Read tiles from memory and display them on a framebuffer.
Tiles are stored at 0x8000 and are made up of 8*8 points, whereas each
points is described by two bits.
The whole window data is made up of
The whole window (32*32 tiles) is made up of references into the tile
space beginning at 0x9800. Each takes is 1 Byte.

The call instruction placed its return value on the wrong stack position