|Attract mode timer and flag
Attract mode rotates colors on your screen at low luminance levels when the computer is on but no keyboard input is read for a long time (seven to nine minutes). This helps to save your TV screen from "burn-out" damage suffered from being left on and not used. It is set to zero by IRQ whenever a key is pressed, otherwise incremented every four seconds by VBLANK (see locations 18 - 20; $12 - $14). When the value in ATRACT reaches 127 ($7F), it is then set to 254 ($FE) until attract mode is terminated. This sets the flag to reduce the luminance and rotate the colors when the Atari is sitting idle. POKE with 128 ($80) to see this effect immediately: it normally takes seven to nine minutes to enable the attract mode. The OS cannot "attract" color generated by DLI's, although your DLI routine can, at a loss of time. Joysticks alone will not reset location 77 to zero. You will have to add a POKE 77,0 to your program periodically or frequently call in a subroutine to prevent the Atari from entering attract mode if you are not using any keyboard input.