Minor Pac-Man fault

big10p

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This is on an original Ms Pac-Man board that's been converted to Pac-Man.

Game plays fine, but on the first intermission screen, there's a row of yellow dashes at the top of the screen. They don't appear until giant Pac-Man chases the ghost off to the right, and the yellow dashes scroll to the right.

Any pointers to possible cause much appreciated.

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Update: I now have 3 Pac boards and they all do this, so I guess it's normal. 🤷‍♂️
Never noticed that on my Pacman, is your monitor adjusted so the game fills the screen properly? Also the position could be off
 
More than likely a horizontal width coil adjustment thing. Probably just need to bump the horizontal width up so the dashes are hidden off screen. Likely just RAM garbage which is stored on the edge of the screen which is common with these games.
 
Never noticed that on my Pacman, is your monitor adjusted so the game fills the screen properly? Also the position could be off
It's adjusted to pretty much max height. Pretty sure if I adjust it off screen, I'll loose the top of the score line. I'll give it a try, though.
 
More than likely a horizontal width coil adjustment thing. Probably just need to bump the horizontal width up so the dashes are hidden off screen. Likely just RAM garbage which is stored on the edge of the screen which is common with these games.
Be interesting to hear if anyone else gets these lines when adjusting their monitor to reduce height. I've tried it in two cabs. Don't think I've ever seen it in emulators like MAME, either.
 
I haven't really investigated this, but its most likely a bug in the /HBLANK logic that essentially shifts the screen 1 pixel.

The lines you see are the sprites being drawn to the line RAMs, when the screen is still supposed to be blanked. Only the big pacman sprites use the bottom row of pixels, so only they'll show up there.

The either needed one more or one less 6mhz delay in /HBLANK going through 4B to 3B/4C.
 
I haven't really investigated this, but its most likely a bug in the /HBLANK logic that essentially shifts the screen 1 pixel.

The lines you see are the sprites being drawn to the line RAMs, when the screen is still supposed to be blanked. Only the big pacman sprites use the bottom row of pixels, so only they'll show up there.

The either needed one more or one less 6mhz delay in /HBLANK going through 4B to 3B/4C.
Wow, sounds like you know your stuff. Thanks for the info.
 
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