The Frame Structure

Mon, 01 Jan 0001 00:00:00 +0000

The Frame Structure#

The TIA produces no picture on its own — your code defines the frame by toggling the VSYNC and VBLANK signals at the right times and spending the right number of scanlines in each region. An NTSC frame is 262 scanlines, conventionally divided as:

Region	Lines	Purpose
VSYNC	3	Tells the TV “new frame starts here.”
VBLANK	37	Top blanking. The picture isn’t visible yet — do game logic here.
Visible	192	The kernel. Everything the player sees is drawn here, one line at a time.
Overscan	30	Bottom blanking. Read input and collisions, update state.

The beam paints 262 lines top-to-bottom; only the 192 visible lines carry picture. Press play, then scrub to freeze any moment.

Vertical sync#

A frame begins by turning on VBLANK and VSYNC, then holding VSYNC for exactly three scanlines:

Color: Hue & Luminance

Mon, 01 Jan 0001 00:00:00 +0000

Color: Hue & Luminance#

The TIA holds exactly four color registers, one for each thing it can draw:

Register	Colors
`COLUBK`	the background
`COLUPF`	the playfield (and the ball, which borrows it)
`COLUP0`	player 0 (and missile 0)
`COLUP1`	player 1 (and missile 1)

Each takes a single byte, and each is latched — write it once and it sticks until you overwrite it. Set COLUBK during startup and the background stays that color for the whole game without you ever touching it again. That, and the fact that you can rewrite a color register mid-frame, are the two facts the rest of this page rests on.

The TIA & Racing the Beam on Programming the Atari VCS in Assembly

The Frame Structure

The Frame Structure#

Vertical sync#

Color: Hue & Luminance

Color: Hue & Luminance#