Perfect Pac-Man Game / Split Screen Explanation

I originally posted a few progress videos and pictures in the Non-Bemani Accomplishments thread on my forum and on Facebook but I have had a few comments about this and there is some confusion over just what happens on the last screen and why (in my video) I purposely sacrificed my lives on the last stage after mucking around the split screen

Okay, first things first, here is a video of me playing the last two stages (Videos for all the other unique stages on my youtube channel though I still have to upload a crap load of 9th key levels since they are all the same and it is so monotonous). The first in the video is the last playable stage, then you have the split-screen, and that is where the chaos starts:




About the Split Screen:



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”.


So how do you beat it?

You can't. The game will end on this stage. You can collect the dots on the left half of the screen, the one key that appears, and 9 dots hidden in the right side of the screen, of which only some are visible. They all make the familiar dot "gobble" sound when you pass over them, though. Here is where they are:



The amusing thing is that the 9 dots on the right side respawn every time you lose a life. Therefore, the best possible strategy is to make sure that regardless of when you finish off the left side of the screen, you must get the 9 hidden dots on the right side with each remaining man.

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Congrats on "beating" the "Kill Screen". Those are very fasinating to watch. By any chance have you seen The King of Kong: A Fist Full of Quarters?

Just curious, at what level does it become impossible to eat all 4 ghosts on 1 power pellet? And at what level do they stop becoming blue all together?

The ghosts stop becoming blue on level 17 and 19+. (The ghosts still turn blue on level 18, and levels 1-16.)

As long as the ghosts turn blue, it is always possible to eat all 4 ghosts on 1 power pellet by clustering them together, even when the time spent blue is only 1 second.

This link has tons of information about Pac-Man and is a very interesting read:
http://home.comcast.net/~jpittman2/pacman/pacmandossier.html

That's right. I actually think my videos of stages where the power pellets only last 1 second are far more interesting than when they don't have any effect other than altering the directions of the ghosts. I have them on my YouTube channel but I'll pick one out later when I get home and post that for reference. You have to cut it pretty close to get all 4 with every pellet sometimes.

Ah, here is a 1-second power pellet video:

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I just read the dossier and I'm wondering, have you ever attempted that ghost-phasing bug?

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wow that website was very insiteful and informative. Very fasinating. I wish there were more sites like this.