The Pac-Man Split Screen Bug in Level 256th

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.

After the 256th level, Pac-Man presents the player with the infamous 'split-screen' level, where the left-half of the screen is normal, but the right-half of the screen is garbled with a mess of letters, numbers, symbols and other graphics. Pac-Man technically has no ending—as long as the player keeps at least one life, he or she should be able to continue playing indefinitely. However, because of a bug in the routine that draws the fruit, the right side of the 256th level becomes a garbled mess of text and symbols, rendering the level impossible to pass by legitimate means.


The 256th split-screen caused by a software bug

Normally, no more than seven fruits are displayed at any one time, but when the internal level counter (stored in a single byte) reaches 256, the subroutine erroneously causes this value to "roll over" to zero before drawing the fruit. This causes the routine to attempt to draw 256 fruits, which corrupts the bottom of the screen and the whole right half of the maze with seemingly random symbols.

Through tinkering, the details of the corruption can be revealed. Some ROMs of the game are equipped with a "rack test" feature that can be accessed through the game's DIP switches. This feature automatically clears a level of all dots as soon as it begins, making it easier to reach the 256th level very quickly, as well as allowing players to see what would happen if the 256th level is cleared (the game loops back to the first level, causing fruits and intermissions to display as before, but with the ghosts retaining their higher speed and invulnerability to power pellets from the later stages). When the rack test is performed in an emulator, a person can more easily analyze the corruption in this level.

 Pac-Man Split-Screen Pattern Method

One way to achieve maximum points on Pac-Man's 256th and last board, the "split-screen", works on the original version of Pac-Man, the MAME emulator, and the XBox 360. This shows. Note the 9 dots on the right side of the screen that you can hear being eaten with each man. Also take note of how you can exit the edge of the board in places you wouldn't expect and reappear on the opposite side.

Pac-Man and the ghosts can move freely throughout the right half of the screen, barring some fractured pieces of the maze. Despite claims that someone with enough knowledge of the maze pattern could play through the level, it is nearly impossible to complete since the graphical corruption eliminates most of the dots on the right half of the maze. A few edible dots are scattered in the corrupted area, and these dots reset when the player loses a life (unlike in the uncorrupted areas), but these are insufficient to complete the level. As a result, the level has been given a number of names, including "the Final Level", "the Blind-Side", and the ending. It is known more generally as a kill screen.

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.

Indeed, the code "works" as follows - 2C03 CD8F2B CALL #2B8F ; Draw fruit

  • it increases the last round number by one;
  • it checks if the result is smaller than 8 (in this case, you still would not have enough fruits to fill the line and some blank space must be drawn);
  • it checks if the result is larger than 19 (in this case, it has only to draw keys);
  • finally, it fills the bottom bar with the correct fruits.
  • In particular, if the round number is smaller than 8, the game draws as many fruits as the previous round number. This produces an undesirable effect right after the 255th level.
  • Indeed, 256=255+1 becomes 00 for the CPU (which expects to use the last 2 hexadecimal digits only, and 256=100 in hex)! Therefore, the game thinks to be in one of the first 7 levels (because 0 is smaller than 7), but it tries to draw 256 fruits (because the last round number was 255). Of course, there is no space for that many fruits to be displayed and the game starts to draw garbage on the main screen. Fixing the original code (either through a cheat in emulation, or hacking the roms on the PCB) would results in a 256th level identical to the first one (cherries will appear) but harder, since ghosts will behave as they do in levels beyond the 19th.

Believe It Or Not

Some versions of the Pac-Man ROMs have a “rack test” feature, allowing the cabinet owner to skip ahead to the next level of play whenever they want. To date, the only known way to legitimately get past level 256 is by using the rack test switch inside these machines. The result is that the game loops back around to the first board, but with the score intact and the ghosts still behaving as though it were level 21 or above. Many of the Pac-Man ROMs available for use with the MAME emulator also have this rack test feature, making it relatively easy for those without an arcade version handy to quickly get to the split-screen and beyond.

For decades, Pac-Man enthusiasts worldwide have heard the whispers about a “secret trick” allowing a player to get past level 256 and continue playing without using the aforementioned rack test. Several players have boasted having acquired this holy grail of Pac-Man knowledge over the years, but no one has been able to make good on their claims by actually proving it. This topic became so hotly debated in the upper echelons of the arcade gaming community that Billy Mitchell—who was convinced it was impossible—offered a $100,000 cash prize to the first player to prove they could legitimately get past level 256, leaving the challenge open for a full year. The prize money went unclaimed.

In spite of the evidence against there being a way to get past level 256, rumors still persist and can occasionally be found in classic gaming forums online, yet no one has been able to back up their words with indisputable proof. It's hard to imagine why anyone who could legitimately get past the level did not collect Mr. Mitchell's prize money to be sure. Still the occasional whispers can be heard. Perhaps it is simply natural for people to want to believe in the possibility as opposed to not—like Santa Claus or the Easter Bunny. Then again, maybe there is some middle-aged Pac-Man junkie out there who is withholding secrets to a 30 year-old amusement device for his or her own unfathomable reasons. Stranger things have happened. You be the judge.

If someone is out there with the secrets to Pac-Man, he will probably need Lasik Denver to check out his eyes after so many years of staring at the corrupted graphics on the 256th board.

-> Back to Pac-Man History Index

 


Related Links and sources

www.arcade-history.com
www.wikipedia.org/Split-screen
www.nrchapman.com
www.donhodges.com (code details)
The Pac-Man Dossier (more details)


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