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Re: Blech! How can you stand 640x200??
- Subject: Re: Blech! How can you stand 640x200??
- From: mjmahon@aol.com (Michael J. Mahon)
- Date: 05 Jan 2001 05:24:54 GMT
- Newsgroups: comp.sys.apple2
- Organization: AOL http://www.aol.com
- References: <gzj16.31109$xW4.244515@news-server.bigpond.net.au>
- Xref: supernews.google.com comp.sys.apple2:4909
simon wrote:
>Television uses an interlaced display, where every second scanline is sent
>out in any particular frame. The Apple II sends out the same image for two
>consecutive frames, so that two adjacent scanlines actually will contain the
>same data. This is why the Apple's VBI (vertical blanking interrrupt) is
>only 25 Hz not 50 Hz.
Nope. the Apple VBI rate is 50/60 Hz.
For alternate field scan lines to display interlaced--as opposed to
superimposed--they must all start one-half line time later relative to
the vertical sync pulse. This timing is not
used by Apple video,
so all fields are superimposed, with half the lines and 50/60 Hz refresh rate.
(Frequency depends on PAL/NTSC, of course.)
-michael
Email: mjmahon@aol.com
Home page: http://members.aol.com/MJMahon/