RGB megadrive cable thoughts

[simonbelmont2]

My RGB cable was created with informations from this page: http://www.mmmonkey.co.uk/console/sega/ms-md-scart.htm.
Today I find another page with another schematic for the RGB megadrive cable: http://members.optushome.com.au/eviltim/gamescart/megamstr.png
The only differences are :
- my cable have no capacitors;
- my cable resistor is 100Ω not 180Ω.
Does anybody know for what are used this capacitors? It's something wrong if I don't put this capacitors? What about the resistor?

Thanks!

[RGB32E]

Resistors and capacitors are listed on the datasheet from Sony for the video encoder (IC that outputs the video signal).  The Genesis/Mega Drive systems wire pins 23 (Red Out), 22 (Green Out), and 21 (Blue) out directly to the DIN connector without the capacitors and resistors.  Thats why when building cables they have to be added to get a proper video signal (per datasheet).   See attachment:

I can't comment on the 100Ω vs 180Ω, as I am not a PAL user... but it's my understanding that either value will work the same.

[albino_vulpix]

The only difference with the 100 and 180 ohm resistor is how much voltage is dropped in the scart pin 16. There is a range of voltages that will set the TV to RGB mode with pin 16. The 100ohm resistor sets the voltage to the lower end of the range, and the 180 volt to the higher. The only difference made is in power consumption. Any value between 100 and 180 will work equally as well.

[simonbelmont2]

Thanks for the informations. Yesterday I read about scart and find this good information:

- Pin 8 (Status & Aspect Ratio)  have 3 states:
0–0.4V → off
5–8V → 16:9
9.5–12V → on/4:3

- Pin 16 (Blanking signal/RGB-selection) have 2 states:
0–0.4V → composite
1–3V → RGB

Anyway I can manualy change my TV aspect ratio to be AUTO, 16:9, 4:3 and video signal to be AV 1; AV 2; F-AV; RGB and S-VIDEO so I don't need that resistor .

By the way, RGB32E do you have all the datasheets RGB for this consoles: Master System; Super Nintendo NTSC; Nintendo 64 NTSC; GameCube PAL; Playstation 1 PAL; Playstation 2 PAL?

[viletim]

simonbelmont2,

I chose the value of 180 ohms (1.5v) because a value lower than that is just wasting power with no extra benefit. The capacitors really shouldn't be left out - they are there for a good reason (though I won't bore everybody with the technical details). If you leave them out the encoder chip will run much hotter than normal, again, wasting power.

The Gamescart page lists the video encoder used along with datasheets for download near the bottom of the page. I've got the datasheets for a few more which I'll get around to uploading shortly. The CXA1145 and friends all need the resistor and capacitor in series with the video for normal operation.

[Hamburglar]

For what it's worth, I was getting vertical stripes on my Genesis 2 without the caps- after I fitted some caps in the connector the problem was gone.
Without the resistors in series with the RGB lines the picture was washed out on my Sony RGB monitor.

[RGB32E]

For what it's worth, I was getting vertical stripes on my Genesis 2 without the caps- after I fitted some caps in the connector the problem was gone.
Without the resistors in series with the RGB lines the picture was washed out on my Sony RGB monitor.

Adding resistors and caps to the RGB outputs is applicable to any Genesis/MD system.  On Sony RGB monitors (PVM) I've found that connecting a cap on the CSYNC output works well (otherwise the picture is off with the Genesis 2).  However, the CSYNC output from the Genesis 2 really needs buffering for other applications.

[Hamburglar]

Adding resistors and caps to the RGB outputs is applicable to any Genesis/MD system.  On Sony RGB monitors (PVM) I've found that connecting a cap on the CSYNC output works well (otherwise the picture is off with the Genesis 2).  However, the CSYNC output from the Genesis 2 really needs buffering for other applications.

How was your picture off? I had a similar problem, my cable was taking sync of off the composite video line on the Genesis, my monitor takes sync from composite video great with any console, but on the Genesis 2 I got a strange crosshatch looking pattern, added the cap and resistor the CXA1145 datasheeet  shows is needed with no luck, I ended up switching the sync line for the composite video line internally, (don't use composite video anyways)  fixed the problem.

[RGB32E]

How was your picture off? I had a similar problem, my cable was taking sync of off the composite video line on the Genesis, my monitor takes sync from composite video great with any console, but on the Genesis 2 I got a strange crosshatch looking pattern, added the cap and resistor the CXA1145 datasheeet  shows is needed with no luck, I ended up switching the sync line for the composite video line internally, (don't use composite video anyways)  fixed the problem.

The issue that I had initially with the Genesis 2 sync output was that the picture appeared much darker and had rainbow like noise (when fed to my PVM-2030).  When I added a 220uf cap to the sync output (from the 9 pin mini din), I got a perfectly stable and clear image.  When I tried using composite video for sync, I believe I got alternating vertical lines on the output image (light/dark/light/...).

However, adding a cap to the sync output didn't get very good results when connecting to my Kramer FC-14 RGB to component converter (high black level and additional noise).  I ended up using the sync buffer circuit that Redmond Cable used to sell with their PS1 RGB cables.  Hence, I've found two approaches to handled the funny sync output issue with the Genesis 2 - add a series capacitor to the sync line, or use a hex buffer (sync separator optional).