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. John,
I was at DRI when the decision was made about how to lay out the CP/M floppy disks. The difference between the way Microsoft sees the floppy and the way DIgital Research sees the floppy, have to do with how IBM sees Direct Access Storage Devices (DASD).
IBM reads all the data from all the heads of the device bore moving the heads to a new position.
This cuts down on the time necessary to format and read/write disk media because, when formatting for instance the heads only have to pass across the disk once, and writes both sides as doing so. As opposed to the way Microsoft sees the disk where the back is the second half of the drives.
By the way, you can tell a single sided CP/M disk from a double sided CP/M disk depending on the last byte of the first sector on the second side, whether it is a 0x01 or not. (ohhh a secret!!!)
Douglas
On Aug 21, 2011, at 10:40 AM, John Monahan wrote: 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.
---
//* * \\ (/(_•_)\) _/''*''\_ (/_)^(_\) Douglas Goodall douglas...@me.comhttp://www.goodall.com
|