One of the many excellent features included in the ATARI Computers is
the automatic screen protection systems called the "ATTRACT
MODE". This system initiates a continuous rotation of colours on the
screen as protection against "burn through" which may occur when
a colour is displayed for too long without change. The computer monitors
the use of the keyboard and will automatically enter the "ATTRACT
MODE" if no keys have been depressed in the previous 9 minutes (9. 01
to be precise). As soon as the keyboard is used, the "ATTRACT
MODE" is disabled and the original screen colours return.
You may have found that some games, which use only paddles or
joysticks, enter into the "ATTRACT MODE" automatically after 9
minutes use. With a little bit of "peeking" and "pokeing"
you can discover what causes the "ATTRACT MODE" to begin and,
hopefully, how to temporarily disable it while you play your game.
The first thing you need to know is that the memory location which
governs whether the "ATTRACT MODE" will be activated or not is
location 77. By "peeking" into this location, you can see what
is happening during the 9 minutes before the system comes into operation.
The following short program should do the trick.
10 PRINT PEEK (77): GOTO 10
This program forms an endless loop which will repeatedly print the
contents of location 77. On running, you will see that the contents of
this location gradually increase in steps of 1 from 0. If you sat and
watched for long enough, you would eventually see something strange happen
to the sequence of numbers. To speed things up a little you can add an
extra line to the program and run it again to watch the results.
5 POKE 77, 125
This line inserts a value of 125 into location 77 and on running you
will see that the values displayed start at 125 and not 0 as previously.
This value will gradually increase until 127 is displayed. The next number
shown will be 254 and at this point the "ATTRACT MODE" will be
activated.
You can see from this that if location 77 contains a value of 127 or
less, then the "ATTRACT MODE" will remain inoperative. The ideal
situation from a game - playing point of view would be to place a 0 in
this location as of ten as possible or at least every 9 minutes. This can
be done by including an instruction POKE 77, 0 in a frequently used part
of the program (e.g a "movement" or "fire" routine).
This will ensure that the attract mode remains inoperative during the
course of the game.
As a matter of interest, this is precisely what happens when a key is
depressed. If you run the program again and then press a key you will see
that the value shown will immediately change to 0 and gradually increase
as before. Any subsequent pressing of keys will have the same effect.
If you want to use the "ATTRACT MODE" during one of your own
programs this is easily done by issuing the instruction POKE 77,254. The
system can then be disabled at the appropriate point by a POKE 77, 0
instruction.
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