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Compaq Portable III / "Super CGA" graphics mode #111336 11/23/17 11:12 AM
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rfka01 Offline OP
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With mixmaster's interest, John Elliott's knowledge and the possible significance of having a generic "Super CGA" module that confirms to AT&T 6300 / Olivetti M24 standards, let's collect that information here smile

[Linked Image]

Other Computers that might benefit from emulating is graphics card/mode are the Toshiba T1000SE, the Toshiba T3100, some Nixdorf Laptops that TeamE's dumped for me last week, the DEC VAXmate, Brother Geobook and LW typewriters using Geoworks on a Vadem VG230 chip that supports the resolution, the Olivetti Quaderno and probably more. There's even a Borland BGI driver for it.

As of now, the Compaq Plasma driver for Windows 3.0/3.1 works if you install it on the Olivetti M24. If you use cga_m24 as graphics card on the Compaq Portable III, it tries to switch into graphics mode, but fails. The driver was omitted from the Windows for Workgroups 3.11 install disks, but can be re-introduced as outlined here. The GEM driver for the M24 is also reported to work on the Compaq portable III and 386.

[Linked Image]

crazyc had linked to the Olivetti M21/M24 theory of operation manual, and John Elliott has published the ports and interrupts involved as well as a comparison chart between different CGA supersets.

mixmaster has asked about switch settings, I'm linking to rather than embedding full size pictures from the inside of the back lid that has the switch settings for, among other things, the internal display.

https://imgur.com/84aCLkM
https://imgur.com/2YeuqLK
https://imgur.com/1yoiQqR

In addition to my original file you can download those pictures and some with previously hard to read chip labels here and on the FTP.

Interestingly enough, the Paradise VGA chip PVGA1A that I mentioned in the Commodore PC40-III thread retains the AT&T PC 6300 mode.


NCR DMV- DEC Rainbow- Siemens PCD- ITT 3030-Oly People- Acorn A5000- Olivetti M20
Re: Compaq Portable III / "Super CGA" graphics mode [Re: rfka01] #111337 11/23/17 11:42 AM
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The service manual mentions a "B000" page for Switch 7's "Monochrome Mode" that is not implemented anywhere in the M24's video hardware. I'm assuming that Compaq went a step further and implemented fully a MDA clone which lies separate of the internal video hardware, which can be toggled with the same switch that I mentioned earlier.

I'm assuming the external connection when in dual-mode is done via the "RGBI interface" as seen in the Personal Bulletin. I'm assuming "dual-mode monitor" on John's page refers to a standard multisync RGBI monitor, and "640x400 flat panel" means by the internal plasma panel. Not sure how the hardware detects if a "Compaq Color monitor" or "CGA 640x200" is present-- does it check for external cards?

Does bit 0 of 23C6h and reading 1BC6h have any effect when Switch 7 is set to "Boot Plasma Display in Monochrome Mode"? Also, what happens when you select "MDA" in bits 0-2 of 13C6h while the Portable III is in "Boot Plasma Display in Dual-Mode"? The page also mentions "EGA" for 13C6h as well-- but I'm not sure what that specifically means. I don't think the internal video hardware has EGA support-- does John mean by toggling the "Compaq Enhanced Color Graphics Board" as seen in here? ftp://ftp.oldskool.org/pub/drivers/Compaq/Portable%20III/c01138567.pdf

Re: Compaq Portable III / "Super CGA" graphics mode [Re: rfka01] #111338 11/23/17 11:46 AM
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rfka01 Offline OP
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Unfortunately my machine doesn't work, so I can't test this ... I hope there's an easy way to repair the power supply ...


NCR DMV- DEC Rainbow- Siemens PCD- ITT 3030-Oly People- Acorn A5000- Olivetti M20
Re: Compaq Portable III / "Super CGA" graphics mode [Re: rfka01] #111340 11/23/17 04:17 PM
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The Vadem VG230 is also used in the Pasogo so there's a partial emulation in there.

Re: Compaq Portable III / "Super CGA" graphics mode [Re: rfka01] #111341 11/23/17 04:37 PM
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Quote
that you can check your Portable motherboard to see if it has a 16257.00KHz XTAL


The mainboard itself has three crystals, 48.0000MHz, 1.8432 MHz, 24.0000 MHz, another that is marked "970HD - 14.318180 - 24.00000 M.P.C. 8725"

on the plasma controller board is one marked "970HD - 14.318180 - 16.098240 M.P.C. 8729"


NCR DMV- DEC Rainbow- Siemens PCD- ITT 3030-Oly People- Acorn A5000- Olivetti M20
Re: Compaq Portable III / "Super CGA" graphics mode [Re: rfka01] #111345 11/23/17 06:46 PM
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Well I'll be, 16.098240 MHz for a plasma display. Enough to handle a Hercules signal. I'm guessing that the signal for the monochrome mode comes from the 48MHz clock.

If the MDA mode is NOT a separate part of the video board completely using a completely different sync clock, it could be simply be an emulation running in Super CGA mode while forcing the IO port regardless of the jumper setting to 3A0-3BF and relocating the B800 page to B000 while also disabling 200 line text/graphics and 400 line graphics modes. After all, that's how VGA cards can do it.

Last edited by mixmaster; 11/23/17 07:06 PM.
Re: Compaq Portable III / "Super CGA" graphics mode [Re: rfka01] #111346 11/23/17 07:41 PM
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The Portable III's plasma display is supposed to have a 640x400 dot resolution in text mode, so I wouldn't expect it to use an MDA clock.

Re: Compaq Portable III / "Super CGA" graphics mode [Re: AJR] #111347 11/23/17 07:49 PM
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Originally Posted by AJR
The Portable III's plasma display is supposed to have a 640x400 dot resolution in text mode, so I wouldn't expect it to use an MDA clock.

Could be then that "monochrome mode" possibly does the latter, as mentioned above, where the text mode aspect of MDA is simulated instead of having the hardware having to conform to MDA completely on the fly.

Re: Compaq Portable III / "Super CGA" graphics mode [Re: AJR] #111348 11/23/17 08:23 PM
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Then again, if the MDA implementation was just a basic workaround in the Portable III's "Super CGA" hardware while it was still in "Dual-Mode", why would it not support an external monitor unlike in the "Dual-Mode" setting? To avoid people from accidentally plugging in and frying their MDA monitors?

The jumper settings imply that, well, external monitors might as well only work in the default "Dual-Mode" graphics position.

Re: Compaq Portable III / "Super CGA" graphics mode [Re: rfka01] #111349 11/23/17 08:53 PM
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It's worth mentioning that the "dual mode" CRT display on the Portable II was indeed capable of a 720x350 text mode as well as 640x200 graphics.

An interesting search result came up from a 1994 book called "SCO UNIX in a Nutshell." Apparently the "vidi" command in SCO UNIX could select between output to an internal monitor or to an external monitor on a "Compaq portable with plasma screen."

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