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Progress on an S100 IBM-PC compatible BIOS

Just thought I would pass along something I spent the past few frustrating days on….


I have for a few weeks being writing a PC compatible BIOS  for our 8086 etc. card combinations so that you can boot any standard MS-DOS version from our cards setup. In particular the ZFDC S-100 Floppy disk controller, IDE controller and 8086 board. To recap see them here:- http://s100computers.com/My%20System%20Index%20Page.htm


I finally solved what the problem where I could read single sided MS-DOS V2.10 5" (360K) disk but not a Double sided same disk.  What had me baffled was the fact that I had no problem with PC CPM-86 DS disks.


Long story short.... The problem had to do with the way CPM & MS-DOS do disk sides. In CPM-86 I had 1-9 sectors on one side and for side B sectors were "called" 10-18.  i.e. there was no special set side command. In MS-DOS of course the side in in DH.


As is usually the case, very simple and obvious when you find it!


Now I will move on to higher DOS versions and 1.44 disks etc.   One thing this experience did do, is force me to add an extensive debug stream to a serial terminal . Displays all INT’s / registers etc. info etc. if requested.


I got back a nice e-mail from the SMT outfit www.proto-advantage.com (we both graduated from Mc. Master University there), so I am about to have them stick 3 of the VGA  SMT Cirrus Logic chips to their 0.1” adaptor boards.   After the 80286 I think a super VGA S-100 board will be our next board.   What I have not yet decided is if I should first do a wire-wrap PC ISA board here first or just go straight to S-100.