Grzyb wrote on 2022-02-08, 01:46:
Ltsyrek wrote on 2022-02-07, 21:04:
Could that:
Grzyb wrote:CGA/EGA/VGA + Hercules graphics is possible, under one condition: Hercules graphics software only using the first video page. […]
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CGA/EGA/VGA + Hercules graphics is possible, under one condition: Hercules graphics software only using the first video page.
CGA/EGA/VGA: B8000..BFFFF
Hercules text and first graphics page: B0000..B7FFF
Hercules second graphics page: B8000..BFFFF
There are some Hercules clones with a jumper to disable the second page.
be an issue? That this Winbond is using both video pages?
It's possible that some software has enabled the second page on Hercules, but this shouldn't corrupt the text mode.
I suspect the VGA card is guilty here - normally, VGA should map its memory at B0000..B7FFF only in modes 7 and F, but I'm not sure about VGAs newer than ISA...
Hi there! I think the same.
By the way, I've found a PDF of the original Hercules Monochrome Card.
https://www.minuszerodegrees.net/manuals.htm#Hercules
It seems that there was an utility called "HGC" that shipped with the original card.
The utility allowed activating both HALF and FULL mode. It also had a DIAG function.
- Maybe that's why Microsoft's MSHERC utility is useful to us, it contains the basic activation routines.
Because, after power on, the Hercules Monochrome behaves like this:
- Configuration switch is set to prevent setting graphics mode; Page 1 is masked and the Active Page bit can't be set yet
- IBM MDA emulation mode is activated (bit 1 set to 0: text mode; bit 1 set to 1: graphics mode)
- Active Page: Page 0 B0000-B7FFF (set via bit 7; if Page 1 is active: B8000-BFFFF, CGA's memory)
With these default settings, the Hercules Monochrome Card won't collide with anything (video related).
Because after power on, both Page 0 and Page 1 are actually mapped out of memory space.
The card is in textmode and merely occopies a tiny 4KB in the B0000-B0FFF range (just like IBM MDA).
That's why -in MDA compatible mode- it can be used in conjunction with a VGA card.
Debuggers used that possibility to have the Hercules clones work as primitve textgenerators to drive a status display.
It was cheaper than hooking up an serial terminal to AUX port, I suppose.
If we only had the original files of the GB101 diskette..:
HGC.EXE
FIXDIAG.EXE
HBASIC.EXE
HBASIC1 .EXE
PATTERN.BAS
FONT.COM
That would make testing things so much easier..
Edit: Here's the interesting bit about the utility from the manual..
"The Graphics Card's "Software Switch"
The Hercules Graphics Card model number GB 101 comes equipped with a
"software switch." The purpose of this switch is to allow you to manipulate the
Card with software to select one of three operating configurations.
Pay special attention to the information in this section on setting the "software switch".
This is something that needs to be done EACH TIME THE COM-
PUTER POWERS UP if you want to access either one 01' both "pages" of
screen buffer memory. If you forget to set the card into half 01' full
graphics mode, and you attempt to run any graphics software, your system will prob-
ably crash. If this happens, do a "soft boot" (CTRL-ALT-DEL) or power up again.
The DIAG configuration is the state which the card is automatically in after
power up. In this configuration, the graphics capabilities are masked, and
the Graphics Card emulates an IBM monochrome board for text only. No
graphics software may be run while in this mode.
The HALF configuration makes the first graphics page located at BOOOO-
B7FFF accessible to graphics software. The second graphics page located at
B8000-BFFFF is suppressed allowing the presence of other video cards
that their screen buffer does not occupy any portion of the first
provided graphics page. (This configuration allows the presence of an IBM Color Card
in the system at the same time as the Hercules Graphics Card.)
The FULL configuration makes the first and second graphics pages access-
ible to graphies software. "
Edit: I vaguely remember that the "CodeView" debugger used for Windows 3.1 development had the MDA feature..
Edit: Edited.
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