kao wrote:

The second line is only necessary on true blue IBM CGA cards since you must set the border to a nonblack color in 80-column text mode or you'll get a B&W picture (a hardware bug that does not occur on the PCjr, Tandy, and all CGA clones)

I assume you're referring to the composite output? As far as I'm aware, the border color must specifically be #6. While a border of any color (other than black/grey/white) can work around the 80-column hardware bug by doubling as a color burst signal, color #6 just happens to be close enough to NTSC specs (in terms of phase and amplitude) to produce correct colors.

I assume you're referring to the composite output?

Yes.

As far as I'm aware, the border color must specifically be #6. While a border of any color (other than black/grey/white) can work around the 80-column hardware bug by doubling as a color burst signal, color #6 just happens to be close enough to NTSC specs (in terms of phase and amplitude) to produce correct colors.

Actually you can set the border to anything you want, but values other than 6 or 15 will result in the colors being tinted (meaning everything will have a red, blue, purple, green etc tint to it).

For some reason, the 80-column border is always a shade of yellow in composite mode as well.

Got coolhaken's PM message. Dunno about Boulder Dash Construction Kit, so I can't really help you there. BTW, you say it flickers on DOSBox.

I have a Hercules card, but I can't test the game out because it's in a Pentium and SIMCGA programs only work if the HGC is the lone video card in the computer.

hgcibm is not so good, how have you configured it?
http://www.sorgonet.com/8086/CGA_emulation/
In my opinion the "emu.exe" is by far the fastest and best looking cga-emulator on a hercules card.

HGCIBM is terribly slow.

Doc

ripsaw8080 wrote:

Some CGA games work on Hercules graphics with CGA simulator programs, but many do not; it depends on the extent to which they directly interact with the CGA hardware. A typical hangup is vertical retrace, but other issues are possible. In the case of Digger, it activates 320x200 graphics by writing to the CGA mode register, not by calling BIOS to set mode 4.

As with vertical retrace, it is possible to work around the mode change by hacking. In DIGGER.COM search for the byte pattern BA D8 03 B0 02 EE and change it to B8 04 00 CD 10 90; in the program file I have here the pattern starts at offset 38F. The hack changes the mode register write to a call to INT 10h to set mode 4. It seems to work OK in my tests in DOSBox, but please reply with how you fare on your real system.

Hi and thx!

Does it work for other CGA titles?
Do you see any chances for making a faster CGA emulation with a hercules card?

kao wrote:

Vertical retrace causes problems on VGA too because it's 70Hz on there while CGA is 60Hz. While this won't prevent games from running, a lot of them like Alley Cat and Sierra titles have choppy animation. In the case of Hercules, you have a bigger problem because the refresh on there is 50Hz (slower than CGA).

The problem is bigger than that:
Hercules has the status register on another port, and uses a different bit to signal vsync. I believe the bit is also 'inverted' compared to how it is used in CGA/EGA/VGA.

Which means that if you try to poll for vsync on the CGA/EGA/VGA status register, you're reading from an unused port, and you'll get stuck in the loop forever.
You'd have to patch the code to use the correct port and polling logic on Hercules... and then you still have the 50 Hz issue as you pointed out.

kao wrote:

The second line is only necessary on true blue IBM CGA cards since you must set the border to a nonblack color in 80-column text mode or you'll get a B&W picture (a hardware bug that does not occur on the PCjr, Tandy, and all CGA clones)

This is only for composite. And the reason for this is that the timing of 80-column mode is not compatible with the colorburst signal. Because the display logic has to be clocked higher in 80-column mode, the timing gets messed up, and the scanline starts during the colorburst signal.
That is why they disable the colorburst, because otherwise the display can lose sync and the image becomes unstable. People discovered that many TVs/monitors would work with the 'broken' colorburst if you use certain background colours, because the TV/monitor would mistake that for the colorburst, and it would sync properly.

IBM probably figured that it wasn't worth the trouble of fixing this at the time, because the high resolution of textmode meant that it would create lots of artifacts anyway, and text wouldn't be readable with composite.
If you wanted 80-column mode in colour, you should use RGBI.

They might have fixed it for PCjr because it was a home computer, meant to be used with a TV. Besides, they overhauled the graphics chip anyway, and added various features.

Hm okay that's why EMU0 dos not work on real hercules-monitor, because it "tweaks" to 60hz. On my EUM-1491A this CGA emulator works.
But I love the original "berstein monitor" the multiscan looks more like "grey" then "bernstein".

btw: ​DemoScene-Demo, Slide-Show, Music-Discs, Win1x etc:
https://www.youtube.com/watch?v=nhcW2MNL7Zo

next vid will feature some cga-emulated games...

btw: http://www.vcfed.org/forum/showthread.php?540 … raphics-Thread-)