Newsgroup: it.comp.retrocomputing
Titolo: C128: Conversione da RGB digitale a RGB analogico

Sapete se è possibile convertire l'uscita video RGB-I del Commodore 128 in modo che possa essere collegata all'ingresso RGB analogico dei monitor Commodore 1084S-D2, Amiga (Microvitec) M1438S, o di un televisore dotato di presa SCART?
Ho fatto delle ricerche con Google, ma finora non ho trovato nulla! :-(
Gustav

 Sapete se č possibile convertire l'uscita video RGB-I del Commodore 128 in
modo che possa essere collegata all'ingresso RGB analogico dei monitor
Commodore 1084S-D2, Amiga (Microvitec) M1438S, o di un televisore dotato di
presa SCART?
Il monitor 1084S accetta i due segnali. Dietro dovrebbe avere un pulsante
per la scelta del tipo di segnale RGB analogico/RGB digitale.
--
ZaXxon

Ho fatto delle ricerche con Google, ma finora non ho trovato nulla! :-(
Qui di seguito un post che ho raccolto da qualche parte. Non so se
funzioni ma con un C128 che comperai mi diedero pure un cavo 80
colonne-scart
----------------------------------------------------------------
I just hooked my C128 to my 15" television set. The same cable can be
used
for both 40 and 80 column screen, as I have a switch in it.
This cable is based on an article in C=Lehti 2/89. It had some
inaccuracies,
and it is in Finnish. So I'll describe the cable here.
The RGBI connector looks like following, when looking to the machine's
rear
side from outside:
	5   4   3   2   1
	  9   8   7   6
(The User's guide and the C=Lehti article used the mirror image of this,
which confused at least me.)
The pins are as follows:
	1 GND	ground
	2 GND	ground
	3 R	red
	4 G	green
	5 B	blue
	6 I	intensity
	7 VIDEO	composite video
	8 HSYNC	horizontal sync
	9 VSYNC	vertical sync
My television has a 21-pin Scart connector, which is used in Europe. It
is
a special type of connector that has rectangular plates as pins. The
pins
are surrounded by a pentagonal metal frame. It looks like the following:
	_________________________________________
	|                                       |
	| 1   3   5   7   9  11  13  15  17  19 |
	|                                       |
	|                                        \
	|   2   4   6   8  10  12  14  16  18  20 \
	--------------------------------------------
The needed pins are:
	4, 5, 9, 13, 17	ground
	2		audio, right channel
	6		audio, left channel
	7		blue
	11		green
	15		red
	20		video
	16		fast blank
The Scart connector does not allow use of HSYNC and VSYNC signals, so it
uses a video signal to synchronize the RGB picture. As the video signal
can be used also without RGB, the "fast blank" signal is needed to
enable
RGB signal, unless you have a switch in your television to enable RGB.
When the television or monitor gets a positive voltage to the "fast
blank" pin,
RGB will be enabled. The C=lehti article instructed to tie VSYNC to this
pin through a 220 ohm resistor to provide the voltage, but it was too
weak for
my TV. So I temporarily used a 9 V battery to get some color on the
screen.
Finally I hooked that pin to the cassette port's +5V output.
The television expects analog RGB, but the C128 outputs digital RGB. The
signals can be converted to analog using six resistors:
digital              analog
	R ---- R1 ---- R ---- R4 ---+
                                    |
	G ---- R2 ---- G ---- R5 ---+
                                    |
	B ---- R3 ---- B ---- R6 ---+
                                    |
	I --------------------------+
The article suggested R1, R2 and R3 to be 470 ohms and R4, R5 and R6 to
be
680 ohms. You can experiment with other values to get good-looking
colors
on the screen.
On some C128's, the RGBI connector's VIDEO signal might be actually 40
column
screen's video signal, or the C=Lehti article is simply wrong when
claiming
that you can get the 40 column screen via the RGBI connector. In any
case,
you get sound and 40 column screen from the 8-pin VIDEO connector. You
can
plug a 180 degree 5-pin DIN connector to it. The pin 2 is ground, 4 is
video
signal and 3 is audio output.
Finally you have to add a 2*ON-ON switch to switch between 8563 and 8566
screen. Connect it as follows:
                       /
  RGBI Video (7)-----o/  80 column screen
                     /|
Scart Video (20)----/ |
                      |
   VIC Video (4)-----o|  40 column screen
                      |/
  voltage supply-----o/
                     /
 Fast blank (16)-R7-/    R7=220 ohms
                     o
As mentioned above, you might be able to use VSYNC as voltage supply. If
the cassette port's +5V pin is not enough for your TV or monitor, use a
9 V battery or take a +9V or +12V lead from your computer.
Be careful with the 80 column mode. If you reset the computer to 64
mode,
the VDC screen will be out of syncronization, and your monitor may start
to smoke if you leave the cable in 80 column mode for several seconds.
Part list:
	Quantity	Quality
	========	=======
	   3		470 ohm resistors
	   3		680 ohm resistors
	   1		220 ohm resistor
	   1		Scart connector
	   1		D9S connector
	   1		5-pin 180-degree DIN plug
	   1		2*ON-ON switch
To connect your C128's 80 column screen to a CGA monitor, simply connect
all
wires.
Have fun connecting!
	Marko Mäkelä


omissis

 per la scelta del tipo di segnale RGB analogico/RGB digitale.
Purtroppo il modello in mio possesso non ha l'ingresso RGB digitale.
E' infatti il "D2", l'ultima incarnazione del 1084S, prodotto dalla Daewoo.
Comunque ho trovato gli schemi per convertire il segnale da digitale ad analogico.
Ciao
Gustav

Mauro Raucci e/o Mena di Grazia, on 26-Dic-02 13:00:23 you wrote:   
 MRe> Ho anch'io questo problema, e conosco questo sito, ma i diagrammi che
 MRe> mostra non sono chiari per un neofita dell'elettronica come me.
Prova questo:
http://home.t-online.de/home/Birger.Hahn/hardware/c128_rgbi_am_tv.htm
Ciao!
Gustav


ciao,
prova anche questo circuito:
http://emulazione.multiplayer.it/cbmitapages/tecnico/128vout.jpg
Spero che non sia troppo complicato.
Alle prox!
Griphon.