EGA rows/cols? 
Author Message
 EGA rows/cols?

I was thinking about the possibilities (because I enjoy playing with
this) of making an EGA simulator for the old (ancient) Hercules video card.

Now I'm not a super programmer, and was wondering if this was at all
possible, or even has been done before. I know there are a number of CGA
simulators for the Hercules Card, but I haven't seen any EGA.

Help?

--
                .-~~~~~~~~~-._       _.-~~~~~~~~~-.
            __.'  "Wanderer"  ~.   .~ wandered: on `.__
          .'//   names me the   \./ the Earth's back \\`.
        .'//  World; widely have |  I have travelled   \\`.
      .'// .-~"""""""~~~~-._   I | far._,-~~~~"""""""~-. \\`.

  .'//______.============-..   \ | /   ..-============.______\\`.
.'______________________________\|/______________________________`.



Wed, 18 Jun 1902 08:00:00 GMT  
 EGA rows/cols?

Quote:

> I was thinking about the possibilities (because I enjoy playing with
> this) of making an EGA simulator for the old (ancient) Hercules video card.

> Now I'm not a super programmer, and was wondering if this was at all
> possible, or even has been done before. I know there are a number of CGA
> simulators for the Hercules Card, but I haven't seen any EGA.

Take a look at the modes involved:

Herc    720x348x2       Hercules
4,5     320x200x4       CGA,EGA
6       640x200x2       CGA,EGA
0D      320x200x16      EGA
0E      640x200x16      EGA
0F      640x350x2       EGA
10      640x350x16      EGA

The CGA emulators do modes 4,5 & 6. Mode 6 is easy. Modes 4 & 5 can be
done by using "shading" (patterns) to emulate the colors.

Mode 0F is "easy", but it's only uised when you have a mono monitor
attached to an EGA card.

Lets look at mode 0Dh. 320x200 is 64,000 pixels. 720x348 is 250,560
pixels. So on the average, you have 3.9 Herc pixels per mode 0Dh pixel.
No way are you going to get 16 shades out of that! Hell, you can barely
get 16 *patterns*.

Mode 0Eh has 120,000 pixels. So that's only 1.9 herc pixels per mode
0Eh pixel. No way are you getting 16 colors out of that.

Mode 10 is *definitely* out of the question. There's only 1.1 Herc
pixels per mode 10 pixel.

So, the answer is no, it isn't possible.

Leonard Erickson (aka Shadow)




Wed, 18 Jun 1902 08:00:00 GMT  
 EGA rows/cols?

Quote:

>I was thinking about the possibilities (because I enjoy playing with
>this) of making an EGA simulator for the old (ancient) Hercules video card.
>Now I'm not a super programmer, and was wondering if this was at all
>possible, or even has been done before. I know there are a number of CGA
>simulators for the Hercules Card, but I haven't seen any EGA.
>Help?

I'm not really sure how feasible this would be.  Each level of video is far
more complex than the last -- HGC/mono, CGA, EGA, VGA, SVGA.  Of those,
there are two groups that are reasonably close:  HGC-CGA and VGA-SVGA.  
There's a bit of connection between EGA and VGA in general design, but
there's enough difference (enhanced VGA BIOS has more calls, most EGA
registers are write-only, 8 bit versus 16) that I wouldn't group them that
closely, IMHO.

Trying to produce an EGA emulator for monochrome would be extremely
difficult due to the differences in function and architecture.  Even writing
an EGA emulator for CGA would be a feat in itself.  I was considering
writing a VGA emulator for EGA when I decided that even between those that
have a similar BIOS interface, it was far too ugly an undertaking to be
worthwhile.

If you're still convinced this is something you want to do, keep a couple
things in mind:  First, it's never going to be much more than a novelty
item, no matter how well it works.  Second, the interest level will probably
be very small.  And third, read up extensively on how each of the hardware
implementations works.  A good starting point might be _Programmer's Guide
to the EGA and VGA cards_ by Richard F. Ferraro.  This mostly covers EGA and
VGA, although there's some information about the earlier video cards, and
some SVGA chipsets.

Quote:
>--
>                .-~~~~~~~~~-._       _.-~~~~~~~~~-.
>            __.'  "Wanderer"  ~.   .~ wandered: on `.__
>          .'//   names me the   \./ the Earth's back \\`.
>        .'//  World; widely have |  I have travelled   \\`.
>      .'// .-~"""""""~~~~-._   I | far._,-~~~~"""""""~-. \\`.

>  .'//______.============-..   \ | /   ..-============.______\\`.
>.'______________________________\|/______________________________`.

--
Scott F. Earnest           | We now return you to our regularly scheduled



Wed, 18 Jun 1902 08:00:00 GMT  
 EGA rows/cols?

Quote:

>I was thinking about the possibilities (because I enjoy playing with
>this) of making an EGA simulator for the old (ancient) Hercules video card.

>Now I'm not a super programmer, and was wondering if this was at all
>possible, or even has been done before. I know there are a number of CGA
>simulators for the Hercules Card, but I haven't seen any EGA.

A CGA emulator works by emulating the BIOS calls and copying direct
memory writes from the CGA screen (B800) to the Hercules screen (B000)
so that the visible effect is as close to effect on real CGA. That is at
least how I think they work.

When one emulates EGA the graphics page is on A000. There is no memory
there on a Hercules card, so the direct screen writes are wasted. With
a 386 one could put memory there, but who uses Hercules with a 386
class machine.

Also with the number of colors EGA has emulation is not that easy.

Osmo



Wed, 18 Jun 1902 08:00:00 GMT  
 EGA rows/cols?

: When one emulates EGA the graphics page is on A000. There is no memory
: there on a Hercules card, so the direct screen writes are wasted. With
: a 386 one could put memory there, but who uses Hercules with a 386
: class machine.

Errr....me, at the moment. I have a 386Dx/40, and a monochrome monitor
with Hercules display...I'm looking for a VGA monitor.

Don't blame me, it's been a weird couple of years.

Greg

--
                .-~~~~~~~~~-._       _.-~~~~~~~~~-.
            __.'  "Wanderer"  ~.   .~ wandered: on `.__
          .'//   names me the   \./ the Earth's back \\`.
        .'//  World; widely have |  I have travelled   \\`.
      .'// .-~"""""""~~~~-._   I | far._,-~~~~"""""""~-. \\`.

  .'//______.============-..   \ | /   ..-============.______\\`.
.'______________________________\|/______________________________`.



Wed, 18 Jun 1902 08:00:00 GMT  
 
 [ 5 post ] 

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