In post #111233
I presented the Compaq Portable III
and linked to a site that claims that its graphics card is compatible with the AT&T PC 6300/Olivetti M24
(640x400 monochrome, enhanced CGA, not-quite-EGA). Deriving from IBM 5170, the BIOS slots in nicely, and I gave it the m24_cga graphics card and the hdc hard disk controller which let me install DOS without a hitch.
A good test case for graphics compatibility is Windows 3.0 as it contains drivers for the Compaq 640x400 pixels Plasma screen that is used on the Portable III
and its successor, the Portable 386
After the text mode install, Windows tries to switch to graphics mode, and you can see it opening ... ahem ... Windows, but it fails to fully switch to graphics mode, leaving me with that colourful screen with lots of blinking characters.
If you launch Windows after one such botched installation attempt, you can see the boot screen in monochrome CGA for a fraction of a second, then the green text screen appears.
Time for a cross check: On the Olivetti M24
driver, the Windows installer correctly recognizes the AT&T/Olivetti graphics adapter, installs in text mode and then switches to graphics mode.
The coup de grace, however, is: If you install Windows 3.0 in the Olivetti M24
driver using the Compaq Portable Plasma setting
, Windows works just like with the proprietary Olivetti setting.
John Elliott gives some hints
on the peculiarities of the Portable III's video system - I'd love it if some minor tweak by a kind dev would allow the M24 adapter to be repurposed as a generic AT&T PC 6300 "super CGA" adapter - Team E's just dumped two early Nixdorf 286 Laptops that used that same chipset.
Under "Machine configuration - CGA monitor type" you can set different displays, e.g. an LCD - but the actual MAME display doesn't change. What additional steps are necessary to get the LCD screen simulation that is used in some drivers - and do we already have a red/amber plasma screen emulation?