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"This is the way the world ends
This is the way the world ends
This is the way the world ends
Not with a bang but with a whimper."
—T. S. Eliot
On
The Edge Of Forever
Pac-Man was always
meant to be a game with no ending. The developers at Namco
mistakenly assumed the game's increasing difficulty was sufficient
to prevent anyone from playing indefinitely. Of course, within a
few years of Pac-Man's release, players had discovered that every
level beyond the 21st was identical.
Patterns were
quickly created to exploit this fact and, for any player able to
get past the first 20 levels, the game now became a test of
endurance to see how many points you could rack up before losing
focus and making a mistake. High scores soared into the millions
and most players agreed the game simply went on forever.
Eventually, a few highly-skilled players were able to complete 255
consecutive levels of play (scoring over three million points and
taking several hours to accomplish) and found a surprise waiting
for them on level 256. It was a surprise no one knew about-not
even the developers at Namco.
The
256th level displays the left half of the maze
correctly, but the right half is a jumbled mess of randomly
colored letters, numbers, and symbols. Notice the bonus counter in
the lower-right of the screen is also malfunctioning.
The left
side of the maze plays normally, but the right side is a different
story. Although both the player and the ghosts can navigate
through the right half of the screen, the original maze walls no
longer apply.
Instead, Pac-Man must be guided through a confusing
series of open areas, tunnels, one-way intersections, lone walls,
and pass-throughs-all invisible to the player-while
four ghosts are in hot pursuit.
Why does this
broken level happen in the first place? The culprit is the routine
responsible for drawing the bonus symbols along the bottom edge of
the screen. Here's what happens: when level 256 is reached, the
internal level counter is incremented to 255 (the level counter
starts at zero - not one) and the routine for drawing the
bonus symbols is called.
The routine loads the current level
counter value (255) into a CPU register and increments that
register by one. Unfortunately, 255 is the largest number that can
fit in a single byte which is the size of the Z-80 CPU registers,
so when the value is incremented the overflow is discarded leaving
a zero in the register instead of the expected value of 256. This
zero value leads the routine to believe this is an early level
since its value is less than seven.
The routine starts drawing
bonus symbols using the confused register as a counter. At the end
of every drawing loop, the register is decreased by one and then
checked to see if it is zero (the signal for the routine to stop
drawing symbols). Since the register already has a zero in it to
start, the first decrement will roll the value back to 255. It
will keep decrementing the register and drawing symbols until the
register is reduced to zero again, causing the loop to run a total
of 256 times.
This means that memory locations outside the bounds
of the bonus symbol table are drawn to the screen at increasing
locations in video memory. This half-broken level was named the
"split screen" by players; developers refer to it as a
"kill screen".
Playing
The Level
There
are 114 dots on the left half of the screen, nine dots on the
right, and one bonus key, totaling 6,310 points. When all of the
dots have been cleared, nothing happens. The game does not
consider a level to be completed until 244 dots have been eaten,
so there is nothing left to do but sacrifice Pac-Man to a hungry
ghost.
Interestingly, every time a life is lost, the nine dots on
the right half of the screen get reset and can be eaten again,
resulting in an additional 90 points per extra man. In the
best-case scenario (five extra men), 6,760 points is the maximum
score possible, but only 168 dots can be harvested-not
enough to change levels-so we are stuck. There are no more
dots to gobble or energizers to eat.
There is no final victory
waiting for Pac-Man, only an empty half-maze full of ghosts. The
game has an ending after all-just not a very happy or
exciting one.
Four of the nine
dots on the right half of the screen are invisible, but can be
heard when eaten. The picture on the left shows all nine dot
locations. Dots 1, 5, 6, and 9 are invisible; the rest can be seen
but some are a different color than normal.
Anyone reaching
this level quickly realized: to safely map out the right side of
the screen something had to be done about the ghosts. After much
tinkering, it was discovered that a ghost would get "trapped"
on the right edge of the screen if he got too close to it.
Once
trapped, a ghost can only move up or down but never right or left
again. By leading ghosts near the edge of the screen, a skilled
player could eventually get the ghosts out of the way and
concentrate on exploring the right half of the maze and collecting
the dots.
There
are many methods for trapping the ghosts. One of the easiest ways
to trap the three important ghosts is shown in the picture to the
right. The yellow line shows Pac-Man's path from the start of the
level to a spot near the bottom-right.
The exact instructions are
as follows: begin by going right until you reach a blue letter
'N', then go down. Keep going down until you reach a blue letter
'F', then go right. Keep going right until you reach a yellow 'B',
then go down again. When executed properly, Pac-Man will hit an
invisible wall almost immediately after the last turn is made. Now
we wait.
The red ghost will get stuck first. The pink ghost
follows a few seconds later. The blue ghost will continue to move
freely for several moments until the next scatter mode occurs. At
that point, it will try to reach some location near the right edge
of the screen and get stuck with the pink and red ghost instead.
Now the orange ghost is the only one still on the loose
(bottom-right). Clyde is no real threat, however, since he runs to
his corner whenever Pac-Man gets close (see Chapter 4), making it
relatively easy to clean up all the dots. Be sure to take care
around the lower-left corner of the maze-the orange ghost
will have nowhere left to run to and will be much more aggressive.
Click on the
YouTube video below to watch this ghost-trapping method in action: