have this code but it is dynamic movement, which makes the char move in all 8 directions (NW,NE,SW,SE N,S,W,E). The goal is to limit the movements to tile based and in only 4 directions (NSEW)

 onClipEvent(enterFrame)
{
    speed=5;
    if(Key.isDown(Key.RIGHT))
    {
        this.gotoAndStop(4);
        this._x+=speed;
    }
    if(Key.isDown(Key.LEFT))
    {
        this.gotoAndStop(3);
        this._x-=speed;
    }
    if(Key.isDown(Key.UP))
    {
        this.gotoAndStop(1);
        this._y-=speed;
    }
    if(Key.isDown(Key.DOWN))
    {
        this.gotoAndStop(2);
        this._y+=speed;
    }
}

The most simple and straightforward way is to move that thing along X-axis OR along Y-axis, only one at a time, not both.

onClipEvent(enterFrame)
{
    speed = 5;

    dx = 0;
    dy = 0;

    // Figure out the complete picture of keyboard input.

    if (Key.isDown(Key.RIGHT))
    {
        dx += speed;
    }

    if (Key.isDown(Key.LEFT))
    {
        dx -= speed;
    }

    if (Key.isDown(Key.UP))
    {
        dy -= speed;
    }

    if (Key.isDown(Key.DOWN))
    {
        dy += speed;
    }

    if (dx != 0)
    {
        // Move along X-axis if LEFT or RIGHT pressed.
        // Ignore if it is none or both of them.

        this._x += dx;

        if (dx > 0)
        {
            this.gotoAndStop(4);
        }
        else
        {
            this.gotoAndStop(3);
        }
    }
    else if (dy != 0)
    {
        // Ignore if X-axis motion is already applied.
        // Move along Y-axis if UP or DOWN pressed.
        // Ignore if it is none or both of them.

        this._y += dy;

        if (dy > 0)
        {
            this.gotoAndStop(2);
        }
        else
        {
            this.gotoAndStop(1);
        }
    }
}