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Post by oziphantom on Nov 27, 2019 10:29:43 GMT
I think it comes down to front porch, back porch, timings and voltages as well as just running at 60hz.
your scandoubler is FPGA right? that shouldn't have issues with a 16mhz pixel clock.
@mybombermillzy well the beagleboard would have a frame buffer internally, in that it uses the 200mhz PRUs to capture the RGBI values, then plots them on the frame buffer which then goes out to HDMI. And you could draw sprites etc on the top.
Martin Piper is making a graphics expansion board that is based upon the BombJack arcade, which uses RGBI values. So one could easily blend it with the VDCs output, just take the RGBI & it all together, invert it and put it to a mux to select the VDC or Expansion graphics.
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Post by oziphantom on Nov 27, 2019 10:39:16 GMT
Rather than photos which are very hard to get, the game one does basically look like that in real life but here are the prgs
Has anybody done any experiments with faster refresh rates and the 1084s.. the above put it into NTSC 60hz mode. But if we start cutting down the number of rows, vblank time etc can we start push it up to 70hz??
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Post by remark on Nov 27, 2019 15:50:45 GMT
Rather than photos which are very hard to get, the game one does basically look like that in real life but here are the prgs
Colour Gradiants : Game Test :
Has anybody done any experiments with faster refresh rates and the 1084s.. the above put it into NTSC 60hz mode. But if we start cutting down the number of rows, vblank time etc can we start push it up to 70hz??
On my PAL 1084 monitor (mono version) the image flickers in both programs.
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Post by oziphantom on Nov 27, 2019 16:05:08 GMT
yes they are interlaced mode. 640x400 but its still chars so 80x50 mode.
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Post by mrbombermillzy on Nov 27, 2019 20:14:46 GMT
Has anybody done any experiments with faster refresh rates and the 1084s.. the above put it into NTSC 60hz mode. But if we start cutting down the number of rows, vblank time etc can we start push it up to 70hz??
I experimented with lower scanrates when pushing max H pixels and severely reducing Hsync pulsewidth. As I wasnt using a scope, I guessed I was getting around 11-13Khz. Pushing it in the other direction could increase VBlank rate. However, you would then start losing some Horizontal real estate. Perhaps a H res. of 512px is a good compromise?
If you could get to 75Hz you could also triple dither for lots more colours (with the same amount of flicker) or have the 240 ish colours but a reduced flickering.
Its a shame theres not some sort of reset bit on the VDC which forces a VBL. This would be very handy too, as it would increase the Hz more dramatically.
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Post by strobe on Nov 27, 2019 21:28:15 GMT
Its a shame theres not some sort of reset bit on the VDC which forces a VBL. This would be very handy too, as it would increase the Hz more dramatically. A vertical sync is triggered when the internal row counter = reg #7... So... What you could do in theory, is e.g. with a screen height (reg#4) of 240 rows for the sake of simplicity, set reg #7 = 100, and set a timer to trigger after the vsync occurs, say around row 130 which then changes reg #7=200 to trigger a 2nd vsync.
Then you have another timer to reset back to reg #7 = 100 again at like row 230, although you could just busy wait on the VBLANK bit for the last one. So that would give you 2 vertical syncs in one frame, doubling the vertical refresh rate. It would also give you "interlace' (in the c64 vic-ii sense of alternating screens) for free because it would show the top half of the frame as frame #1, and then the bottom half after the mid-screen sync as frame #2, then the top half as frame #3 etc.... I would call this something like VDC-DoubleRate. This would be the inverse of the vdc-split method in vdc101, which draws two frames with only one vertical sync pulse. And as with the vdc-split method, you could push it to 3 or more frames with enough fiddling with timers etc. But I don't see much point in this, as you would get more resolution in colour cell terms by having shorter colour cells - potentially 8x1 with VDC-FLI - by just having a short frame of e.g. 156 raster lines (half of PAL) which would give you 100Hz. As I'd prefer not to blow up my 1901 monitor pushing it to 100Hz+, I'll leave this for others to play with (obviously with the above I'm not touching the horizontal timing, which could alter the frame rate significantly in either direction)
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Post by oziphantom on Nov 28, 2019 4:13:23 GMT
well if you can lower the flicker say 70~75 hz, and using interlace you still get more pixels than 200, it will be smaller on the screen but it will also still fit in 16K. You can still get some colour blending in 80col mode, but only 1 more colour(50%) where as the interlace method gives you 1-3 new colours per base colour.
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Post by nikoniko on Jul 26, 2023 2:47:07 GMT
I looked into the color composite thing a few years ago too and came to the conclusion that it isn't possible without some additional hardware. The reason it works for CGA is that the PC is adding a color burst signal to the output, so even though it may look like the card is sending monochrome when using a 640x200 mode, it's sending a color signal along with it. For someone knowledgeable in electronics, I'm sure it'd be possible to rig a device that accepts the C128's monochrome output and adds the subcarrier to output a color composite signal. 3.579545MHz crystal oscillators for the necessary timing are readily available. A knob could even be added to tweak the phase, which would allow different palettes. Sadly, I'm not such a person.
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Post by gsteemso on Oct 29, 2023 23:23:17 GMT
I'm slightly confused by the conclusions here. The previous post to this one states outright that he checked the hardware, and the 128's 80-column composite signal contains no colour subcarrier, so there is no decoding going on that can be tricked. However, earlier posts in the thread made it sound like they had actually achieved the result. Which is it? Were all those pretty pictures only taken in VICE, or using a PC with a real CGA card, or what?
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Post by tokra on Oct 30, 2023 19:18:38 GMT
Depends on what "pretty pictures" you are talking about. Technically the VDC has only 16 colors, disregarding NTSC-artefact-colors which don't seem to work according to the posts above. Other than that you can only mix colors by using "software-interlace" = repeating the same frame with different color information. The "Colour Spectrum"-demo does this in the title-screen for example. True VDC-hardware interlace technically does not mix colors since the lines of the different fields are below one another, but visually the colors blend together to the human eye causing the illusion of more colors. Even so: If you mix 16 colors with each other you only get 136 colors: (n*(n+1))/2 - the rest are just duplicates. So claims of 256 colors are just bad math or just false, even moreso with 1024 colors of 65000 colors as the "Graphic Booster" claimed in the late 1980s.
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