Sega Mega Drive / Genesis Large Tilemap Scrolling

An implementation using tilemap scrolling that allows playfields to be 8x larger. The window on the left is the plane explorer which demonstrates the technique.

As the camera moves around the level, in conjuction with scrolling, new columns and/or rows get drawn over old ones. The tiles are 16x16 pixels, so two rows or columns have to be updated at a time. This is done using a temporary buffer which gets populated with the tile data and is then updated using two DMA transfers. For a column, this is achieved by setting autoincrement to $80.

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