Re: What is the status of a C128 or c64 to VGA interface...
- From: "Wildstar" <wildstar128@xxxxxxxxxxx>
- Date: Sat, 3 Nov 2007 17:31:43 -0700
There is truth in the matters of the board in the RGBI monitors. Have you
ever looked at the schematics of a 1902A monitor. Wouldn't you think that
will solve part of the matter because VGA monitors are 31KHz Analog RGB
monitors. Always has and always was.
Is that clear? I am suggesting an option that can work with some little bit
of work. You do realize the VDC "R,G,B,I" pins are nothing more than digital
bits that are converted to analog R,G,B signals for controlling the signal
intensity of each of the R,G,B raster guns. Basically the raster guns
convert voltage signals to light. It is like having three light bulbs with a
red, green, blue plastic filter and a variable setting light switch. You
can get where they got the idea from a classic experiment you see in a
Physics class.
More digital bits, more color. Why do you think the 1902A is called a
digital RGB monitor. The truth is, the CRT is analog like any other CRT. It
is the DAC board that makes the difference. The key is what form of signals
it accepts. Amiga does this onboard - hence analog output. There is no
particular reason - what I said can't work. At least the theory. It is
general enough to be worked out. If I had the equipment and the time and
sufficient knowledge of where to solder a wire and what editional components
that I need for memory buffering and how to wire that. That is the technical
details that I don't have the skill in. I am pretty confident that it is
possible with someone who knows how to properly wire several
transistors/capacitors, resistors, ect. sufficient to know blow the circuit
and destroy components. I am however have a little idea of what to do and
with the time, I would be able to make it work. I do have electronics books
and read them in the past but haven't practice with basic electronics in
recent times to remember everything. When you on rare occassions dabble with
something, you don't remember all the details.
I am familiar with the fact that you need to put in a scanline doubler to
make it work with a VGA monitor. The number of colors part is merely
mathematics and the trick is finding distinct states of color and at a
point, there would be no way to distinquish between one color and the next
color at such resolution as 48-BIT color (16-BIT Red, 16-BIT Green, 16-Bit
Blue.) That doesn't matter and having access to more color is merely going
to be based on tuning the number of shades of each of the Red,Green and Blue
raster gun and what intensity settings for each raster gun beam.
The color you see on-screen is based on these three raster beams projecting
to the same point on the screen (pixel / picture element). With RGB, each
picture element is formed by the three raster guns projecting light at the
same point (or area of proximity too closely placed together that the human
eye does not distinques each of the r,g,b elements forming the pixel)
You know it. I know it. That is what a CGA/VGA/VDC chip does. Sends the
signals needed to set these raster guns. There really is no distinct number
of settings. Like there is no limit of how many settings you can have in a
variable switch for you incandescent light bulb.
The limit is in the switch. The DAC board, + number of input lines to the
DAC board and the output side of the DAC board is the limit. The DAC board
is the key point of interest. Not the VDC or the CGA card. It helps but not
the only way to overcome color limitation. It wouldn't matter what your
video card is if the monitor can't display more color. That is why we went
to analog monitor so all someone had to do is replace the video card. The
video card then contained the DAC not the monitor.
"Klompmeester" <whowhere@xxxxxxxxxx> wrote in message
news:13iq2dolr6mst36@xxxxxxxxxxxxxxxxxxxxx
"Wildstar" <wildstar128@xxxxxxxxxxx> wrote in message
news:EYRWi.114$n75.34@xxxxxxxxxxxxxxx
Another funny thing is there is a half the hardware you need for 128 to
VGA converter built in the 1902A monitor. This is a DAC board in the
monitor like all CGA monitors have.
First off, the CGA or C128 VDC video output is actually digital. The RGB
values are merely bits. What happens is that when the video bits are
being sent to the 1902A monitor ( and most other CGA monitors ) is the
signal is then converted from bits to analog R,G,and B and I video
signals.
So why do I say that this is half of what you need. You'll need to supply
power to it if you take it out of the monitor. (Basically, steal this
little board out of the monitor) You also need to build a scanline
doubler which would be to convert the analog R,G,B signals running at 15
KHz scan rate to 31 KHz scan rate just like the Amiga. The Analog R,G,B
signals are in all respect, the same as the analog R,G,B on the Amiga.
Without this card in a 1902A monitor, the 1902A would be nothing more
than an analog RGB monitor like the Amiga RGBs (pre-VGA like the
A1000,A500,A2000).
So in reality, you mainly need is a scan-doubler. There maybe some other
components for stabilization and quality of video signal. All CGA
monitors contains this basic circuit with varying output results.
THEORY:
With additional data lines and components and replacing of the "4bit
digital input (R,G,B,I) to 4 Bit resolution R,G and B" DAC to 4bit DACs
for each of the R,G,B and I lines with 16-BIT analog RGB output. However,
you would need to pipe in additional data lines (although with
limitations*) to supplement the colors. You would also need some sort of
buffer to remember the extra data signals.
Limitations would be that you would only be able to provide the
additional 12 Bits at data rate of the CIA not the dot clock rate. Thus,
you would not be able to have the 16 colors at a time per character cell
or two at a time at best. Since only 4 bits would be sent at full speed.
So you would typically use the slower 12 Bits as a palette switch. Like a
bank switch mechanism. Which you would only change at a slower rate.
Right off the bat, these are something that would be apparent and
obvious. Since the C-128 has no other data lines operating at the rate
that the normal VDC's RGBI "data lines" operates at. You would have to
have some sort of memory mechanism for remember the 12 bits that are are
fed in from other sources. It is most likely that you will have to have 8
bits to supplement the 4 bits from the VDC and only get 12-BIT (4096
colors with only 16 colors at a time). Another option is two use a two
stage palette switching mechanism. 8 bits from User Port, 4 bits from say
the Joystick port or another port and the 4 bits from the VDC.
However, this is basic theory. So far, we been testing this theory out
with typical CGA to VGA converter chip not with very basic and
straightforward TTL DACs which would be more flexible in my opinion. In
fact, it would be more flexible because we can outright make the circuit
to what we want at component level since some of these pre-built chip
solutions are "hard-wired" a certain way and there is little to no
option. At the same time, we can proof-test this at 15 KHz and see it
functional on an actual CGA / 1902A monitor since the analog side should
have really no limit of color like the analog RGB monitors on the Amiga.
Since we don't need to scanline double until later. The CRT should be
able to display an unlimited number of colors. This very board in the
monitor is the "governor" on terms of color output. Mechanically, there
can be and should be no limit on color. Each of the Red,Green and Blue
raster guns should be able to send out virtually as many shades of
red,green and blue that you can set a setting for. In theory, you can
have a 16-BIT DAC resolution for each of the Red, Green and Blue raster
gun. Imagine 65536 shades of Red. 65536 shades of Green and 65536 shades
of Blue. For a total of 65536 x 65536 x 65536 colors. 281,474,976,710,656
colors ???? Ok, we don't need that many. At the same time, there is
likely little to any chance of getting a clean 65536 states for each of
the R,G and B raster gun.
The C128 also doesn't have sufficient data lines. A modern PC would have
the speed to be able to sufficiently supply enough data lines at
sufficient speed to match the clock rate of a CGA or VDC card.
Do you just make this stuff up as you go along or what?
.
- References:
- Re: What is the status of a C128 or c64 to VGA interface...
- From: Wildstar
- Re: What is the status of a C128 or c64 to VGA interface...
- From: Klompmeester
- Re: What is the status of a C128 or c64 to VGA interface...
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