22 Apr
2007
22 Apr
'07
9:40 p.m.
Hi,
A European PC with a CGA card will output 60Hz NTSC
video....
Whilst this is perfectly true, IIRC the IBM CGA monitor takes the "RGBI"
signal produced by the card, not the composite one.
I believe that the composite output was intended primarily for driving a
modulator to allow the use of an ordinary TV with the system.
Almost none of the "clone" CGA cards I've come across over the years support
the composite video output.
TTFN - Pete.
23 Apr
23 Apr
6:13 p.m.
Hi,
Indeed it does. And on an European PC, that RGBI signal is the same spec
as in the US version, that is, with 60Hz vertical sync frequency, etc.
It is possible to re-program the 6845 CRTC chip on the CGA card to get
50Hz vertical. I have a PAL encoder box that plugs into the DE9 connector
on a CGA card and which came with a little bit of software to do just
that. But no IBM machine did that as standard in the 'European' version.
A European PC with a CGA card will output 60Hz
NTSC video....
Whilst this is perfectly true, IIRC the IBM CGA monitor takes the "RGBI"
signal produced by the card, not the composite one.
I believe that the composite output was intended primarily for driving a
modulator to allow the use of an ordinary TV with the system.
The composite signal is output on 2 connectors on the IBM CGA card.
Firstly on the RCA phono socket on the back, indented to link to US TVs,
etc. And secondly on a 4 pin BERG header on the card. This was used to
connect the monitor in the 5155 PortablePC (the monitor in that is an
amber-screen Zneith composite mono monitor), and also to connect an RF
modulator (There's a 12V power output on another pin of that connector.
Almost none of the "clone" CGA cards I've come across over the years
support
the composite video output.
Odd. Just about all the ones I've seen did, although not necessarily on
an RCA phono conenctor on the bracket.
Some had that connector -- I have a clone CGA card which is pretty much a
copy of the IBM one apart from using different DRAM chips (I can't
rememebr if it's that they're 8 off 16K*1 5V-only ones, or a pair of
16K*4s).
I saw a clone CGA card _years_ ago which was one big ASIC and a couple of
RAMs. It had a 2-pin header plug on the PCB that carried composite NTSC
video. I never _owned_ that card though.
But I do have something called a 'Colorgraph+' It's a CGA card which can
take 48K of RAM (6 off 16K*4 chips), and thus has a 640*200 in 8 colours
(separate R,G,B bitplanes) mode, along with a 320*200 in 16 colours mode,
etc. This only has a DE9 connector, but pin 7, normally unused on a CGA
card, carries the composite NTSC signal.
-tony
24 Apr
24 Apr
5:42 a.m.
On Mon, 2007-04-23 at 23:13 +0100, Tony Duell wrote:
It's possible to program the CRTC on an EGA card to generate 640x400 at
15Hz and tweak an old CCTV monitor down to scan at that rate. Bloody
hideous to use for any length of time, but I was more impressed that I
got it to work. The two phono sockets break out to a header on the
board, so I birds-nested some resistors to generate a monochrome RGBI
signal and composite sync onto the pins.
Gordon
Hi,
Indeed it does. And on an European PC, that RGBI signal is the same spec
as in the US version, that is, with 60Hz vertical sync frequency, etc.
It is possible to re-program the 6845 CRTC chip on the CGA card to get
50Hz vertical. I have a PAL encoder box that plugs into the DE9 connector
on a CGA card and which came with a little bit of software to do just
that. But no IBM machine did that as standard in the 'European' version. A European PC with a CGA card will output 60Hz
NTSC video....
Whilst this is perfectly true, IIRC the IBM CGA monitor takes the "RGBI"
signal produced by the card, not the composite one.
6280
days inactive
6281
days old
2 comments
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participants (3)
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ard＠p850ug1.demon.co.uk -
classiccmp＠memory-alpha.org.uk -
gordon＠gjcp.net