Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!caen!math.lsa.umich.edu!math.lsa.umich.edu!hyc
From: hyc@math.lsa.umich.edu (Howard Chu)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Overscan
Keywords: Overscan
Message-ID: <1990Aug16.203308.12430@math.lsa.umich.edu>
Date: 16 Aug 90 20:33:08 GMT
References: <891@tharr.UUCP> <32562@sparkyfs.istc.sri.com>
Sender: usenet@math.lsa.umich.edu
Organization: University of Michigan Math Dept., Ann Arbor
Lines: 35

In article <32562@sparkyfs.istc.sri.com> arsen@sjc.itstd.sri.com.UUCP (Tom Arseneault) writes:
>In article <891@tharr.UUCP> guy@tharr.UUCP (Guy Gascoigne) writes:
>>I've seen various versions of the software for the Overscan mod. for an Atari
>>ST, but nowhere have I seen a description of what is required on the hardware
>>side. Does anyone know what needs to be done to a Mega 4 to get this to work.

>Just what is Overscan anyway??? I have a 1040STFM with a 16Mhz Jato
>board, 4mb memory, and both a color and mono monitor, what if anything
>will Overscan give me?

Overscan is a hardware mod that lets you use more pixels per screen.
With a multisync monitor, I have 736x480 mono resolution, 832x280 med rez,
and 416x280 low rez. With an SM124 monitor you can get 688x480. With an
SC1224 monitor you can get 720x280 med rez & 360x280 low rez.

The complete docs with illustrations are available at atari.archive.umich.edu
for anonymous ftp. The files are in ~ftp/atari/utilities. o_scan60.arc contains
a version that is said to work for color monitors in 60 hertz mode. (I was never
able to get it working, but there may have been strange interactions with my
Turbo-16 accelerator board.) The regular version plus all docs is in overscn3.arc.

I included another version of the binary with my port of fractint 12. This
version traps the Xbios SetScreen call, to set the correct screen dimensions
when switching between low & medium resolutions. The other versions don't trap
this call, resulting in garbled text displays after switching rez. My version
also sets 50 hertz video mode automatically for color displays. Note that if
you do get the o_scan60 version working for you, your max vertical resolution
will be 224. I can live with the 50 hz screen, so I get a little more flicker
but also 56 more pixel rows.

--
  -- Howard Chu @ University of Michigan
  one million data bits stored on a chip, one million bits per chip
	if one of those data bits happens to flip,
		one million data bits stored on the chip...