For more information view the Sega-16 thread below.
Quote from Chilly Willy:
"This is a thread for demos of the "new" video mode using DMA to generate a direct color RGB display on the MD. For details on how it works, you might read the long thread over at SpritesMind. In the meantime, devs like yours truely will post some examples here. This first example is a simple raycast engine like used in Wolf3D. It draws a simple level using a few W3D textures. You move around using the d-pad, and A and C strafe left/right. That's all this does at the moment. ... And now with collision detection! No more walking through walls, but you do slide along them nicely when at an angle. I also made sure every area in the map can be reached... which is good since you can't reach them by walking through the walls anymore. "
http://www.sega-16.com/forum/showthread.php?23426-Direct-Color-DMA-video...