DC VGA out Qs

[mesmer]

What is the purpose of the circuit on the H and V sync in this schematic?
http://www.mmmonkey.co.uk/console/sega/dc-vga.htm

What is the difference between that in the IC in this one?
http://www.gamesx.com/grafx/dricas.gif

If I want to build a VGA box for a tri-sync arcade monitor, can I just wire CSYNC from the DC to the HSYNC on the VGA connector?

Thanks

[antron]

the top one is a pull-up resistor and a current limiter. probably required.

the bottom one adds a buffer (probably improves compatability/stability?)

why not use H and V in your box? then you could use it with any VGA monitor and not just one that can take CSYNC.

[RGB32E]

What is the purpose of the circuit on the H and V sync in this schematic?
http://www.mmmonkey.co.uk/console/sega/dc-vga.htm

What is the difference between that in the IC in this one?
http://www.gamesx.com/grafx/dricas.gif

If I want to build a VGA box for a tri-sync arcade monitor, can I just wire CSYNC from the DC to the HSYNC on the VGA connector?

Thanks

Yeah, I'll be exploring this myself this weekend... The gamesx implementation looks like a standard hex buffer for buffering the sync signal (ensuring proper levels - normalizing the sync signals from the dreamcast).

UPDATE:

http://forum.arcadeotaku.com/viewtopic.php?f=26&t=1870

So....

1. Buy a generic DC VGA box
2. Open it
3. Disconnect (cut) wire connected to pin 6 on the DC connector
DONE

The sync config would be separate H and V, not composite sync. Your arcade monitor should/could accept both types (H/V or CSync).

Wasn't that easy?

[mesmer]

1. Buy a generic DC VGA box
2. Open it
3. Disconnect (cut) wire connected to pin 6 on the DC connector
DONE

I was thinking of making my own because the 1st party ones are expensive, and I've heard some of the 3rd party ones are low quality, while some are just fine. Didn't feel like rolling the dice on a 3rd party one.

Also, they say that sometimes pins 6&7 are both tied to ground at the A/V plug, so you can't put a switch in the box to enable low res for Bangai-O, etc.

Using both H&V make sense, just curious about CSYNC. I assume it would need the same type of circuit.

[RGB32E]

Yeah, if pins 6 & 7 are tied together, the plastic hood on the DC plug can be slid off, and the bridged pins unbridged! However, that scenario would likely only occur on VGA ONLY DC VGA boxes.

I bought the Sega brand VGA box directly from Sega when the DC was released back in Sept '99. A asked if the japanese version would work on a US system, and they told me no! When I received the VGA box from Sega, it was the Japanese version! LOL!!! (yes, CS isn't going to tell a consumer that it's ok to import).

1. Buy a generic DC VGA box
2. Open it
3. Disconnect (cut) wire connected to pin 6 on the DC connector
DONE

I was thinking of making my own because the 1st party ones are expensive, and I've heard some of the 3rd party ones are low quality, while some are just fine. Didn't feel like rolling the dice on a 3rd party one.

Also, they say that sometimes pins 6&7 are both tied to ground at the A/V plug, so you can't put a switch in the box to enable low res for Bangai-O, etc.

Using both H&V make sense, just curious about CSYNC. I assume it would need the same type of circuit.

[PC Engine Fan X!]

I bought a 1st party JPN Sega VGA Box off of eBay many moons ago and it works just fine on any DC console regardless of the region. Same could be said with 3rd-party produced ones as well.

PC Engine Fan X! ^_~

[SGGG2]

I have the clear one with the orange sticker that's all over sites like ebay and amazon, it's perfectly good. Haven't noticed a single bit of interference or anything odd.

[mesmer]

Cool, I guess 3rd party paranoia is just that.

[mesmer]

Why are there coupling caps on the RGB lines?

According to Viltim's site, PC VGA has DC offset video signals:
http://members.optusnet.com.au/eviltim/ ... ga2arc.htm

PC video (VGA, running special software)
Video amplitude: 0.7Vpp
Video DC offset: yes
Video input impedance: 75
separate horizontal and vertical sync
sync polarity changes (can be set in software)