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25

VGA's 640x480 mode was the first to offer square pixels and an exception among all VGA modes available (320x200, 640x200, 640x350 and 720x400 for Text). Square pixels weren't the standard back then. Adding video modes in later (Super) VGA was kind of a marketing game to offer higher numbers to outpace competition. First it was Colour, like offering 640x480 ...


9

Your problem is mostly going to be rep movsb changing that to use rep movsw should help. If the VGA card is on a 8MHz (or 6MHz) original AT bus then the timings work like this: 3 cycles to read or write a byte 19,200 bytes being moved. 345,600 bus cycles per copy 8,000,000 / 345,600 is 23.14 copies per second. 6,000,000 / 345,600 is 17.36 copies per second. ...


7

I have this monitor, which I think is a Commodore 64 monitor. Not really. And especially not for the C64. The screen was manufactured in Taiwan (*1) for/by Philips. It was widely sold as a monochrome screen to many countries. What is true is, that Commodore OEMed it ca. 1985 as 1901(*2) or later 75BM13 (*3) for/with the PC10/20/... series (*4) of IBM ...


7

Quoting Wikipedia, it seems to be at least two factors: The availability of inexpensive LCD monitors has made the 5:4 aspect ratio resolution of 1280 × 1024 more popular for desktop usage during the first decade of the 21st century. (from here) The 1280 × 1024 resolution became popular because at 24 bit/px color depth it fit well into 4 megabytes of ...


7

You are seeing dot crawl which is common when sending composite video into a low quality comb filter such as in that Video to VGA Converter box. To get rid of it, you will need a better comb filter (good ones are hard to find) or avoid composite entirely by converting from the STE's analog 15 kHz RGBHV to either the 31 kHz VGA that your monitor supports, or ...


7

1280x1024@24-bit fits in 4 MiB. Why wouldn't you take extra screen space? Keep in mind that games didn't usually run in 1280x1024 at the time. Back before LCDs became the dominating screen technology, you didn't care about the "native resolution" of the display - you didn't get the ugly "one pixel is stretched over two physical pixels, its neighbour only ...


6

The monitor shown is a Philips BM7523 which is a 12 inch amber monochrome MDA/Hercules display. The cable shown in your photo ends in a DE-9 plug which is standard for MDA, CGA, and EGA. (VGA uses a DE-15/HD-15 connector.) The service manual with specifications is here. First, you might be able to put your VGA adapter into a mode whose timings are ...


6

For the ST, the best option I’m aware of is to use the Atari-provided SCART cable and the OSSC; the latter will double lines etc. to produce a picture which any modern HDMI screen should be able to display. Depending on the outputs from your C64 (which may need to be modded anyway), the OSSC might not be appropriate; the RetroTINK 2X supports S-Video, ...


6

When VGA was designed and released, it had only maximum of 256 kbytes of video memory. The memory of VGA is arranged to have 32-bit interface to the VGA chip to have four byte planes in parallel. Therefore there are only 64k addresses of 32-bit video memory, and data of up to four planes can be accessed with a single CPU access. The VGA board can be ...


4

For the home market, TVs were often used because of their easy availability: most households already had one, and the image was often good enough for the low resolution of early machines. Professional users would often buy a purpose-made computer monitor, which would become essential as display resolutions increased and computers entered the GUI era. I'll ...


4

The VGA design is inherited directly from the EGA design, though with a few extra features. Most considerations apply equally to both. Although it is possible to treat the EGA or VGA memory as four banks of 65,536 octets, the EGA was designed to let it be treated more usefully as 65,536 groups of four octets, where each group had a single assigned CPU ...


3

A few 'home' computers from the '80s could output a VGA signal, including:- Acorn Archimedes Commodore Amiga (with Flicker Fixer) PC clones that had VGA on board or could take a VGA card (eg. Sinclair PC200) But for the vast majority that didn't produce a VGA signal you need an upscaler. Computers that only had RF output, such as the ZX81, ZX Spectrum, ...


3

In the 16-bit 8086, addressing of the memory space was done with a two-register pair Segment:Offset. The Segment register (there were four of them) addressed the high 16 bits of the 20-bit addressable memory, and the Offset register addressed the low 16 bits. So The effective address was computed in the CPU by: EA = 16 * Segment + Offset So, in order to ...


3

Sony DSC-1024 works great with both ST and C64 (or any other retro analog video). Outputs to VGA CRT, LCD, etc. Can often be found used for <60 GBP. You'll need the right cables for the computers. This is professional gear that used to be popular with broadcast studios. That's why the analog (VGA) video that it outputs is relatively "pristine", even when ...


3

If you're willing to modify the C64, there is a fairly recent mod that replaces the C64 modulator circuit with an FPGA board that generates an additional YPbPr signal by snooping the VIC-II chip signals. You don't mention what inputs your "modern TV" has, but component/YPbPr is more likely to still be supported rather than S-Video which is your other option ...


2

If the background is static it looks like you could skip doing the copying. Move step 7 outside the loop or skip it when the background has not changed. Keep a set of dirty rectangles for each frame. The flow for each frame would be: Save new dirty rectangles. Draw new Spites. Flip so this frame is displayed. When this frame is no longer displayed restore ...


2

It's a bit more difficult. The standard VGA registers allow a wide variation of modes and timings. Essentially you can use any frequencies you want, within the limits and resolution of your specific card. Early analog monitors are different: Some have fairly tight restrictions on the frequencies and timings they accept. So you needed to program the ...


2

How do I implement the text mode. The usual method is to send the video data Byte to the 8 higher address inputs of the character ROM to select the character pattern, and the low bits of the video line counter to the low ROM address inputs (eg. A0-3 for an 8x16 font) to select the pattern row. The character ROM then outputs 8 bits which are latched and ...


1

(Preface, this is RC.SE, not EE.SE, so less appropriate for such questions - so I wont go into schematic details) a) Video RAM Access As usual there are many ways. The most common are synchronizing CPU speed and video to use 'the' other half. Or separate both RAMs and access only during pause. Or use a dedicated video chip already offering separation. - ...


1

More a hint than a real answer: There where several quite successful PC families in Japan with only partial IBM compatibility. Most notably NEC's PC-98xx series which used several non-IBM pinouts for their graphic cards, including a 25 pin and a 15 pin variant. It would make sense for Mitsubishi to have their own connector when an adapter was needed anyway ...


1

I still have a small CRT TV in my house (belongs to my landlord) which has a composite video input on the front (which can still be used with a Raspberry Pi), and a SCART socket on the back. The latter is used with a digital TV receiver, as the analogue TV signal has long since been switched off. For context, this is in Finland. In the UK, I remember the ...


1

Some background: TVs of the area before video recorders, satellite receivers etc became common and worked best with a baseband video connection, did have little reason to offer such a connection. Neither would such a connection have been trivial to implement or retrofit. TVs of that era were very commonly of a so called live chassis design, which made it ...


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