Interesting.

reading it without clicking the links, I was already suspecting the pinout to be for an M24, which has something like CGA output if i recall correctly.

Can you share some more details on the monitor you have, if any are available?
Worst case, i think, opening up the monitor and figuring out the pinout of the connector from where all the wires end up.

edit: nevermind. I don't know what to do with the SR and SB.

Highlight should correspond to Intensity and it appears that since there are no other intensity inputs, the monitor cannot show full 64 colors of EGA in the high resolution mode...

Tiido wrote on 2025-09-12, 21:31:

Highlight should correspond to Intensity and it appears that since there are no other intensity inputs, the monitor cannot show full 64 colors of EGA in the high resolution mode...

Correct. The manual states 16 color in 640x350. I'd assume that means 16 colors at the same time out of a palette of 64, that matches the specifications of the Olivetti with the Display Enhancement Board (DEB) installed which the monitor is designed to run with.

I btw found the pinouts in an old usenet post here: https://groups.google.com/g/comp.sys.att/c/x6 … /m/77DQS7kOHUIJ

Subject: Pinout for Taxan 9 pin Bob Eberly / George Wilkin to 25 pin AT&T cable […]
Show full quote

Subject: Pinout for Taxan 9 pin Bob Eberly / George Wilkin
to 25 pin AT&T cable

How to make a cable to connect the 318 to the TAXAN or STB Card.

The connections for a 318 to these cards should follow this example which
is for a TAXAN 557 Gold Card. (The Paradise Card will NOT work with the
318 monitor.

The pinouts to connect the AT&T 318 monitor with the 25 pin connector to
a Taxan Gold Card (9 pin) are as follows:

25 9 Lead
PIN PIN Designation

1 8 H. Sync
2 1 SG
3 9 V. Sync
4 3 Red
5 4 Green
6 5 Blue
7 6 Intensity
8 7 NC
9 - NC
10 - NC
11 - NC
12 - NC
13 - Degauss
14 2 SG
15 2 SG
16 2 SG
17 2 SG
18 2 SG
19 2 SG
20 - NC
21 - NC
22 - NC
23 - NC
24 - NC
25 - NC

SG = Signal Ground
NC = No Connection

vetz wrote on 2025-09-12, 21:44:

I'd assume that means 16 colors at the same time out of a palette of 64

With only 4 digital signal lines it could only support a fixed palette of 16 colors rather than a custom palette.

DEB does temporal dithering on the 4 RGBI TTL pixels from the internal LUT dictated by the palette choice.
It is the same principle as EGA cards outputting to MDA monitors, just used in colour scenario.

Likewise, M19 uses same approach to achieve a fixed 16-shade CGA palette on its MDA-standard monitor in M24 640x400 compatible programming.

The DEB itself is 4 bit output so a normal RGBI monitor is fine, the card will do its magic in showing more than 16 colours on it (could flicker tho)

Ah, a personal holy grail that I have been seeking for decades as well! 😄

A number of years back, I acquired an ATI EGA Wonder 800 (non-plus) card for the exact same reason. Like the STB Multires, it supports Olivetti M24 (and M28?) 25kHz ("400 line" ) monitors.

According to the manual of the EGA Wonder (which as far as I understand also applies to the EGA Wonder 800 non-plus), it actually supports the different EGA palettes beyond the standard 16-color CGA palette, and it apparently uses pulse-width modulation (PWM) techniques to accomplish this. @zb10948, is this the same as the temporal dithering technique you mentioned? I believe so, because indeed, it's the same technique that some EGA cards (including the EGA Wonder) use to show 16 shades of grey on MDA monitors.

In addition to that, it also supports the Hercules monochrome graphics mode on these monitors.

And to top all of that off, the EGA Wonder even supports a non-standard higher 752x410 resolution mode on these 25kHz Olivetti monitors. Drivers for this mode exist for Windows, GEM and AutoCAD.

I'm not sure if the STB Multires supports a similar higher resolution mode.

Years before that, long before I even got a suitable card for it, and before the internet had become common, we had even soldered a 9-pin/25-pin adapter based on a pin-out that we got from someone. But I never came around to trying all of this out.

And the PSU of my Dad's M24 stopped working a few years ago, so I haven't been able to test it on that machine. I've always wanted to see how 16-color graphics (especially high-resolution 16-color graphics!) would look on the monitor that came with that M24. The M24's built-in graphics adapter never took full advantage of the monitor's true capabilities, and that was something that always frustrated me as a kid.

I guess I could try the monitor with the EGA Wonder card in another computer, but the monitor hasn't been turned on in years. We have preserved it, but I hope it will turn on without any black smoke if we try it. 🤞🏼

This was actually one piece of the puzzle for getting EGA to work in the M24. Apparently we were lucky to have the newer revision of the M24 that allows the on-board graphics to be switched off with a jumper setting. It also requires a BIOS update to fix EGA compatibility, but I managed to obtain the BIOS chips for those.

I should probably verify with a multimeter if the wiring of that that soldered adapter is correct.

This is really a project that I'd like to finally complete. I really should get that PSU fixed. Likely a matter of replacing caps. Not something that I have experience with. Maybe I should just replace and bypass the original PSU. It's an older PSU, and quite noisy.

Happy to continue sharing more knowledge and experiences on this topic here.

zb10948 wrote on 2025-09-12, 22:57:

DEB does temporal dithering on the 4 RGBI TTL pixels from the internal LUT dictated by the palette choice. It is the same princi […]
Show full quote

DEB does temporal dithering on the 4 RGBI TTL pixels from the internal LUT dictated by the palette choice.
It is the same principle as EGA cards outputting to MDA monitors, just used in colour scenario.

Likewise, M19 uses same approach to achieve a fixed 16-shade CGA palette on its MDA-standard monitor in M24 640x400 compatible programming.

The DEB itself is 4 bit output so a normal RGBI monitor is fine, the card will do its magic in showing more than 16 colours on it (could flicker tho)

Thanks for the information! I didn't know this previously.

digger wrote on 2025-09-13, 00:14:

In addition to that, it also supports the Hercules monochrome graphics mode on these monitors.

And to top all of that off, the EGA Wonder even supports a non-standard higher 752x410 resolution mode on these 25kHz Olivetti monitors. Drivers for this mode exist for Windows, GEM and AutoCAD.

I'm not sure if the STB Multires supports a similar higher resolution mode.

The STB MultiRes as far as I know do not have a driver to go to 752x410 (atleast it's not shipped with the card). I was on the lookout for either an ATI EGA Wonder or the STB MultiRes. Coincidence made it so that I ended up with the MultiRes.

digger wrote on 2025-09-13, 00:14:

This is really a project that I'd like to finally complete. I really should get that PSU fixed. Likely a matter of replacing caps. Not something that I have experience with. Maybe I should just replace and bypass the original PSU. It's an older PSU, and quite noisy.

Happy to continue sharing more knowledge and experiences on this topic here.

Please do! I was hoping you'd see this topic as I know you're knowledgeable on this subject. Hope you also get your M24 into working condition!

digger wrote on 2025-09-13, 00:14:

A number of years back, I acquired an ATI EGA Wonder 800 (non-plus) card for the exact same reason. Like the STB Multires, it su […]
Show full quote

A number of years back, I acquired an ATI EGA Wonder 800 (non-plus) card for the exact same reason. Like the STB Multires, it supports Olivetti M24 (and M28?) 25kHz ("400 line" ) monitors.

According to the manual of the EGA Wonder (which as far as I understand also applies to the EGA Wonder 800 non-plus), it actually supports the different EGA palettes beyond the standard 16-color CGA palette, and it apparently uses pulse-width modulation (PWM) techniques to accomplish this. @zb10948, is this the same as the temporal dithering technique you mentioned? I believe so, because indeed, it's the same technique that some EGA cards (including the EGA Wonder) use to show 16 shades of grey on MDA monitors.

In addition to that, it also supports the Hercules monochrome graphics mode on these monitors.
.
.
.
Happy to continue sharing more knowledge and experiences on this topic here.

Hi digger,

I've probed into M19's dithered signal.
As you can see in attachment the Video and Intensity lines have uneven TTL periods. In normal TTL video, a TTL pixel 'period' can be either high or low.
In this TTL video we have flipping of the pixel line while in the pixel period. I think this achieves the effect shown in this gif - https://en.wikipedia.org/wiki/File:Green_and_ … l_FRC_4K60.webm

The analog reading attachment is I/V after a lo-pass, this is the actual driver of the beam. On analogue level it looks like strobing which corresponds to above.

I have also been running 800+ on my M19. Did not scope it, judging by cause-and-effect, it is the same thing.

I've always suspected same thing can be accomplished for RGBI screens.

800+ does the dithering slightly faster but I cannot say for certainty because as I do not have proper CRT measurement gear, I can know only averages that come from the card's register.
Some colour values flicker more than others. Their TTL alteration cycle is slower hence they redraw slower and flicker quite a lot.
CGA_comp measures almost stable 45 Hz for M19 video and janky 47 Hz for ATi.

However M19 internal video does a far better way of 16-to-MDA adaptation for this screen, regardless of ATi having a control utility. No setting there works as good as internal M19 video.

I suspect getting a proper 64 to 16 conversion would require a lot of luck on the RGBI monitor choice. The integrated solutions (gfx+monitor) like M19 work as they're tuned to each other.

Wow, thanks for the very thorough analysis of the signal and your detailed findings, @zb10948!

With "800+", do you happen to mean the EGA Wonder 800+ (Plus)? Because the 25kHz monitor support was apparently dropped in the 800 Plus. It has a newer chipset that is very different from that of the 800 non-plus. The chip on the 800+ (and later ATI cards) has the ATI logo printed on the main chip. In contrast, the original EGA Wonder and EGA Wonder 800 non-plus have a CHIPS (Chips & Technologies?) logo on the main chip.

As far as I have been able to find out from on-line research, the EGA Wonder cards based on the CHIPS chip support 25kHz (400-line) monitors through a jumper setting, whereas cards based on the ATI-branded chip (such as the 800 Plus and later EGA/VGA Wonder cards) do not.

I also have a VGA Wonder-16 that has both 15-pin analog VGA and 9-pin TTL ports and I have been using that to get EGA graphics with 16 shades of grey on an IBM 5151 MDA monitor. That card also does not support 25kHz 400-line monitors, even through the TTL port. I guess the market was too small for ATI to continue implementing that feature on their later graphics chip designs.

The M19 doesn't have a 25kHz monitor like the M24 does, right?

The adapter cable is ready to be tested!

Huge thanks to Tiido for helping out building this.

digger wrote on 2025-09-14, 10:42:

Wow, thanks for the very thorough analysis of the signal and your detailed findings, @zb10948! […]
Show full quote

Wow, thanks for the very thorough analysis of the signal and your detailed findings, @zb10948!

With "800+", do you happen to mean the EGA Wonder 800+ (Plus)? Because the 25kHz monitor support was apparently dropped in the 800 Plus. It has a newer chipset that is very different from that of the 800 non-plus. The chip on the 800+ (and later ATI cards) has the ATI logo printed on the main chip. In contrast, the original EGA Wonder and EGA Wonder 800 non-plus have a CHIPS (Chips & Technologies?) logo on the main chip.

As far as I have been able to find out from on-line research, the EGA Wonder cards based on the CHIPS chip support 25kHz (400-line) monitors through a jumper setting, whereas cards based on the ATI-branded chip (such as the 800 Plus and later EGA/VGA Wonder cards) do not.

I also have a VGA Wonder-16 that has both 15-pin analog VGA and 9-pin TTL ports and I have been using that to get EGA graphics with 16 shades of grey on an IBM 5151 MDA monitor. That card also does not support 25kHz 400-line monitors, even through the TTL port. I guess the market was too small for ATI to continue implementing that feature on their later graphics chip designs.

The M19 doesn't have a 25kHz monitor like the M24 does, right?

Hey digger, you're correct, I checked my EGA Wonder 800+ manual and it doesn't support 25kHz monitors. The C&T chip is true EGA I believe, the ATi chip is generic. I think that your VGA Wonder-16 is a 16 bit version of the VGA card "Edge" which is full version of EGA Wonder 800+. Or better said, EGA Wonder 800+ is a cut down version (no RAMDAC, resistor network and analog video port) of VGA Edge with an EGA BIOS.

M24 is usually hooked directly to VGA screens because they can usually tune down that 6kHz by manual setting.

My M19 monitor is standard MDA 50 Hz 18kHz screen, yet it can display 45 Hz, and can probably also display a range of hsync around 18kHz.

I don't see why one shouldn't try running M24 screen at a bit lower (EGA 22kHz), or even VGA 31.5 freq if lucky.

I guess the problem with EGA Wonder 800+/VGA Edge/VGA Wonder-16 and all autodetection type cards is the autodetection of monitor.
Maybe a card with manual selection could be operable.

Could the same type of monitor be tuned up to accept VGA?

Success!!

Oh wow, that's so cool! 😍

Interesting detail: Olivetti monitors (at least the 25kHz 400-line ones that came with the M24) lacked the special circuitry that the original IBM CGA and EGA monitors (and most CGA and EGA clone monitors) implemented to display dark yellow as brown. Therefore, on Olivetti monitors, what's supposed to be brown is shown in a mustard-like color. I think you can see that in the "DUKE NUKUM" title in your screenshot.

Anyway, can I order a cable like the one that you and Tiido built for this? It looks so much sturdier and well-built than the adapter I soldered together back in the day, and I don't even know if that was properly or correctly done. I'd rather not take the risk.

Thanks! 🙏🏼

digger wrote on 2025-09-15, 00:16:

Oh wow, that's so cool! 😍

Yeah! I don't think anyone has seen this since the 80-90s!

digger wrote on 2025-09-15, 00:16:

Interesting detail: Olivetti monitors (at least the 25kHz 400-line ones that came with the M24) lacked the special circuitry that the original IBM CGA and EGA monitors (and most CGA and EGA clone monitors) implemented to display dark yellow as brown. Therefore, on Olivetti monitors, what's supposed to be brown is shown in a mustard-like color. I think you can see that in the "DUKE NUKUM" title in your screenshot.

I was under the impression here that the issue was the implementation of CGA in the video card, not the capability of the monitor. The brown color in Duke Nukum might be due to overexposure on my phone camera. I took a much better representation of the colors for Planet X3. I'll check later!

digger wrote on 2025-09-15, 00:16:

Anyway, can I order a cable like the one that you and Tiido built for this? It looks so much sturdier and well-built than the adapter I soldered together back in the day, and I don't even know if that was properly or correctly done. I'd rather not take the risk.

Thanks! 🙏🏼

The cable was made out of spare parts from serial/parallell connectors from AT motherboards/cases. Need to check if I have more, but I don't think it should be possible to damage anything in the monitor on a TTL/digital signal if it's not done correctly. If you get your PSU fixed, then reach out on PM.

zb10948 wrote on 2025-09-14, 12:23:

I guess the problem with EGA Wonder 800+/VGA Edge/VGA Wonder-16 and all autodetection type cards is the autodetection of monitor.
Maybe a card with manual selection could be operable.

IIRC, the ATI EGA Wonder 800+ uses a simple 74LS245 bus transceiver for monitor detection.
The thing is that EGA changed the meaning of pin 2 from a secondary GND to RED0.
Since TTL inputs are internally pulled high, “reading from” the video output port will then return a “1” in that position if a non-CGA monitor is connected.
That does not explain how exactly it can distinguish between EGA and MDA monitors, but i assume that it might write “0” bits and then quickly try to read them back to tell the difference between TTL data inputs and N/Cs.

Hi Benedikt,

The card definitely does things with monitor H/V in its BIOS code, it takes few seconds for MDA monitor to be detected and it does slightly hiss meanwhile (doesn't seem too dangerous by the sound of it).
My "power on picture displayed" time with this card is ~5 secs longer compared to onboard video due to this phase.

Benedikt wrote on 2025-09-15, 10:55:

IIRC, the ATI EGA Wonder 800+ uses a simple 74LS245 bus transceiver for monitor detection. The thing is that EGA changed the mea […]
Show full quote

IIRC, the ATI EGA Wonder 800+ uses a simple 74LS245 bus transceiver for monitor detection.
The thing is that EGA changed the meaning of pin 2 from a secondary GND to RED0.
Since TTL inputs are internally pulled high, “reading from” the video output port will then return a “1” in that position if a non-CGA monitor is connected.
That does not explain how exactly it can distinguish between EGA and MDA monitors, but i assume that it might write “0” bits and then quickly try to read them back to tell the difference between TTL data inputs and N/Cs.

I did notice that the monitor auto-detection process would take a noticeably long time from startup, when the IBM 5151 MDA monitor was connected to the 9-pin TTL output port of the VGA Wonder-16. But it would ultimately initialize and show proper output on that monitor.

"CGA brown" is definitely handled in the monitor not the video card

It 'could' be incorporated as a simple logic gate + buffer pcb in these home-made adapters, since they are intended for use on monitors that lack the circuitry.

Maybe add a switch to enable/disable the feature.

All it needs to do is catch when certain logic levels are high/low, then output a new logic state/pattern while true. Logic chips are plenty fast enough these days.