Great Hierophant
February 28th, 2008, 09:09 PM
I have a pair of true Hercules Graphics Cards. These cards support both the MDA text mode and unique Graphics Mode. These cards come with 64KB of RAM and use B000-BFFF. However, there is a setting on these cards to disable 32KB of RAM and restrict the card to B000-B7FF. This is called Half-Graphics Mode and is designed to avoid conflicts with a CGA card in the same system. Unfortunately, there is no jumper I can see on the early Hercules cards to put the card into Half-Graphics Mode. I have a disk of utilities from Hercules that I cannot access as I lack the energy to test a 5.25" drive. I assume the disk had a utility to do this.
But even if you cannot switch the early Hercules cards, is this going to be a problem if you use it with another graphics card, and how?
If you have a CGA/EGA or VGA card and a Hercules card in the same system, it will not matter one whit in text mode. Hercules text mode starts at B000, the others start at B800 unless they are emulating an MDA. The system or DOS will determine which text mode to begin in.
Graphics mode is another issue. Most programs do not try to "read" graphics RAM, they simply write to it. EGA and VGA use A000-AFFF, which does not conflict with the Hercules. CGA does conflict. If a program is set to use Hercules graphics, then you cannot use another program using CGA graphics or MDA/CGA/EGA/VGA text at the same time. The screen connected to the non-Hercules card would show garbage because its display RAM is being filled with the same graphics data being sent to the Hercules. The simple solution would be to turn off the monitor not connected to the Hercules card until you had no further need of Hercules graphics, and vice versa.
But even if you cannot switch the early Hercules cards, is this going to be a problem if you use it with another graphics card, and how?
If you have a CGA/EGA or VGA card and a Hercules card in the same system, it will not matter one whit in text mode. Hercules text mode starts at B000, the others start at B800 unless they are emulating an MDA. The system or DOS will determine which text mode to begin in.
Graphics mode is another issue. Most programs do not try to "read" graphics RAM, they simply write to it. EGA and VGA use A000-AFFF, which does not conflict with the Hercules. CGA does conflict. If a program is set to use Hercules graphics, then you cannot use another program using CGA graphics or MDA/CGA/EGA/VGA text at the same time. The screen connected to the non-Hercules card would show garbage because its display RAM is being filled with the same graphics data being sent to the Hercules. The simple solution would be to turn off the monitor not connected to the Hercules card until you had no further need of Hercules graphics, and vice versa.