Full VGA Support For Modchips! Options

[netfraggel]

Punmaster has right that LM1881 has not standard h-sync signal but v-sync ist standard. I looked on the datasheet of the LM1881. On Pin1 the LM1881 output is c-sync (composite sync). Some displays cannot extract h-sync from the c-sync signal. But we can extract h-sync from v-sync and c-sync with a logic circuit.

RGBCV ---> RGBHV

CVH (csync,vsync,hsync TTL-Level)
---
000
010
101
110

h-sync has to be high if c-sync high and v-sync low

Now, if we use 7400 (four NAND) we may get h-sync (I dont know if the 7400 is fast enough).

The circuit:
- From LM1881 put c-sync and v-sync to the first NAND.
- The output of the first NAND and c-sync to the second NAND.
- Put the output of the second NAND to the third NAND (to invert the signal).
- The second NAND and the third NAND as intverter then build a logical AND.

See:

http://www.tkk.fi/Misc/Electronics/faq/vga2rgb/scart.html

at the end of the site for the circuit.

The LM1881 and 7400 are easy to get in many countries by private purchase.
This may be the solution to get hsync and vsync without the internal sync signals of the XBOX.
I am not sure but I think some very old Sun and Apple monitors need the c-sync instead of h-sync.
Excuse my poor english.

[yaywoop]

have you tried that circuit netfraggel?
it would probably be a good adition to the frosty vga cable, or a mod for people who need it.
i am sure there will be room inside the box
the only place i can get a lm1881 is over the net. and i cbf, so i will stick with internal signals

[patch6-]

Many thanks to all contributing to this issue.

Punmaster: I appreciate the explanation of the "video level corrector circuit", and am trying to build one, but the "break the three "discharge” traces and wire them instead to the three negative (inverting) inputs of the op-amps" direction doesn't show up on the schematic you posted (linking pins 1 to 16, 3 to 4 and 6 to 7, I'm assuming), though I've tried both and neither seem to work (the schematic first, then the rerouting of discharge traces). The fault could be due to my human error, but some clarification would be great.

[yaywoop]

@patch6- are you referring to http://forums.xbox-scene.com/index.php?s=&...t&p=4019291

so you have the evaluation board?

I didn't realize punmaster achieved this. using that circuit and the internal vga mod its possible to get *completely* standard vga out of the xbox

I wonder if the MAX4383 could be used instead of the LMH6739
unfortunately punmaster hasn't logged in for a month or so

hey frosty. did punmaster ever complete his ultimate tutorial? I was thinking about writing one but i quickly gave up

This post has been edited by yaywoop: Oct 4 2007, 12:59 AM

[FrostyTheSnowman]

hey frosty. did punmaster ever complete his ultimate tutorial? I was thinking about writing one but i quickly gave up

I honestly can't remember.

If you look back in this thread you will find out more about it, but I don't think he ever officially released his diagram...

Man, native VGA sure is a pain in the ass on the original XBOX...

[yaywoop]

i think SOG is good enough for most people. I mean it works ok on every LCD I have tested. and most people haveLCD's now.
its annoying. I did that internal sync mod and a few days ago I got a LCD that supports SOG.
yeah i found the post where he explains it
I think its pretty good that we can get any VGA output on a console that wasn't supposed to support it with such little hardware

This post has been edited by yaywoop: Oct 4 2007, 01:45 AM

[patch6-]

yaywoop: yes, that one

Has anyone reading this made a working version of the circuit in http://forums.xbox-scene.com/index.php?sho...p;#entry4019291 ?

[yaywoop]

@patch6- I will try making one of punmaster's circuits with a MAX4383 and tell you how it goes. I think 210Mhz will be enough.
I have not really done anything much with analog circuits before but tell me what your problem is and I might be able to help you

[yaywoop]

I can't really notice the white tint on my new LG LCD (new because my neighbors where throwing it out, I don't know why it works perfectly)
however I did notice the white tint on both of my CRT screens. so I will attempt the RGB level corrector anyway. it looks really easy.
I was going to make a transcoder with these max4383's but I can't find the resistors for it. maybe I will just make a level corrector and VGA switch all in one instead

[patch6]

Made the circuit again, taking care not to have loose connections or bridging debris, and there was no change. The video output is very blurred and stretched out horizontally when the wiring follows the diagram for LMH6739 on that previously mentioned post, kind of like looking through a thick glass bottle. That's without the power connected. When power is connected, pulling 5 volts and ground from the pc's power supply, the screen blanks out.

When the discharge traces are wired to the respective inverting negative inputs, the screen blanks out as well upon testing, with or without power.

The power seems to be fine, measuring at 5 volts steady.

The vga ports are also wired correctly, and work when the circuit is bypassed.

I might try replacing the chip.

[johannesleung]

I think everytime I post something here I will share for you and you work on vga bios frosty, its well deserved and awesome, Iam trying to use your last vga bios with force 480p on pbl on my xbox harddrive, I downloaded the one from your last release with the boot disc and extracted the bios with quix but I don't know why I cant tunr the bios into 256k size, it alwasy give me an error about not being able to extract on xbtool. Some help would be really welcome since I play plenty of emulators and often change my video game from tv (friends house) and lcd (my house) so I want to keep using pbl from my hd to switch into vga mode and play my games.

[yaywoop]

why do you want it to be 256k?? you aren't going to try flashing it are you?
you are not supposed to spit this particular X2 bios into 256 anyway.

[johannesleung]

hmmm I tough it was necessary since my modchip use 256k bios, the last release I was able to change it sizes into 256 tough, whatever I will try one more time with the 512k size bios, I tried one time before but it would not boot.

[FrostyTheSnowman]

I would burn the ISO for 'VGA Boot Disc v1.0' to a DVD and then copy the PBL BIOS off that disc using your XBOX.

Optionally, you an also try another utility called 'Simple xISO' to extract the files from the ISO.

NOTE: Whatever you do, DO NOT flash this PBL BIOS to any modchip.

[yaywoop]

hey frosty. why did you chose the 5035?