Can't do minecraft Xbox 360 edition split screen with hd?

I got an hdmi cable and second controller for my Xbox 360 slim recently. I plugged in the cable to my Xbox and my tv. My screen shows up on channel hdmi and it's Definitely hd. With both controllers signed in on hdmi channel yet it doesn't show that extra screen to connect my other controllers or tell me to press start in-game. My tv is an HDTV so what's wrong?