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Re: 40x24 Resolution Question
- Subject: Re: 40x24 Resolution Question
- From: "Paul R. Santa-Maria" <paulrsm@buckeye-express.com>
- Date: Mon, 01 Apr 2002 12:51:28 GMT
- Newsgroups: comp.sys.apple2
- Organization: Giganews.Com - Premium News Outsourcing
- References: <P9Qp8.185824$2q2.15817951@bin4.nnrp.aus1.giganews.com> <1f9ywai.1aj12c9zj1lq8N%dempson@actrix.gen.nz> <IlSp8.177449$Gf.16513473@bin2.nnrp.aus1.giganews.com>
- Xref: archiver1.google.com comp.sys.apple2:18557
I do not understand the question "which addresses 280/7=40 and 192/8=24
are stored?". The text page is at $400-$7FF, allowing for the weird
mapping of address to lines and some 'screen holes'. For simplicity,
location $400 through $427 hold the data for the first screen line.
Write anything to those locations and they will show up on the first
line of the text screen.
The actual bitmaps of the characters are stored in a ROM in the video
circuitry. This ROM is not accessible to the 6502 and you cannot
read it from BASIC or assembly language. You can replace it
with a custom-programmed EPROM. One of my Apple IIe's has a double-
sized EPROM so I can switch between unenhanced and Mousetext.
Bryan Parkoff wrote:
>
> > The monochrome resolution of the Apple II video output is 280x192. In
> > text mode, each character is formed from a grid which is 7 pixels wide
> > and 8 pixels high. 280/7=40, and 192/8=24, so text mode is 40x24.
>
> It makes sense to me. I want to focus 280/7=40 and 192/8=24 that are
> text resolution. Where are they stored? You said ROM. I know that each
> character stores from $400 through $7FF, but which addresses 280/7=40 and
> 192/8=24 are stored? Curious....
>
> Bryan Parkoff
> BParkoff@satx.rr.com