VOGONS


Arrived ISA 8 bit RTVGA boards

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Reply 20 of 33, by spark2k06

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Dimitri wrote on 2019-10-23, 10:44:

on the way another ISA8 VGA board - has Chips F82C451 or 82С452 with 256Kb RAM, datasheet says fully IBM CGA/MDA/EGA/VGA compatible.

I can't find the datasheet anywhere about RTG3105iEH, do you have any links?

I would like to make my own design based on this IC with some additional feature, and I have nowhere to start. Do you have any intention of sharing the schemes of your project? I like it because from what I can see from your photographs, few additional components to the IC are required.

Reply 21 of 33, by georgel

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Grzyb wrote on 2019-10-23, 22:16:
Generic VGA only offers basic compatibility with CGA modes, far from enough for those interested in playing CGA games. CGA games […]
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georgel wrote:

I don't think any VGA card requires additional utilities to provide CGA/EGA modes. They are just subset of the VGA spec.

Generic VGA only offers basic compatibility with CGA modes, far from enough for those interested in playing CGA games.
CGA games, when run on a VGA, tend to exhibit various problems, ranging from wrong pallete to not working at all.

So, when considering a VGA for PC/XT, it's very important to choose one with special CGA compatibility mode - which is chipset-specific, hence the need for additional utilities.

I've started playing on a CGA back then in late 80s. Never experienced any problem with running any CGA software on a VGA. Would you give an example of a vintage game that is running on CGA but not on VGA? Thanks.

Reply 23 of 33, by georgel

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jmarsh wrote on 2020-02-07, 11:43:

I remember having to use a utility to explicitly switch to CGA mode before playing Digger (the game with the popcorn background music).

I know it, of course. Here it is along with the source code: http://www.digger.org/download.html

Reply 24 of 33, by Grzyb

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georgel wrote on 2020-02-07, 11:34:

Would you give an example of a vintage game that is running on CGA but not on VGA?

Digger (and some other games by Windmill) - garbage
J-Bird - wrong palette, no palette effects
Popcorn - wrong palette
Round 42 - garbage

I recall CGA commonly criticized for its ugly cyan-magenta-white default palette.
Actually, many games use different palettes, but fail to do that when run on a VGA.
So, my rule for choosing a VGA for XT is: it must provide register-level CGA compatibility option.
Also, VGA chipsets with CGA compatiblity mode provide Hercules mode as well - which may come in handy sometimes, eg. Spacewar looks better on Hercules than on CGA.

Reply 25 of 33, by hyoenmadan

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georgel wrote on 2020-02-07, 11:34:

I've started playing on a CGA back then in late 80s. Never experienced any problem with running any CGA software on a VGA. Would you give an example of a vintage game that is running on CGA but not on VGA? Thanks.

Just because it runs and doesn't crash doesn't mean is running as it was intented to run. Specially if there are graphical glitches or faulty color palettes as described by Grzyb.

Reply 26 of 33, by spark2k06

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spark2k06 wrote on 2020-01-22, 12:39:
Dimitri wrote on 2019-10-23, 10:44:

on the way another ISA8 VGA board - has Chips F82C451 or 82С452 with 256Kb RAM, datasheet says fully IBM CGA/MDA/EGA/VGA compatible.

I can't find the datasheet anywhere about RTG3105iEH, do you have any links?

I would like to make my own design based on this IC with some additional feature, and I have nowhere to start. Do you have any intention of sharing the schemes of your project? I like it because from what I can see from your photographs, few additional components to the IC are required.

Ok, I see that this project is based on a reverse engineering work of one of the multiple fake 16bit ISA board PCBs based on RTG3105i (they are really 8 bits, the 16 bit bus is not used and only is there for to make the board a very low profile version). Also I bought one of these, and now I am in a position to carry out such reverse engineering work:

https://www.google.es/search?q=rtg3105i&tbm=isch

Reply 28 of 33, by Jo22

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Grzyb wrote on 2019-11-10, 12:22:
The only important difference was with Tunnels of Armageddon running in Hercules mode: […]
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The only important difference was with Tunnels of Armageddon running in Hercules mode:

* Realtek - monitor loses sync
* Trident - OK

So, Trident wins.
By a very narrow margin.

I don't know if this any helpful, but I tested Hercules compatibility of my OTI-37c with 3 Shades of Grey and an old Hercules C64 emulator.
As it turned out, Hercules emulation wasn't perfekt. But.. At some point the C64 emu ran fine on the old OAK (white),
whereas current DOSBox (orange) had graphical issues!
The pictures can be seen in OldCat's wonderful thread about his childhood embers build.
Re: "Childhood Embers" - 286 AT with Hercules graphics build

Edit: Some typos fixed.

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

Reply 29 of 33, by Jo22

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Grzyb wrote on 2020-02-07, 14:52:
Digger (and some other games by Windmill) - garbage J-Bird - wrong palette, no palette effects Popcorn - wrong palette Round 42 […]
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georgel wrote on 2020-02-07, 11:34:

Would you give an example of a vintage game that is running on CGA but not on VGA?

Digger (and some other games by Windmill) - garbage
J-Bird - wrong palette, no palette effects
Popcorn - wrong palette
Round 42 - garbage

I recall CGA commonly criticized for its ugly cyan-magenta-white default palette.
Actually, many games use different palettes, but fail to do that when run on a VGA.
So, my rule for choosing a VGA for XT is: it must provide register-level CGA compatibility option.
Also, VGA chipsets with CGA compatiblity mode provide Hercules mode as well - which may come in handy sometimes, eg. Spacewar looks better on Hercules than on CGA.

It hink the issue is related to register-level compatibility, which was very important in the beginning.
CGA games or programs that are either EGA/VGA-aware or use BIOS calls might display the other palettes, too.
Problem is, that most games did direct hardware access, because they were developed for speed with an XT classs machine plus a snowy CGA in mind.
On such a slow system, using BIOS calls for CGA or trying to detect EGA/VGA hardware or EGA/VGA BIOS perhaps didn't make much sense back in the mid-80s.
By the late 80s, this may had changed. But then, VGA was becoming the de-facto standard, anyway, so that only quality software was behaving nicely (on CGA).
Anyway, I'm speaking under correction here. My memories are a bit lacking here, also.
For further information, please have a look at this older thread.: Re: The year is 1990 and you still have a PC/XT and can't upgrade. Which games are you playing?

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

Reply 31 of 33, by matze79

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What does a Kit cost ?

https://dosreloaded.de - The German Retro DOS PC Community
https://www.retroianer.de - under constructing since ever

Co2 - for a endless Summer

Reply 32 of 33, by spark2k06

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spark2k06 wrote on 2020-02-16, 07:34:
spark2k06 wrote on 2020-01-22, 12:39:
Dimitri wrote on 2019-10-23, 10:44:

on the way another ISA8 VGA board - has Chips F82C451 or 82С452 with 256Kb RAM, datasheet says fully IBM CGA/MDA/EGA/VGA compatible.

I can't find the datasheet anywhere about RTG3105iEH, do you have any links?

I would like to make my own design based on this IC with some additional feature, and I have nowhere to start. Do you have any intention of sharing the schemes of your project? I like it because from what I can see from your photographs, few additional components to the IC are required.

Ok, I see that this project is based on a reverse engineering work of one of the multiple fake 16bit ISA board PCBs based on RTG3105i (they are really 8 bits, the 16 bit bus is not used and only is there for to make the board a very low profile version). Also I bought one of these, and now I am in a position to carry out such reverse engineering work:

https://www.google.es/search?q=rtg3105i&tbm=isch

Once the reverse engineering process has been carried out, here is the result ... 😀