Murugan wrote on 2020-05-06, 10:09:
As I found out, for some strange reason, my Olivetti monitor (according to the scarce info on the net) is EGA but only shows image when I hook it to the Olivetti that it came with.
On my IBM EGA and a EGA Wonder, only a scrambled line. My 5153 shows both an image when I confugure them for CGA.
Didn't know monitors could be picky.
Yeah, the monitors that came with the Olivetti M24 (as well as the AT&T 6300, which is exactly the same system sold under another brand) could work with *some* specific EGA cards, including the EGA Wonder 800 (not the 800 Plus, if I remember correctly). The STB Multires card might work as well.
It will not work with the original IBM EGA card, or on most other EGA clone cards.
The reason for this is because this monitor runs at 25kHz, as opposed to CGA (15kHz) and EGA (21.8KHz). This is because it supports 640x400 resolution on the M24, which was a proprietary mode introduced in that system.
EGA cards that support this proprietary signal type have a jumper for 25KHz mode. I believe the sync was also inverted or something. I can dig up some more info on that if you want.
I believe the Olivetti M240 (as opposed to the M24) also has a proprietary monitor with 640x400 support, but one that is downwards compatible with EGA at the software level. In contrast, the M24 only has CGA compatibility in addition to its proprietary 640x400 2-color mode.
You can find more about Olivetti monitors and their weird mode elsewhere in this forum.