24 Apr
2007
24 Apr
'07
9:42 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.