TECH: Pacman video issue

Archived from groups: rec.games.video.arcade.collecting (More info?)

probably been covered a million times, but I'm just not getting it..

OK.. The game seems to run fine: the monsters & pac (the sprites) appear
normally, and follow the maze, but the maze is not there... Clearly the CPU
sees and properly reads and writes to the scratchpad RAM, but the screen
data is not selecting the proper character in the graphics ROM.

Could someone enlighten me on the path the data takes from video RAM to the
character ROMs? I've scoped all the lines, and I can find no bus
contention.

HELP!

Thanks,

Chris
4 answers Last reply
More about tech pacman video issue
  1. Archived from groups: rec.games.video.arcade.collecting (More info?)

    one of the colour proms???
    "Chris Brooks" <armis2000.no spam@earthlink.net> wrote in message
    news:2J5le.8023$uR4.4833@newsread2.news.atl.earthlink.net...
    > I should add that the screen is full of the dots that pac normally eats,
    but
    > they do not dissappear in the attract mode, and are at every position on
    the
    > screen (except the score area and credit area - those are some other
    garbage
    > character)
    >
    >
    >
  2. Archived from groups: rec.games.video.arcade.collecting (More info?)

    OK... Progress...

    Something MAME is useful for is playing with memory locations :)

    Looks like the color data is being used for the character data. So when
    pink lettering is written, first the characters are written to VRAM, then
    the color information is written to color RAM. Since in attract mode, there
    is red for inky, pink for pinky, etc, and pink is the same value color for
    that line of characters: garbage of all the same character is seen on that
    line!

    Now to find what ram is what, and what the heck is going on with the
    addressing :)

    "VaxX" <geoff_gunn@hotmail.com> wrote in message
    news:4295ca9b$0$253$61c65585@uq-127creek-reader-03.brisbane.pipenetworks.com.au...
    > one of the colour proms???
    > "Chris Brooks" <armis2000.no spam@earthlink.net> wrote in message
    > news:2J5le.8023$uR4.4833@newsread2.news.atl.earthlink.net...
    >> I should add that the screen is full of the dots that pac normally eats,
    > but
    >> they do not dissappear in the attract mode, and are at every position on
    > the
    >> screen (except the score area and credit area - those are some other
    > garbage
    >> character)
    >>
    >>
    >>
    >
    >
  3. Archived from groups: rec.games.video.arcade.collecting (More info?)

    try the ram at 2a - 2d. Swap locations and see if it changes.


    "Chris Brooks" <armis2000.no spam@earthlink.net> wrote in message
    news:Kqsle.11121$w21.2921@newsread3.news.atl.earthlink.net...
    > OK... Progress...
    >
    > Something MAME is useful for is playing with memory locations :)
    >
    > Looks like the color data is being used for the character data. So when
    > pink lettering is written, first the characters are written to VRAM, then
    > the color information is written to color RAM. Since in attract mode,
    there
    > is red for inky, pink for pinky, etc, and pink is the same value color for
    > that line of characters: garbage of all the same character is seen on that
    > line!
    >
    > Now to find what ram is what, and what the heck is going on with the
    > addressing :)
    >
    > "VaxX" <geoff_gunn@hotmail.com> wrote in message
    >
    news:4295ca9b$0$253$61c65585@uq-127creek-reader-03.brisbane.pipenetworks.com
    ..au...
    > > one of the colour proms???
    > > "Chris Brooks" <armis2000.no spam@earthlink.net> wrote in message
    > > news:2J5le.8023$uR4.4833@newsread2.news.atl.earthlink.net...
    > >> I should add that the screen is full of the dots that pac normally
    eats,
    > > but
    > >> they do not dissappear in the attract mode, and are at every position
    on
    > > the
    > >> screen (except the score area and credit area - those are some other
    > > garbage
    > >> character)
    > >>
    > >>
    > >>
    > >
    > >
    >
    >
  4. Archived from groups: rec.games.video.arcade.collecting (More info?)

    I beleive those RAM are for the sprites (ghosts & pac) - the sprites render
    just fine, just not the maze.

    Chris
    "VaxX" <geoff_gunn@hotmail.com> wrote in message
    news:42970188$0$255$61c65585@uq-127creek-reader-03.brisbane.pipenetworks.com.au...
    > try the ram at 2a - 2d. Swap locations and see if it changes.
    >
    >
    > "Chris Brooks" <armis2000.no spam@earthlink.net> wrote in message
    > news:Kqsle.11121$w21.2921@newsread3.news.atl.earthlink.net...
    >> OK... Progress...
    >>
    >> Something MAME is useful for is playing with memory locations :)
    >>
    >> Looks like the color data is being used for the character data. So when
    >> pink lettering is written, first the characters are written to VRAM, then
    >> the color information is written to color RAM. Since in attract mode,
    > there
    >> is red for inky, pink for pinky, etc, and pink is the same value color
    >> for
    >> that line of characters: garbage of all the same character is seen on
    >> that
    >> line!
    >>
    >> Now to find what ram is what, and what the heck is going on with the
    >> addressing :)
    >>
    >> "VaxX" <geoff_gunn@hotmail.com> wrote in message
    >>
    > news:4295ca9b$0$253$61c65585@uq-127creek-reader-03.brisbane.pipenetworks.com
    > .au...
    >> > one of the colour proms???
    >> > "Chris Brooks" <armis2000.no spam@earthlink.net> wrote in message
    >> > news:2J5le.8023$uR4.4833@newsread2.news.atl.earthlink.net...
    >> >> I should add that the screen is full of the dots that pac normally
    > eats,
    >> > but
    >> >> they do not dissappear in the attract mode, and are at every position
    > on
    >> > the
    >> >> screen (except the score area and credit area - those are some other
    >> > garbage
    >> >> character)
    >> >>
    >> >>
    >> >>
    >> >
    >> >
    >>
    >>
    >
    >
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