Jeff Blakeney wrote:
To: Michael J. Mahon On Tue, 6 Feb 2007 18:19:21 -0800, "Michael J. Mahon" <mjmahon@aol.com> wrote:This POKEs the first byte of the bitmap so that pages 0 and 1 are still "protected", but $200..$7FF is "free" (192 = $C0 = 1100 0000).Yeah, it just deprotects the memory from $400-$7FF, which is the text screen memory. Some DOS 3.3 programs load themselves into the text screen memory because they are only using the high res screen for display.
And to deter would-be deprotectors by causing any text output to clobber some (usually interesting) code. ;-) Many games that used text display loaded code into the text page at some point during their boot for this reason. -michael NadaNet networking for Apple II computers! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it's seriously underused."