Fw: MSX to VGA

[JP Grobler]

Hi
Sorry about the schematics going crazy. I typed them in Courier New - no
TAB's only spaces. I also added the schematics in gif format.
I saw there was some discussion on this topic, but it looks as if there
never was a defnite answer. There was a reference to Andre Delavy making a
RGB to SVGA connector does anybody know if he did? (Giovanni Nunes and
Fronteddu Stefano (later) made this reference) There was also a few comments
on the rgb to vga adapter by Novatec ( http://novatec-msx.da.ru/ )
Is looked at a few documents on the web and also at what the
amiga guys did. Not that I know muck about electronics - I can solder
circuits if I am told how, but that is basicaly it. (I do not quite follow
the circuits of the Novatec project but they do look great!)

This is what I found and concluded:

First: a RGB signal output is a must - most msx's have rgb output or
it can easily be added!
(see Hans Ottens home page - rgb on a svi-738(msx2 video
chip) http://www.geocities.com/msxhans/

Second: Both the vertical and horizontal sync must be seperated from the
composite sync.
True some monitors will accept composite sync in the
horisontal sync - but not all!!

http://www.hut.fi/Misc/Electronics/faq/vga2rgb/vgamonitor.html
A proposed seperator circuit is as follows, using a LM1881N
chip:(syncseperator.gif)

Here the Hsync is actualy still composite sync and must be
rectified still with the following circuit:
Schem2.gif

            +------------+---------- ---- Composite
            |            |  |---\
            | |---\      +--|    \
Composite --+-|    \        | AND |------ Hsync
              | AND |-------|    /
Vsync  -----+-|    /        |---/
            | |---/
            |
            +----------------------------Vsync

Using a chip like EL4583 will give you true hsync and
vsync and make all simpler.

Third: Connect Red, Green, Blue and Ground to the corrseponding vga
pins
(VGA 15pin : red = pin 1, green = pin 2, blue = pin 3,
ground = pin 5-8, 10, 11)

Fourth: Connecting the Hsync and Vsync
(Here I believe the trouble starts.) For the amiga I found
two different solutions:
1> Using a BC549 Transistor (Schem3.gif)
http://www.stud.uni-hannover.de/~andreash/com/a-vga.html
Amiga                BC549 (C B E)               VGA
                            | | |
5v -------------------------+ | |
                              | |
Hsync ------/\/\/\/\----------+ +-----------+--> Hsync
             100Ohm                         |
             +-----------/\/\/\/\/\---------+
             |            560Ohm
Ground ------+------------------------------> Ground
Vsync -----------------------------------------> Vsync

2> Using a 74HCT08 (used by commodore) or 74LS04 IC
low power TTL-level inverter)
+5v to the inverter chip with a 0.1 uF ceramic decoupling cap
between +5v and ground
Connect Hsync and Vsync via the IC to VGA
http://www.hut.fi/Misc/Electronics/faq/vga2rgb/vgamonitor.html

Hopefully this might work or help. I have not tried it yet but will as soon
as I get my hands on the components.

JP GROBLER
+27 11 957 3457 (tel/fax)
+27 82 293 2795
[EMAIL PROTECTED]

syncseparator.gif

schem2.gif

schem3.gif