BBC Micro to PC monitor?
David R
monitor?
Steven Bass
If so the answer is no for the following reasons:
1 The beeb scans at CGA frequency
2 The BEEB uses composite sync whilst the PC uses separate sync
3 The BEEB puts out TTL signal levels wheras the PC puts out analogue
signals.
If you had have meant an IBM CGA monitor then you would have stood a chance
by modifying the BEEB to produce separate sync signals and then tying the
intensite signal of the monitor either high or low (TTL logic levels). Mike
Cook (Micro User/Acorn User) showed how to do this some while ago.
Hope this helps.
Steve
Steve
David R wrote in message <784tf2$d...@jupiter.gre.ac.uk>...
Mark Davies
Steven Bass wrote:
> I presume by standard IBM PC monitor you mean VGA?
>
> If so the answer is no for the following reasons:
>
> 1 The beeb scans at CGA frequency
Don't forget that PCs are designed to be Backward compatible. Therefore you can
useCGA with a VGA monitor. ie:, you are using a 8086, or so, you can hook a VGA
up to it
no problem. You just cannot go the other way. That is of course if you have the
right vga
connector, 9 pin and 25 (???)
>
--
Mark Davies
IBM OS/2 Server for e-buisness
SUN Solaris 2.5.1
*No Winblows Sh#t here!*
Kira L. Brown
Mark Davies <Mar...@uunix.demon.co.uk> wrote:
>
>
> Steven Bass wrote:
>
> > I presume by standard IBM PC monitor you mean VGA?
> >
> > If so the answer is no for the following reasons:
> >
> > 1 The beeb scans at CGA frequency
>
> Don't forget that PCs are designed to be Backward compatible. Therefore you
> can use CGA with a VGA monitor.
No, you can't.
1) CGA is a digital standard, using TTL levels (0 and 5v.)
VGA, um, isn't, and doesn't.
This can be kludged using a few resistors, though.
2) VGA uses separate syncs, as does CGA. The BBC, being a TTL-level PAL
RGB signal, and not a CGA signal, uses composite syncs. *This* can
be kludged if necessary using a sync separator, but most monitors
don't seem to mind them mixed.
3) The BBC uses a fixed x-scan rate of 15kHz, and a fixed y-scan rate
of 50Hz. VGA (true VGA, not multisync) uses a fixed x-scan rate of
28800 Hz and a fixed y-scan rate of 60 Hz. These are not the same.
Most multisync monitors won't sync to y-scan rates of below 35kHz
anyway.
4) Even if it were a real CGA signal, which it isn't, it wouldn't work
with a VGA monitor becuase the x and y-scan rates would still be
out of band.
5) The backwards compatibility refers to graphics calls and to screen
modes- a VGA card is capable of generating VGA modes that look like
CGA modes to the software and to the human being at the other end
of the CRT. The signals, scanrates, and so forth, are totally
different.
kira.
--
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Roger W Wylde
<URL:mailto:Mar...@uunix.demon.co.uk> wrote:
>
>
> Steven Bass wrote:
>
> > I presume by standard IBM PC monitor you mean VGA?
> >
> > If so the answer is no for the following reasons:
> >
> > 1 The beeb scans at CGA frequency
>
> Don't forget that PCs are designed to be Backward compatible. Therefore you can
> up to it
> no problem. You just cannot go the other way. That is of course if you have the
> right vga
> connector, 9 pin and 25 (???)
Err I think you're confusing CGA emulation with the real thing,
PC graphics cards fake the low res CGA image onto a VGA display,
the Acorn GamesModes module does a similar thing for Arcs.
A standard VGA monitor will not sync down to the required
speeds to allow a beeb to use it, a multisync probably
would though.
And BTW unless you want to wire the monitor up to the printer
port I think you'll need 15 pins ;-).
Roger.
--
Roger Wylde - I.T. Technician, Droitwich Spa High School, Worcestershire
(Acorn Risc PC, 200Mhz StrongARM, 50Mb/1.2/6.4Gb and A4 Laptop, 4Mb/3Gb)
_____ _ ___ _____ _ _ mailto:ro...@nifty.demon.co.uk
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Mark Davies
Roger W Wylde wrote:
> > Don't forget that PCs are designed to be Backward compatible. Therefore you can
> > useCGA with a VGA monitor. ie:, you are using a 8086, or so, you can hook a VGA
> > up to it
> > no problem. You just cannot go the other way. That is of course if you have the
> > right vga
> > connector, 9 pin and 25 (???)
>
> Err I think you're confusing CGA emulation with the real thing,
I am sorry, yes I was talking about PCs.
> And BTW unless you want to wire the monitor up to the printer
> port I think you'll need 15 pins ;-).
>
Well, you *MAY* have noticed that I did put Bracketed Question Marks after that
statement,meaning I was taking a shot in the dark and could not remember the latter
VGA plugs.
> Roger.
>
> --
> Roger Wylde - I.T. Technician, Droitwich Spa High School, Worcestershire
> (Acorn Risc PC, 200Mhz StrongARM, 50Mb/1.2/6.4Gb and A4 Laptop, 4Mb/3Gb)
> _____ _ ___ _____ _ _ mailto:ro...@nifty.demon.co.uk
> | _ | | _|_ _| |_| | Visit the Nifty Web Site
> | | | | | |_ | | \ / url:http://www.nifty.demon.co.uk
> | | | | | _| | | | | Home of Nifty Software - lots of free software
> |_| |_|_|_| |_| |_| & Witley Court - Worcestershire's premier ruin
> -BBCs and Masters as well as other stuff, all for sale on the Nifty Site-
> - Comming Soon - NetGuard - Protect your networked Acorns -
--
Geoff Winkless
> 2) VGA uses separate syncs, as does CGA. The BBC, being a TTL-level PAL
> RGB signal, and not a CGA signal, uses composite syncs. *This* can
> be kludged if necessary using a sync separator, but most monitors
> don't seem to mind them mixed.
I'd say "some" - the cheaper ones tend to barf on composite sync.
> 3) The BBC uses a fixed x-scan rate of 15kHz, and a fixed y-scan rate
> of 50Hz. VGA (true VGA, not multisync) uses a fixed x-scan rate of
> 28800 Hz and a fixed y-scan rate of 60 Hz. These are not the same.
> Most multisync monitors won't sync to y-scan rates of below 35kHz
> anyway.
Uhh... what? Mine syncs happily at around 29k.
Geoff
(who hadn't even realised he bought a multisync when he bought it
second-hand as a '15" svga monitor' for £100 last year :)
David R
the BBC micro, and was asking for advice on behalf of a friend who
seems to think I know a bit about computers. Although your
suggestions sound technically fascinating, I simply do not have
the required time and knowledge to devote to such a complex
solution. (I was hoping there would simply be a BBC to VGA "black
box" out there for purchase.) Here's another thought: can the BBC
output a standard TV signal?
Kira L. Brown
Geoff Winkless <ge...@farmline.com> wrote:
> "Kira L. Brown" wrote:
> > 2) VGA uses separate syncs, as does CGA. The BBC, being a TTL-level PAL
> > RGB signal, and not a CGA signal, uses composite syncs. *This* can
> > be kludged if necessary using a sync separator, but most monitors
> > don't seem to mind them mixed.
>
> I'd say "some" - the cheaper ones tend to barf on composite sync.
Okay, but I don't buy cheap monitors :-) I buy expensive ones at
knocked down prices.
Any minute now Tom Rankin will be along to remind me about the three
VGAs in my spare room...
> > Most multisync monitors won't sync to y-scan rates of below 35kHz
> > anyway.
>
>
> Uhh... what? Mine syncs happily at around 29k.
Well, you have a monitor that syncs lower than most then. It still won't
sync to 15kHz, anyway.
> (who hadn't even realised he bought a multisync when he bought it
> second-hand as a '15" svga monitor' for £100 last year :)
Ah, they're all multisync these days. This old IBM thing, on the other
hand... *sizzle* *crack* *phut*... guess it doesn't multisync then :-)
Darren Salt
David R <D.Re...@gre.ac.uk> wrote:
[snip]
> Here's another thought: can the BBC output a standard TV signal?
Unless it's a Master Compact, yes.
--
| Darren Salt anti-UCE | ds@youmustbejoking,demon,co,uk | nr. Ashington,
| Risc PC, Spectrum +3, | ds@zap,uk,eu,org | Northumberland
| A3010, BBC Master 128 | arcsalt@spuddy,mew,co,uk | Toon Army
| Nothing much, coming your way *soon*,..
I have an inferiority complex, but it isn't a very good one.
Mark Usher
trying this out about a year ago.
>2) VGA uses separate syncs, as does CGA. The BBC, being a TTL-level PAL
> RGB signal, and not a CGA signal, uses composite syncs. *This* can
> be kludged if necessary using a sync separator, but most monitors
> don't seem to mind them mixed.
Yes indeed. I built a sync splitter according to Mike Cookes Body Build
artical and it split the two signals beautifully. You could always take them
directly off the 6845 chip though (pins 39 and 40), but as I was aiming to
make some sort of converter box....
>3) The BBC uses a fixed x-scan rate of 15kHz, and a fixed y-scan rate
> of 50Hz. VGA (true VGA, not multisync) uses a fixed x-scan rate of
> 28800 Hz and a fixed y-scan rate of 60 Hz. These are not the same.
> Most multisync monitors won't sync to y-scan rates of below 35kHz
> anyway.
Not quite.
The corect Hz rate is as follows for the PAL BBC.
625 lines
15.625khz Horiz Freq
50Hz Vert Freq
For CGA
15.75KHz Horiz Freq
60Hz Vertical Freq
The VGA stanadard is
31.5 KHz Horiz Freq
60Hz Vertical Freq
(28.000 MHz is the bandwidth)
>4) Even if it were a real CGA signal, which it isn't, it wouldn't work
> with a VGA monitor becuase the x and y-scan rates would still be
> out of band.
Well, as you can see VGA is for all intense and purposes double the Horiz
Freq of CGA and the BBC.
So I made a sync doubler. There are quite a few circuits knocking about the
internet for this as the Amiga happens to output also at this rate, and
there are rather alot of Amiga users who also want to connect up to a VGA.
In fact I use an Amiga monitor on my BBC :-)
Now back on topic. Running through the sync splitter on it's own I got a
perfect picture on a CGA monitor / EGA with TTL input.
Then adding the sync doubler I then connected up to a multiscan monitor. I
got vertically a rock steady picture. Unfortunately this was "ghosted"
horizontally. Since then I haven't made any more progress. If anyone wants a
copy of the sync doubler circuit then mail me and I'll send you a copy.
Mark Usher
BBC Documentation Project
http://members.magnet.at/marku/bbc.htm
Robin Clive-Matthews
<URL:mailto:D.Re...@gre.ac.uk> wrote:
> Thank you all for your advice. I'm afraid I don't know a lot about
> the BBC micro, and was asking for advice on behalf of a friend who
> seems to think I know a bit about computers. Although your
> suggestions sound technically fascinating, I simply do not have
> the required time and knowledge to devote to such a complex
> solution. (I was hoping there would simply be a BBC to VGA "black
Yup, should be via a phono socket on the back of the machine. It might need
retuning for compatability with Channel 5.
BFN !
--
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Tim Dean
> output a standard TV signal?
Yes
It is the phono connector next to the video out
ie between the bnc and the edge of the case
Tim
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Thomas Rankin
Kira L. Brown <kbr...@neutralino.demon.com.uk> wrote:
> In message <36A6F194...@farmline.com>
> Geoff Winkless <ge...@farmline.com> wrote:
>
> >
> > I'd say "some" - the cheaper ones tend to barf on composite sync.
>
> Okay, but I don't buy cheap monitors :-) I buy expensive ones at
> knocked down prices.
>
> Any minute now Tom Rankin will be along to remind me about the three
> VGAs in my spare room...
>
I wasn't going to say any such thing, I Wasn't even going to mention my spare
bi-scan CGA montior that has no problen with TTL signals or comp. sync.
You should have thrown some of those monitors out by now.
Besides, I've not been in your bedroom, you wouldn't let me near the flat.
Kira L. Brown
> Here's another thought: can the BBC output a standard TV signal?
Yes, it's on a socket on the back panel, phono type, marked 'UHF'.
It's tuned to about channel 36 so it may interfere with Channel 5
in your area. If so, you can take the lid off the Beeb and turn the
screw on top of the modulator.
Mark Usher
>Here's another thought: can the BBC
>output a standard TV signal?
A better picture can be obtained by connecting the BBC to a TV via the SCART
socket.
Details of how to make this cable are at
http://math.mmu.ac.uk/Physics/Acorn/BB/BB90.html