X-Sender: daves@mail.interlog.com Date: Mon, 15 Apr 1996 22:43:06 -0400 From: daves@interlog.com (David Shadoff) Subject: Dually-compatible card Hi Folks... I had a (pretty good) thought as to how to make a card which functions in both the PC-E and the TG, WITHOUT NEEDING AN ADAPTER. The first segment is sacrificial and largely unused; key to the concept is the boot vector at offset $1FFE. If you put a pseudo-palindromic address in there, the bit-swizzle will point to a different (valid) location for the different machines. For example: $FFAA -> $FF55; $F780 -> $EF01; etc... At these addresses, one would program the MMR's to point to 'secondary' code segments (which would belong at $C000, for example). These code segments would then re-install the $E000 segment, depending on which machine. Then, you could have a 'bit-reverse' function for the graphic images (which are the most space-consumptive), so that they would not require duplication. Of course, you couldn't fit a BIG GAME into this; perhaps something simple like a 'Tennokoe Bank' or something... So, the segment map would look something like this (1 seg = 8KBytes): seg 1 -> sacrificial boot seg 2 -> $C000 (PCE) code seg 3 -> $C000 (TG) code seg 4 -> $E000 (PCE) (boot) code seg 5 -> $E000 (TG) (boot) code seg 6 -> graphic 1 seg 7 -> graphic 2 seg 8 -> graphic 3 If we did a 128K (1 Mbit) Tennokoe, then after this small but comfortable setup, we would still have 32 (2K) backup slots available. Whaddya think ? -- Dave