RGB output to VGA monitor, is it possible?
S R Cumpson
I have an old VGA monitor which I would like to use with an even older
computer that has an RGB output, composite output and RF output.
I would preferably like to use the RGB connector if I can.
As I understand RGB uses a series of TTL digital signals whereas VGA
is analogue, what I would like to know is, can anyone help me with
some ideas of how I could proceed ? Does anyone know of a circuit that
could do what I want?
I don't mind experimenting with circuits if anyone has any suggestions.
Cheers
--
Stephen Cumpson email:mbh...@afs.mcc.ac.uk
Information Storage Research Group
University of Manchester, UK
M13 9PL Tel.: 0161 275 4532
Samuel M. Goldwasser
>Hi
>
>I have an old VGA monitor which I would like to use with an even older
>computer that has an RGB output, composite output and RF output.
>I would preferably like to use the RGB connector if I can.
>
>As I understand RGB uses a series of TTL digital signals whereas VGA
>is analogue, what I would like to know is, can anyone help me with
>some ideas of how I could proceed ? Does anyone know of a circuit that
>could do what I want?
It is not only the signals:
If your VGA monitor is strictly VGA - 31.4 KHz - then its scan rate
is incompatible with what is most likely CGA on your computer. Changing
scan rates is not something that you want to do.
If the monitor is multisync and goes down to the 15KHz range, then
a conversion is possible. Mono/CGA/EGA use TTL signals. VGA is .7
V p-p analog for each of R,G,B.
VGA cards are so cheap now that it may pay to just buy one - probably
under $30 (except that if your computer is an XT, it only has an 8 bit
bus and VGA cards are nearly always 16 bit).
--- sam
A.R. Duell
>S R Cumpson <mbh...@afs.mcc.ac.uk> wrote:
>>Hi
>>
>>I have an old VGA monitor which I would like to use with an even older
>>computer that has an RGB output, composite output and RF output.
>>I would preferably like to use the RGB connector if I can.
>>
>>As I understand RGB uses a series of TTL digital signals whereas VGA
>>is analogue, what I would like to know is, can anyone help me with
>>some ideas of how I could proceed ? Does anyone know of a circuit that
>>could do what I want?
I really wish people would stop using 'RGB' to mean TTL-level RGB. All
RGB means (when applied to monitors, computers or whatever) is that the 3
colour signals are available separately, and not encoded as PAL, NTSC, or
whatever
>It is not only the signals:
>If your VGA monitor is strictly VGA - 31.4 KHz - then its scan rate
>is incompatible with what is most likely CGA on your computer. Changing
>scan rates is not something that you want to do.
It could be almost _any_ scan rates. UK TV rates (15625Hz horizontal,
50Hz vertical), EGA rates, MDA rates, but colour (the FTS series 88 used
these), etc. That, as you say, is the biggest problem. Signal conversions
are next-to-trivial :-)
>VGA cards are so cheap now that it may pay to just buy one - probably
>under $30 (except that if your computer is an XT, it only has an 8 bit
>bus and VGA cards are nearly always 16 bit).
Please don't assume computer = PC. I could easily name 10 machines, all
sold quite widely in the UK with RGB outputs (TTL, analogue, or
whatever) which certainly couldn't take a VGA card (or any other PC-bus
card).
>--- sam
-tony
Samuel M. Goldwasser
>I really wish people would stop using 'RGB' to mean TTL-level RGB. All
>RGB means (when applied to monitors, computers or whatever) is that the 3
>colour signals are available separately, and not encoded as PAL, NTSC, or
>whatever
True enough.
>>It is not only the signals:
>
>>If your VGA monitor is strictly VGA - 31.4 KHz - then its scan rate
>>is incompatible with what is most likely CGA on your computer. Changing
>>scan rates is not something that you want to do.
>
>It could be almost _any_ scan rates. UK TV rates (15625Hz horizontal,
>50Hz vertical), EGA rates, MDA rates, but colour (the FTS series 88 used
>these), etc. That, as you say, is the biggest problem. Signal conversions
>are next-to-trivial :-)
>>VGA cards are so cheap now that it may pay to just buy one - probably
>>under $30 (except that if your computer is an XT, it only has an 8 bit
>>bus and VGA cards are nearly always 16 bit).
>
>Please don't assume computer = PC. I could easily name 10 machines, all
>sold quite widely in the UK with RGB outputs (TTL, analogue, or
>whatever) which certainly couldn't take a VGA card (or any other PC-bus
>card).
I guess I am a bit PC-centric. In fact, from email it is clear that
what he has is not a PC. However, an RF output would most likely
imply an NTSC or PAL output which makes the remainder of these comments
probably valid - the scan rate is the key.
--- sam
Hermann Reese, Mexico-City
Most older VGA-Monitors have Hor. scan rates around 15kHZ and 50
or 60HZ Vert. scan rate. A pinout diagram of your monitors input
would be very helpful. Try to find out if it has different inputs
for analogue or TTL RGB. TTL-RGB requires separate Sync Inputs
for Hor/Vert Sync. If your computers output provides these Sync
signals you would have to connect minimum 5 signals (R,G,B,
H/V-Sync and Ground). Some analogue RGB systems provide Sync on
Green, so you may have a picture just connecting the Green
channel and Ground. Once you figure out which signals are on what
pins you may try various connections and see how the monitor
reacts. Its OK to experiment with the signal connections. No harm
can be done as long as you don't short circuit any of the
computer outputs to ground or against another signal output.
Hope this helps somewhat.
Regards
Hermann
-Hermann Reese
-CompuServe 74052,610
Samuel M. Goldwasser
>Stephen.
>Most older VGA-Monitors have Hor. scan rates around 15kHZ and 50
Actually, if the monitor is called a VGA monitor, it likely is fixed
frequency at 31.4KHz.
I agree that older multisync mointors have inputs for VGA, EGA, even
NTSC. The Mitsubishi AUM1381 is one example of such a monitor (quite
nice for its day - I still use one on one of my PCs.). The pinout
may be non-standard for the VGA, however, as suggested below.
Unless the monitor is clearly marked, it would really be helpful to
find out ahead of time what the specs and pinouts are - there may be
too many permutations.
>or 60HZ Vert. scan rate. A pinout diagram of your monitors input
>would be very helpful. Try to find out if it has different inputs
>for analogue or TTL RGB. TTL-RGB requires separate Sync Inputs
>for Hor/Vert Sync. If your computers output provides these Sync
>signals you would have to connect minimum 5 signals (R,G,B,
>H/V-Sync and Ground). Some analogue RGB systems provide Sync on
>Green, so you may have a picture just connecting the Green
>channel and Ground. Once you figure out which signals are on what
>pins you may try various connections and see how the monitor
>reacts. Its OK to experiment with the signal connections. No harm
>can be done as long as you don't short circuit any of the
This is usually the case but there are no guarantees - some (poorly
designed) monitors may self destruct if fed no sync or improper sync.
--- sam