At 09:33 PM 4/27/05 -0500, you wrote: You're not, I have one and I strongly suspect Tony does too. Joe

[Techrefs] I do. It's a very complete manual, covering the mainboard, PSU, floppy controller, modem, parallel port sidecar, CGA monitor, printers, etc). There are 3 scehamtics 'missing' IMHO, though -- the floppy drive (which is, however, in the normal O&A techref), the PSU brick (which is just a transformer, I know, I built one...) and the keyboard. The IR receiver is there, as is a description of the keyboard protocol. I've never really trusted diagnostic programs. Trying to test a non-working device using a non-working device (itself!) doesn't seem to be very reliable. OK, it'll find things like a dead serial port buffer chip, but that's easy to find anyway.... I have one, with the parallel port sidecar, 64K memory expansion card and internal floppy drive. What do you need to know? If it's not too much, I can look it up in my techrefs... -tony -tony

Tony Duell wrote: Well, nothing that probably already hasn't been stated before -- I know the specifications of the Motorola 6845 and how it works, and I know that the tech ref documents each CRTC register, etc... what I'm looking for is stuff that probably isn't in the tech ref, like "what are the invalid settings for each register", etc as implemented on the CGA. I say this because, to prove a point to a few of my colleages, I'm writing a program that does unholy things with CGA that it were probably never intended by the hardware designers. In addition to writing code for "approved" uses like 160x200x16 (composite) and the "third" red-cyan-white palette (disable color burst), I'm trying to see just how much it can do. I've got working code for 160x100x16 (tweaked text), 60Hz full-screen horizontal scrolling via the address CRTC registers, all 16 colors onscreen in all graphics modes, etc. but I recall some rumors about 256-byte-wide modes, undoing the display memory interleaving, and some other stuff that I can't confirm/deny. In other words, stuff that the MC6845 can do but the hardware implementation of CGA can't (or can if doing something "undocumented"!). -- Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/ Want to help an ambitious games project? http://www.mobygames.com/ Or check out some trippy MindCandy at http://www.mindcandydvd.com/

Tony Duell wrote: Considering that the 160x200 composite color mode was actually documented, that stinks! Okay, looking at MC6845 specs right now... That's their problem :-) I have a true blue CGA card, so that's what I'm going to hammer on. Thanks for checking for me! -- Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/ Want to help an ambitious games project? http://www.mobygames.com/ Or check out some trippy MindCandy at http://www.mindcandydvd.com/

On Thu, 2005-04-28 at 19:28 -0700, Vintage Computer Festival wrote: You have multiple brains? :-)

Tony Duell wrote: Was there every a CGA techref? (Most likely not since it's touched on in the PC tech ref, but just curious) -- Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/ Want to help an ambitious games project? http://www.mobygames.com/ Or check out some trippy MindCandy at http://www.mindcandydvd.com/

Tony Duell wrote: ...which I don't have :) Oh well, hopefully there's electronic copy somewhere. I don't have that either, but I've disassembled my own BIOS and found that it is nearly useless to me -- for example, there are instructions that take longer to execute out of RAM (4 cycles per byte opcode) than ROM (2 cycles) -- so it's not so much of "let's optimize what the BIOS code can do" but rather "I need to come up with a completely different way of doing this". Which is what I expect a lot of people were doing in the '60s and '70s ;-) -- Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/ Want to help an ambitious games project? http://www.mobygames.com/ Or check out some trippy MindCandy at http://www.mindcandydvd.com/

Tony Duell wrote: Yes, but not sure what point you're making. Memory accesses to ROM were faster than RAM, so the ROM could get away with this code to put a character+attribute onscreen without "snow" during horizontal retrace: MOV AX,BX STOSW ...but doing so from RAM wouldn't work because the MOV AX,BX is a 2-byte opcode that took 8 cycles to fetch, so it wouldn't be fast enough and you'd see snow. This drove me quite insane until I figured it out; I modified my own code to use a 1-byte opcode: XCHG AX,BX STOSW ...since I didn't need to preserve either AX or BX after the STOSW. This did the trick. I can just imagine you doing this, LOL :-) The BIOS CGA code for putting a pixel element on the screen is particularly inefficient, for example, which is why it is so damn slow. -- Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/ Want to help an ambitious games project? http://www.mobygames.com/ Or check out some trippy MindCandy at http://www.mindcandydvd.com/

On Wed, 27 Apr 2005, Scott Stevens wrote: I know, I'm, increasingly saving more of this stuff, surprisingly. When you happen to actually need it (rare, but it comes up) you realize it's not so much dead weight after all :) -- Sellam Ismail Vintage Computer Festival ------------------------------------------------------------------------------ International Man of Intrigue and Danger http://www.vintage.org [ Old computing resources for business || Buy/Sell/Trade Vintage Computers ] [ and academia at www.VintageTech.com || at http://marketplace.vintage.org ]

I suspect finding a PC motherboard -- with a cassette port -- is even harder. Why would you want one? Well, the Microprofessor MP1/88 is an 8080-based machine with an IBM PC compattible cassette port (and no other built-in storage). In theory you can cross-develop code on an PC, save it to cassette, and load it in to the Microprofessor. -tony

On Thu, 28 Apr 2005 00:02:48 +0100 (BST) ard at p850ug1.demon.co.uk (Tony Duell) wrote: I can remember when the 8088 clone motherboards all still came with a full schematic. I even still have some of those manuals. It used to be possible to use the schematic from just about ANY clone motherboard to troubleshoot and repair any other, because the 'cloning' was that exact, right down to the 74xx chip level, and often IC part number. It made troubleshooting those motherboards down to the component level pretty easy. They really WERE clones.