Hardware > Hardware (Classic 16-/32-Bit)

ECL to VGA

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TXG-MNX:
Hello,

I am looking for an ECL to VGA convertor or schematic.

jens:
Hi.
Some people talked about that on the Atari Legend hardware forum.
Don't know about the status of this discussion though.

guest522:
Hi,

ich möchte diese Thema mal wieder in die Luft werfen, da unsere TTMs ja nicht besser werden.
Was ich bisher so an Diskussionen gelesen habe geht in Richtung:

ECL --> TTL --> VGA

Für die ECL --> TTL Konvertierung gibt es Bausteine wie den MC100ELT25 oder F100125DC.

Die Belegung für Mono ist:

15pin VGA-Stecker (TT030)  9Pin Monitor-Stecker (TTM194/195)

mono out +   Pin 4  <-----------> Pin 1
gnd                Pin 5  <-----------> Pin 7+8
gnd                Pin 10 <-----------> Pin 8+7
hsync            Pin 13 <-----------> Pin 3
vsync             Pin 14 <-----------> Pin 4
mono out -   Pin 15 <-----------> Pin 6


mono out + und mono out - gehen in einen ECL/TTL Konverter. Raus kommt dann ein 128,85MHz TTL Signal.
Doch was  dann?
Und....kann man das nicht direkt digital nutzen statt nach analog zu konvertieren?

ragnar76:
Hier mal ein Projekt von einem SUN User der das selbe Problem hat


--- Zitat ---The HSync and VSync signals are the usual TTL-level signals, so I can just wire them up 1 on 1. The actual video signal is more difficult as they are ECL: the non-inverted ECL output (without load connected) is -0.7 Volt for on, -1.7 Volt for off.
I've thought of 2 simple circuits to try to convert this: 1 very simple one which does not need a power supply and has quite a good chance of at least some success (but unlikely to give an excellent picture), and 1 less simple (but still only a handful of simple components), needing power independent from Sun and monitor, with smaller chance of any success, but potential for quite a good picture. I discarded the option of using official ECL-to-TTL chips because they're both expensive and need a symmetric power supply.

So this evening I had the opportunity to build the simpler circuit and try it. This one only involves a capacitor to connect the ECL+ with the Green VGA pin. My rough calculations showed 10 uF to be a nice value; to keep that one well-behaved on higher frequencies a 100 nF and 1 nF were added parallel to it.

Not wanting to risk my "good" monitor on it, I first used an old monitor with some problems (it makes some noises at random times, and the picture is always very noisy too, but you can see the general picture). Soon after powering up the Sun, the monitor lit up bright green, with clearly readable letters and a Sun-logo.

Wooooot!!

The noise on the screen made it difficult to judge the image quality delivered by my adapter, so I risked my good monitor on it. There were some strange but not very troubling effects near the left and right edge of the screen, and about 3 relatively minor ghost images. This would not only be usable for textmode, but probably also well-to-do for a windowing system! It's not really suitable to do an 8 hours/day job, but a nice baseline for me.

Connecting the capacitor not only to the Green but also the Red and Blue did of course give a black and white image that the original monitor would have had. The white was not really bright though; it was more of a light gray. This was not unexpected, but I had hoped the signal to have a bit more reserve. Nevertheless is was still very well readable, although the ghosting had gotten a bit worse too.

Addition of 2 antiparallel diodes between the VGA video lines and ground helped only barely noticably to improve the ghosting. I had hoped that by limiting the signal between +0.7 and -0.7 Volt the situation would improve a bit, but the signal doesn't really reach those levels. It could be worth a try to see what a germanium diode would do, limiting the signal to -0.3 Volt. But essentially the ghosting is caused by an impedance mismatch and cannot be resolved with only passive components without big losses to the signal strength (read: the white would become even darker).

Tomorrow I plan to try the somewhat more difficult circuit, I'm very curious if that one works in any way. I may also continue my research into Sun and PC keyboards. Today's research revealed that Sun keyboards are probably not too difficult, it's the PC keyboards that have quirks (some so stupid there's really not a single excuse for it). I hope I have a PC keyboard that supports mode 3 scancodes, looks like that would simplify stuff somewhat.
--- Ende Zitat ---

Auf den ersten Blick scheint es wohl zu reichen wenn man eine Hand voll Kondensatoren in die Schaltung wirft. Im endeffekt scheint es wohl so eine Bastelei zu werden wie den ST an VGA zu klemmen.

[Edit]
Quelle vergessen.
http://ars.userfriendly.org/users/read.cgi?id=18688&tid=120617

guest522:
Hi,
ja den Beitrag habe ich auch schon gefunden. Es ist aber wohl eher eine unbrauchbare Lösung wegen der erreichbaren Bildqualität. Leider hat der Kollege nicht weiter berichtet.
Mich wundert, dass es im Netz nicht was brauchbares zu geben scheint.

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