Yes, Bunsen, that was the thread to which I was referring, thanks!
I think the adapter takes the Compact Mac video signal and converts it to TTL, which it then adapts to EGA. You both say it is not an EGA standard, but if the purpose of the adapter circuitry is to generate the extra scan lines to blank the top and bottom of the image to match EGA 640x350, wouldn't that then match the standard? Can the miniscule .4 difference between 21.8 and 22.3 kHz really make them entirely incompatible?
Not that it would be impossible, but why make an adapter that could only drive custom Mac displays, designed for just this adapter? Look at the old Power R site and you'll notice the Color Classic adapter manages to offer a VGA signal at 512x384 and 25.5 kHz, which also does not match VGA specs, so it must do something similar.
Thanks for the other link, I think reducing the VGA signal to lower scan rate is far easier than going the other-way, as evidenced by the numerous and inexpensive VGA to EGA cables to convert a VGA signal for use on an EGA monitor. The hard part is making it compatible with the compact Mac CRT. I found numerous LCD panels that are designed for legacy equipment and accommodate CGA, EGA & VGA, etc. input, but they are quite expensive. I also found a less expensive but still costly CGA to VGA converter and wondered why not an EGA version. Weren't CGA & EGA compatible?
UPDATE: Looking at the actual adapter, of which I shall post some pics, there are only 4 wires coming out of it and into the DE-9 cable. So what is that? H, V, G & monochrome signal split to the RGB pins?
I think the adapter takes the Compact Mac video signal and converts it to TTL, which it then adapts to EGA. You both say it is not an EGA standard, but if the purpose of the adapter circuitry is to generate the extra scan lines to blank the top and bottom of the image to match EGA 640x350, wouldn't that then match the standard? Can the miniscule .4 difference between 21.8 and 22.3 kHz really make them entirely incompatible?
Not that it would be impossible, but why make an adapter that could only drive custom Mac displays, designed for just this adapter? Look at the old Power R site and you'll notice the Color Classic adapter manages to offer a VGA signal at 512x384 and 25.5 kHz, which also does not match VGA specs, so it must do something similar.
Thanks for the other link, I think reducing the VGA signal to lower scan rate is far easier than going the other-way, as evidenced by the numerous and inexpensive VGA to EGA cables to convert a VGA signal for use on an EGA monitor. The hard part is making it compatible with the compact Mac CRT. I found numerous LCD panels that are designed for legacy equipment and accommodate CGA, EGA & VGA, etc. input, but they are quite expensive. I also found a less expensive but still costly CGA to VGA converter and wondered why not an EGA version. Weren't CGA & EGA compatible?
UPDATE: Looking at the actual adapter, of which I shall post some pics, there are only 4 wires coming out of it and into the DE-9 cable. So what is that? H, V, G & monochrome signal split to the RGB pins?