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                     Videogames on Alternative Monitors FAQ
                               Jonathan Dawes              

                          Last Updated: 12th Nov. 96

This FAQ is an attempt to provide answers to all those who, like me, have
tried to attach their video games to either TVs or VGA monitors. It covers
VGA monitors, SCART TVs, and RGB to composite video/UHF.

Thanks to John Keay <keay@tiuk.ti.com> for the SCART and 1084 pinouts

If you have any comments please feel free to mail me at
<jond@videologic.com>

Disclaimer
----------

This document is provided for informational purposes only.  While every 
effort has been made to ensure its accuracy, neither the author nor any
contributors can guarantee the accuracy of the information herein, and 
cannot be held responsible for anything arising as a result of activities
using the information provided in this document.

The opinions expressed herein are not necessarily the opinions of
the author's employers.

------------------------------------------------------------------------

Section 1)  VGA Computer Monitors

I should point out right away that this doesn't contain instructions because
there is no way it can be done.  Here's the deal:

Video games, on the whole, use a 15 Khz horizontal sync, which means they 
display a line 15000 times a second.  VGA monitors use 35 kHz, which
means they display 35000 lines per second. This means that your VGA monitor
will try to draw two lines with the picture data from one game line.  It 
simply won't work.  Often the monitor will manage to sync horizontally, but
the lines will look scrambled and the picture will roll vertically.

So, what about these Multisync monitors?  Well, old EGA used to use 15kHz
line rate, but it was digital input only and games use analogue video.  
However, older mutlisync monitors like the NEC 3D could do both analogue VGA
and digital EGA, and as a result they were able to sync down to 15kHz, 
regardless of whether the picture input was analogue or digital.

Since EGA is now dead and buried, modern monitors don't support 15kHz
line rate.  Modern multisync monitors in fact go the other way.  They are
capable of syncing *up* to much higher line rates, and down only to about
31.5 kHz.  So, no matter how snazzy a monitor you have, if it's new
the chances are very slim indeed that it will work with your video games.

Commodore 1084 monitors apparently work due to the fact that Commodore 
machines had modes that ran at 15KHz line rate.
The pinout for the Commodore 1084 is below, courtesy of John Keay.  You use
this information at your own risk.


 -----------  Pin out (looking into connector from the outside I guess) 
 \1 2 3 4 5/
  \6 7 8 9/
   -------
     
1 Ground
2 Ground
3 Red
4 Green
5 Blue
6 Intensity
7 N/C
8 Horizontal sync
9 Vertical sync
     
You shouldn't need to connect pin 6 (or 7).
     
If the game has combined h/vsync (ie a Csync like all JAMMA boards) then 
connect it to pin 8 (HSYNC) and leave pin 9 unconnected.


As I said before, the NEC 3D  works, just feed in the RGB and your manual
should describe how to feed in composite sync.


Section 2)  Televisions (SCART, Composite Video)

There have been many posts on rgvac along the lines of:
"How do I connect up my game to my TV?"

This can be accomplished in a number of ways:

1)  SCART TV

This is by far the easiest way to get your game boards working on a TV
and gives the best picture.  European TVs often come with a SCART or
Euro-connector as standard, which has RGB and composite 15kHz sync
inputs.  5 wires are all you need for this. Simply connect the RGB
out from your game to the RGB in on the socket (buy a plug, it's a 
*lot* easier than poking wires in the socket). Next, connect the video
ground to the RGB grounds, and connect the composite sync output
to Composite Video In on the SCART socket.  This last stage is because
the TV doesn't care which channel it gets its sync from, RGB or composite
video, it all goes to the same circuit.

On some TVs you must tie the blanking pin low, but for most this will
work straight away.  And that's it.  Just select the correct channel
on your TV for SCART input.  You can also feed the sound in through 
the SCART port, but be careful not to turn the volume up on your game
board, you could damage the TV.  Keep it low, and it should be fine.

Here is the pinout for a SCART plug, courtesy of John Keay.  Again, you 
use this information at your own risk.
     
                       +---------+
    Audio Output B     |  1      |
                       |      2  | Audio Input B
    Audio Output A     |  3      |
                       |      4  | Audio GND
    Blue GND           |  5      |
                       |      6  | Audio Input A
    Blue               |  7      |
                       |      8  | Function switching
    Green GND          |  9      |
                       |      10 | Communication data line 2
    Green              |  11     |
                       |      12 | Communication data line 2
    Red GND            |  13     |
                       |      14 | Communication data GND
    Red                |  15     |
                       |      16 | Blanking
    COMP video GND     |  17     |
                       |      18 | Blanking GND
    COMP video output  |  19     |
                       |      20 | COMP video input 
    Common GND         +--21-+   |
                              \  |
                               \ |
                                \|
     
     
Game                 TV
Board          Pin name   pin number(s)        
-----        ----------------------- 
Red            Red          15
Green          Green        11
Blue           Blue          7
GND            Grounds       5, 9, 13, 18, 21 
SYNC           Video input  20
+5             Blanking     16
     
The RGB inputs are active high (i.e. "standard" RGB levels) and the 
SYNC signal needs to be an active low combined vertical and 
horizontal sync (i.e. a JAMMA-like SYNC).
     
The only problems I had were when I didn't connect the blanking 
pin (the picture synced up but everything was nearly black).

Pins 8 and 16 on a SCART port as supposed to be used to select different 
kinds of source signals (UHF, RGB or Composite video), my TV didn't
seem to care so I left them unconnected, but here is the coding 
table just incase.
     
Pin 8  Pin 16
   0      0   UHF
   0      1   RGB
   1      0   Composite video
   1      1   RGB



2)  RGB to NTSC/PAL converters.

This isn't as complex as it sounds.  Several chips exists to do this
conversion, and require only a crystal, and some termination resistors.
However, it should be noted that unless you are willing to pay for the
more expensive chips, the picture isn't that great, sort of like a 
cheap video camera image.

Analog Devices' AD720 chip is the most expensive, but will give very good
results.  It is a little under 20 UK pounds.

Sony do three cheaper chips, each one with a different price, and different 
picture quality.  I tried the 1645 which is about 6 UK pounds.

Instructions can, I believe, be found on the packaging, but suffice to say
that you connect up the crystal or clock source to the pins indicated, 
terminate the RGB into 75 Ohms to ground, and feed them into the RG and B
inputs on the chip, along with the composite sync in.

The composite video out can then be taken and fed into your TV or video.
For those with S-Video equipment, the chips also output seperate luma and 
chroma so you can get an improvement in picture quality by not having to 
combine them.

3)  Composite Video To UHF Modulators.

This composite signal can be fed into a modulator, a single stand alone
module that turns the video signal into a TV signal.  Aztec make a pretty
good one, but if I remember, they're not cheap.  Picture quality is pretty
good, most of the loss comes from the RGB-NTSC/PAL conversion

The Composite Video should be terminated into a 75 Ohm resistor to ground
then for best results fed into a 10MHz low pass filter before going into 
the modulator.  Then just supply power, and take the output into the 
aerial socket on your TV. 

 


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