68kMLA Classic Interface
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| EGA out on compact macs | |
| Posted by: WhoaMan on 2011-11-19 20:58:33 Recently, I got a Mac Plus board from a member of these forums for a project that I am working on. I am not far enough in this project to where I need the board, but figured it would be nice to have on hand for when I am ready... and decided to play around with it in the meantime. Since I just have the logic board, I decided to hook it up to a CGA EGA monitor. Anyways... here are the results:  Normal, low intensity green. In Amber Monochrome mode I also have a nice new wallpaper! Here is a quick schematic, it uses a 74ls04 hex interter, 4 SPST switches to adjust the foreground color (BG is black), and two SPDT switches for both the H Sync select and Video select. | |
| Posted by: johnklos on 2011-11-19 23:59:37 Are you sure that's not an EGA monitor? CGA is 15 kHz and compact Macs put out 22.3 kHz, if I remember correctly. EGA is 21.8 kHz, which is close enough that it should work, but I can't picture CGA reaching that far without some tweaking. | |
| Posted by: zuiko21 on 2011-11-20 02:00:56 I think it should be EGA, too -- ot maybe that's an old multi-scan monitor? CGA has 200 lines only, while EGA has 350 -- very close to the Compact's 342, so it's very likely to work OK. Anyway, it's a very interesting work! I see that you can choose between straight and inverted signals for H-sync and Video... which are the 'proper' settings? Maybe you'd like to use a couple of your unused inverters in series for the "straight" video connection -- just in order not to overload the Mac's output in case someone likes to get a bright white image (the four inputs in parallel!) Thanks for sharing! | |
| Posted by: Bunsen on 2011-11-20 20:30:00 WhoahMan, nice work indeed! Yes please do clarify for those asking in regards to CGA vs EGA 🙂 | |
| Posted by: bigmessowires on 2011-11-20 21:17:18 That's pretty cool! What have you got planned next? | |
| Posted by: WhoaMan on 2011-11-20 21:28:37 I apologise, the monitor is actually an EGA monitor and is running in EGA mode due to the negative vsync. I do have to admit, I am curious as to what would happen if i inverted vsync and tried it in CGA mode, maybe I will have to try that out sometime tomorrow on both this monitor and another that is strictly CGA. | |
| Posted by: WhoaMan on 2011-11-20 21:33:39 zuiko21, most people would want to use set sw-hselect and sw-vselect to use the outputs from the 7404. The only reason i added the ability to switch between /hsync and hsync has to do with a few arcade "CGA" monitors that I have sitting around... just in case i decided to hook it up to a bigger screen 😉 . | |
| Posted by: Bunsen on 2011-11-23 16:27:34 Title fixed 🙂 Really wishing I hadn't ditched my 23" EGA CRT now :/ | |
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