keyDown(key) {
        if (key === 'Backspace') this.delete();
        if (this.selectedIndex === undefined) return;
        key = key.toLowerCase();
        if (!~'1234567890abcdef'.indexOf(key)) return;

        this.data[this.selectedIndex] = (this.data[this.selectedIndex] * 16 + parseInt(key, 16)) % 256;
    }
@memberof Rom
to take input in rom
@return {number}