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M24SP DB25 to DB9 adapter

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    M24SP DB25 to DB9 adapter


    the Olivetti M24SP has the following D-Sub 25 RGB output (I assume its analogue and not TTL digital as it works with VGA):

    and the Philips CM11342 has the following D-Sub 9 TTL or analogue RGB input:

    I need to build an adapter to connect them. The M24SP follows the CGA standard expect for one 640x400x1bit mode which will not be used.

    How do I connect the PINs correctly? There is no INTENSITY bit mentioned on the DB25 side. The creator of the PDF couldnt couldn't help me.

    I know that there is a manual how to create a D-Sub 25 to VGA D-Sub 15 adapter:

    I already built it on my own and I have color without an INTENSITY bit (thus only 8 instead of 16 colors) - without touching PIN 2 and PIN 10 on Olivetti side, thus I assume that I can ignore those pins.
    MODE 0 could be INTENSITY but I am not sure..

    Thank you for your help
    Last edited by freakedenough; August 17, 2018, 11:00 PM. Reason: i am a polite person

    First own PC in 2003: AMD K6-2 500MHz, 320MB RAM, 40GB IBM HDD, 50x CD-ROM, 8x4x24 CD/RW, 100MBit LAN, 32MB ATi Rage 128 Pro, Windows XP

    Hello, M24, M24SP, Xerox 6060, AT&T 6300, Logabax Persona 1600 and M240 have analoque video signal, not digital. So you have to use a VGA capable monitor with your 25 to 9 pin adapter. CGA/EGA is digital monitor. The 9 pin layout must be done like VGA-9 connector. Or you make 25 pin to VGA-15 adapter.

    The difference between M24 and M24SP is, that it has the memory extension on the video board, so it can display the olivetti video mode not only in 640x400x1, but also in 640x400x16. Windows 1.0, 2.0, 3,0, GEM and some more software can support that. Addionally it has 10 MHz CPU and optionally FPU.

    M240 is the same power than M24SP (10 Mhz, 16 colors), but modernized mainboard (more compact) and more beautyful chassis.

    I also have working M24SP (and M24, M240)


      Since when does the at & t 6300, etc. have analog video? Well if that's true then it's news to me. And the thing you'll need in that case is an early multisync monitor.

      Back in the day, Taxan made several models, the numbers escape me at the moment, that were advertised to be AT & T 6300 compatible. These couldn't be analog video monitors. I'm really confused at this point.
      Last edited by 2icebitn; August 18, 2018, 07:33 PM.


        That was my reaction also. There are no DACs in the 6300 video boards. The schematics are on the M24 site, if you need verification.

        Schematics here; in particular, look at PDF page 37.

        Note that the output is very much like CGA. You have RGB output on pins 4,5 and 6 of J5 and "Highlight" on pin 7.
        Last edited by Chuck(G); August 18, 2018, 07:49 PM.
        Reach me: vcfblackhole _at_ protonmail dot com.


          Originally posted by 1ST1 View Post
          The difference between M24 and M24SP is, that it has the memory extension on the video board, so it can display the olivetti video mode not only in 640x400x1, but also in 640x400x16. Windows 1.0, 2.0, 3,0, GEM and some more software can support that.
          Well this is new to me, where can I find drivers? I currently have only monochrome 1bit under Windows when using the AT&T6300 driver that has been shipped with Windows.

          First own PC in 2003: AMD K6-2 500MHz, 320MB RAM, 40GB IBM HDD, 50x CD-ROM, 8x4x24 CD/RW, 100MBit LAN, 32MB ATi Rage 128 Pro, Windows XP


            The driver should be included in Windws. When I installed Windows in my M24, it was asking me if 1 or 16 colors. I choosed 1, as this was not M24SP. On M24SP I did not install Win yet.

            Here is a wiring diagram for VGA adapter. The VGA 15 pin connector used is a bit strange, as it is only 2 row connector.

            Generally usefull websites for M24:
            on the 2nd, you find a packet with software, using the special capabilities of M24 and M24SP.

            VGA Monitor support: Old NEC Mulitysinc 1 2A, 3D, or TVM, Mitsubshi multiscan monitos would do it, but they are hard to get now, most of the remaining ones should already be in good hands... Anyhow, you can try all VGA monitors you have, 640x400 isn't that strange and not too much different from 640x480 std VGA mode. Many of the old VGA monitors can for example display 640x400@70Hz ATARI ST monochrome mode with the correct ST-2-VGA-adapter. So, M24 at 640x400@60Hz should not be too difficult. Otherwise, some quite modern, cheap to get TFT can support a wide range of reslutions, eveb much more as their manufacturers write in the tech spec of the TFT. I recommend specially the NEC TFT Multisync 1990nxp and 1990fxp - these can support a lot analogue RGB signals from 15kHz PAL&NTSC video up to 1280x1024, up to 70Hz. I have two of them, and they 'eat' all what I gave them until now, except of interlaced mode of Comodore Amiga and Atari Falcon. The most exotic mine did display until now was ATARI TT highres monochrome mode, 1280x960@70Hz, by using an ECL to VGA adapter. Those NEC are in eBay here in Germany some times for just 20..25 bucks. Note, that the 17 inch models from NEC (17xx ?xp) are not that intelligent, but the 21 inch versions are that flexible as well.
            Last edited by 1ST1; August 19, 2018, 11:54 AM.


              Weren't you the guy who had the DEB card?


                It's been mentioned before that the M24 to VGA adapter only gets you 8 colors.

                With a little circuitry, you can get 16.
                Reach me: vcfblackhole _at_ protonmail dot com.


                  It should display 16 colors. The M24 video connector has no other video signal output besides RGB and H/VSync.

                  I didn't made this adapter yet, as I have one original mono and color monitor for my M24. But I was told that it is working fine by an italian friend, which is also present on this forum.


                    In what mode? These don't come with the ability to display 16 colors in high resolution. That's what the display enhancement board is for. You can do 640 x 400 monochrome. Possibly 16 colors at 320 x 200. And no one ever seems to discuss how compatible their CGA mode is, pretty so I'm to understand. Nor if their high color 640 x 400 mode is compatible with anything else (not is my guess).
                    Last edited by 2icebitn; August 19, 2018, 05:52 PM.


                      The M24SP used to have the DEP board by factory. That's besides the 10 Mhz the thing what makes it the M24SP. If your's has not, another owner of M24 has stolen it. I haven't opened mine yet, but I hope that it is complete. I already was happy that it was operationally.

                      The CGA mode is quite compatible to the standard, the M24 was one of the 1st XT clone which had highest compatibilty to IBM 5150, and beeing as twice as fast. The Olivetti modes are only compatible to itself, an own standard. Later there were some video cards from 3rd party which could emulate these modes. In one of my M370 there is an EGA card which has some jumpers to enable/disable these Olivetti modes.


                        I have an AT & T 6300. I want high resolution 16 colors.

                        Can you provide photos of the board?


                          Originally posted by 1ST1 View Post
                          It should display 16 colors. The M24 video connector has no other video signal output besides RGB and H/VSync.
                          but it doesnt. at least not for me. and trust me, i made the adapter 1:1 as mentioned in this manual. my assumption is that MODE0 pin is for intensity.

                          i got hands on a m24sp that had no scratches, no yellowing, nothing. it was like brand new. i got all manuals, etc. with it
                          and there is and was never a DEB card in it. i do not believe that they were shipped with DEB cards, no internet page ever mentioned that.

                          In Europe, Olivetti also launched a 10.0 MHz version: the Olivetti M24 SP, announced in November 1985,[10] a contender for the title of "highest clocked 8086 computer" as its processor was the fastest grade of 8086-2, rated for a maximum speed of exactly the same 10.0 MHz. To support this, the motherboard now featured a switchable 24/30 MHz master crystal, still divided by 3 to produce the 33% duty CPU clock, with an additional 4 MHz crystal to maintain that clock signal for peripherals that required it, and the video board receiving its own 24 MHz crystal to maintain the same image size and scan frequencies at both processor speeds.
                          Last edited by freakedenough; August 19, 2018, 12:24 PM.

                          First own PC in 2003: AMD K6-2 500MHz, 320MB RAM, 40GB IBM HDD, 50x CD-ROM, 8x4x24 CD/RW, 100MBit LAN, 32MB ATi Rage 128 Pro, Windows XP


                            Your original post states it follows cga. I doubt that's accurate. I'm not an expert, although I've had 4, I never connected 1 to a color monitor. My assumption is the mono and color monitors use similar frequencies (I know, the mono out put is 400 lines). But I would expect the color output to be also 400 lines, that is double scanned cga. In fact I'm sure of it, as the previously mentioned taxan monitors only accept 400 lines of res. And since the 640 x 400 mono mode is also available on a color monitor, pretty sure, a color monitor would have to be able to accommodate it.


                              We've been here before. A CGA monitor at 400 lines isn't going to work. An EGA one will, however.
                              Reach me: vcfblackhole _at_ protonmail dot com.