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freakedenough
August 25th, 2017, 11:03 AM
I always wondered why my Olivetti M24 SP (AT&T 6300) displays a light blue color with lines.
I found one "solution" via Google, but I'm not a English native and I simply do not understand what I should do now.


Source: ftp://ftp.oldskool.org/pub/drivers/ATT/6300/Documentation/Olivetti%20M24-240%20FAQ.html

Let's look at the monitor. If you have a monochrome monitor can be connected to ground on pin 2 on DB25 jack Olivetti video card,
so you believe to be attached sheet for a color screen and remove the underscore attribute on some color
combinations from place to strange horizontal stripes.

What exactly does that mean? What do I have to do to get rid of the lines (blue color is always a problem, see attachments)?
Connect PIN 2 to any other GND PIN on the card itself or what?
ftp://ftp.oldskool.org/pub/drivers/ATT/6300/Documentation/video_pinout.pdf

Thank you!

1ST1
September 11th, 2017, 11:22 AM
I don't see well what you mean. Which monitor do you use?

By the way, besides M24 and M240 I also have a M24SP. Are you in Germany?

freakedenough
September 15th, 2017, 04:06 AM
Hey 1ST1,

I live in Austria.
My problem is that a "light blue" text is always displayed with an underlined attribute. I'm using the original Olivetti M24 Monochrome Monitor.

1ST1
September 15th, 2017, 11:40 PM
Die you tryed the display test functioms of m24/at&t6300 customer test disk and checkit 3.0?

vwestlife
September 16th, 2017, 11:43 AM
It's intentional. The IBM Monochrome Display Adapter shows blue text as underlined. Thus Olivetti is correctly emulating MDA.

Chuck(G)
September 16th, 2017, 01:11 PM
When you're in monochrome, you don't have colors; you have "attributes". (invisible, underline, bright, blinking and reverse) See John Elliott's discussion (http://www.seasip.info/VintagePC/mda.html). It's also in the IBM techref and numerous other places.

freakedenough
October 1st, 2018, 12:17 PM
Ok guys, just for the dozens of people that find this thread via Google:
The simple solution is to connect PIN2 of the CGA card to GND. I connected the 2nd end to the chassis by clamping it between the slot brackets, this allows me to easily revert the change if needed. So far no negative consequences...
48383 48384

result:
48385 48386

1ST1
October 1st, 2018, 12:25 PM
Have you had a look onto the dip switches?

Type DIPSW1/5 DIPSW1/6
IBM B/W display Off Off
40 x 25 Off On
80 x 25 On Off

freakedenough
October 1st, 2018, 12:54 PM
Sure but that alone didnt help since you also need to ground PIN2 to make this thing believe that it has a color monitor attached.

Valerio
October 1st, 2018, 03:13 PM
I always wondered why my Olivetti M24 SP (AT&T 6300) displays a light blue color with lines.
I found one "solution" via Google, but I'm not a English native and I simply do not understand what I should do now.


I think one of the problems is the somewhat liberal :) translation of the page you quote from the original Italian (http://www.retrocomputing.net/info/faq/Olivetti_M24-240_FAQ.html) version:


Se avete un monitor monocromatico potete collegare a massa il pin 2 sulla presa DB25 della scheda video Olivetti, in tal modo si fa credere alla scheda di essere attaccata ad uno schermo a colori e si elimina l'attributo di sottolineatura che su certe combinazioni di colore da luogo a strane striature orizzontali.


If you have a monochrome monitor, you can tie pin 2 to ground on the DB25 connector of the Olivetti video card. In this way you'll have the video board believe it is connected to a colour monitor, and it will disable the underline feature that, in some colour combinations, gives rise to strange horizontal stripes.

This is indeed supported by the Theory of Operations manual which indicates that pins 2 and 10 are used by the system to identify what kind of monitor is connected. They are both internally pulled up to Vcc through resistors, so connecting them to ground externally (any ground pin on the DB25 connector, ie 14 to 21, is fine) is safe. The configuration with pin 2 tied to ground (and pin 10 left alone) corresponds to a colour monitor.

Trixter
October 2nd, 2018, 10:35 AM
Previous response is 100% correct, and was what I was going to post -- thanks for beating me to it :-)

To the OP freakedenough: The underline is part of the M24's charm, and software made for the M24 will occasionally use that. I would have suggested to connect a VGA monitor instead; a simple adapter can be wired up, and then you'll also have color.

freakedenough
October 2nd, 2018, 11:02 AM
ugh! the vga adapter is an urban legend and allows only 8 colors and works only with a few vga screens that support 25khz
http://www.vcfed.org/forum/showthread.php?65253-M24SP-DB25-to-DB9-adapter&p=530626#post530626

please read this related thread and you will understand that the vga adapter is the worst solution.

Trixter
October 2nd, 2018, 12:23 PM
It's not an urban legend, it works to display 8 colors. 16 shades of green, or 8 shades of color -- you get to decide which is the worse trade-off. For any CGA graphics game, the missing intensity is not that big a deal; it's only a problem in 16-color text mode.

vwestlife
October 2nd, 2018, 01:58 PM
It's not an urban legend, it works to display 8 colors. 16 shades of green, or 8 shades of color -- you get to decide which is the worse trade-off.
But only if your monitor supports the 25 kHz scan rate. You've claimed several times that the PC6300/Olivetti's video output is 31.5 kHz (same as VGA), but the info I can find from old Usenet posts says it's 25 kHz.

In fact, there were several aftermarket video cards, as well as AT&T's own VDC750 card, which allowed you to output 630x350 EGA video at 25 kHz, so that AT&T and Olivetti users could add EGA compatibility without needing to replace their monitor.

Trixter
October 2nd, 2018, 07:14 PM
But only if your monitor supports the 25 kHz scan rate. You've claimed several times that the PC6300/Olivetti's video output is 31.5 kHz (same as VGA), but the info I can find from old Usenet posts says it's 25 kHz.

I've never claimed it was 31.5 KHz. (If you can find a post where I specifically said it output 31.5 KHz then I'll apologize, but I don't think I've ever written that.) I've only claimed you can hook up a VGA monitor, and that was based on Chuck's anecdote (I've never tried it; he did). Also, these days, I think it would be assumed that a scan converter of some sort would be part of the mix, since no monitor made in the last decade supports horizontal rates that low.

When I perform TTL to analog conversion, it's always for the purpose of capturing video footage. I only use period-accurate monitors with my systems for regular display use.


In fact, there were several aftermarket video cards, as well as AT&T's own VDC750 card, which allowed you to output 630x350 EGA video at 25 kHz, so that AT&T and Olivetti users could add EGA compatibility without needing to replace their monitor.

Indeed, and I have one. One notable thing about about that card is that it retains the original M24 400-line mode, so that software written for either will work. Also notable: The PVGA1A-based card that came with an AT&T 6286 also retained the 640x400x2 mode for compatibility, although the DEB 16-color variants are not emulated, only the black-and-white mode 40h.

Chuck(G)
October 2nd, 2018, 07:36 PM
Didn't most Japanese PC98 color systems also use 640x400 initially? I believe the APC marketed in the USA was closer to 480.

vwestlife
October 2nd, 2018, 07:53 PM
I've never claimed it was 31.5 KHz. (If you can find a post where I specifically said it output 31.5 KHz then I'll apologize, but I don't think I've ever written that.)
It's on your web site: https://trixter.oldskool.org/2008/04/22/beefing-up-your-6300/

"You are correct that connecting any VGA monitor to a stock 6300 is not only possible, it is easy! The mode used by the M24/6300 was double-rate (horizontal is 31.5KHz) which is compatible with VGA. You can literally wire up an adapter and it will work without any modification."

Trixter
October 2nd, 2018, 07:59 PM
No idea why I wrote that. Thanks for bringing it to my attention; I've removed that incorrect phrase.