Q. What are the basic video modes ?

1. Bitmap mode:

• Planar: 1-8 bitplanes (1-256 colours from indexed palette)
• "Chunky": 1 byte = 1 pixel (256 colours from indexed palette)

2. Tilemap mode with optional dual playfield

All modes have hardware scroll. (Sprites are independant and work across all modes.)

Q. What is the tilemap video mode ?

A. In this mode you have tilemaps and tile definitions. Each tile is 16x16 pixels and fixed at 256 colours (pixel data is arranged in "chunky" fashion). The tilemap dictates what tile image appears where. Each playfield can be smoothly scrolled independantly in horizontal and vertical directions using hardware registers.

Q. What is the physical memory organization, for different video modes?

A. One 128KB physical memory chip stores only sprites definitions. Another 512KB chip stores the tile map and tiles, bitmap data. The two chips have their own busses allowing fast throughput.

Q. What is the blitter?

A. The blitter is used to perform fast copy operations within video memory. The speed of a copy operation is about 100KB per frame @ 50Hz.
(1 byte every 2 cycles) The blitter can copy rectangular areas within wider frames by using modulo offsets. It can also skip the writing of zero value bytes if required (for simple transparancy / masking)

Q. Is the blitter available in both bitmap and tilemap video modes ?

A. Yes.

Q. How many sprites are available.

A. 55 per line. There are actually 127 sprite registers available, if there is time the sprites from the upper registers are displayed (this can be thought of as a kind of free hardware multiplexing)

Q. How big are the sprites?

A. 16 pixels wide, height up to 240 pixels. All sprites are 256 colours (chunky style data arrangement).