Differences

This shows you the differences between two versions of the page.

--- graphics:memory [2023/08/22 23:53] – clyde
+++ graphics:memory [2023/12/18 04:10] (current) – [Sprite RAM] clyde
@@ Line 17: / Line 17: @@
 The blitter may read anywhere within a 256x256 page as a contiguous region. When accessed by the CPU however, only one quadrant of the currently selected sprite page is mapped in at a time.
-The quadrant selected for CPU access is determined by the state of the blitter's sprite cursor. Whichever quadrant the sprite cursor was in at the end of the last blitter operation will be the quadrant accessed by the CPU in direct mode.
+The values of GX and GY last used by the Blitter will also influence which part of Sprite RAM the CPU can access in addition to the Banking Register. The video section of the memory map is only big enough for a 128x128 region. So the quadrant of Sprite RAM available to the CPU is determined by the most significant bit in the Sprite RAM coordinate counters. Typically these would be set before loading sprites by running a single-pixel blit operation copying from the target quadrant to an off-screen portion of the framebuffer.