Some Pleasing Experiments In 8-Bit Video Cards

These days, supply chain factors and high demand have made it incredibly difficult to lay one’s hands on a GPU. However, if you’re into older computers, you might find it hard to source old-school video cards too. Fear not, for [Dave’s Dev Lab] has been cooking up some experiments with a goal of eventually producing a new 8-bit ISA video card from scratch.

The long term goal is to recreate the original design of early IBM hardware, namely, the MDA and CGA video cards of decades past. The experiments center around the venerable Motorola 6845 which was widely used in computers in the 1980s. However, [Dave] intends to make them suitable for outputting to modern screens using typical VGA and DVI outputs, as well as those expected by modern TFT LCDs.

Thus far, [Dave] has achieved successful VGA output in a 40×35 text mode. With an 8×16 font, and the display running at 640×480 resolution at 60 Hz, everything hums along nicely. Similar experiments with a modern 480×272 LCD display have also worked well.

There’s a long way to go before [Dave’s] hardware is playing Commander Keen, but it’s great to see such effort being put into the platform. It could yet serve as a great upgrade for those wishing to use their vintage IBM metal without having to source a tired old CGA monitor.

We’ve seen similar work before too, with the Graphics Gremlin from [Tube Time] achieving a similar task. If you’ve been brewing up your own ISA hardware at home, do drop us a line.

Retro ISA Card Means Old, Slow Computers No Longer Need Old, Heavy Monitors

One thing about vintage computers is that they depend greatly on whether or not one can plug a compatible monitor into them. That’s what’s behind [Tube Time]’s Graphics Gremlin, a modern-design retro ISA video card that uses an FPGA to act just like a vintage MDA or CGA video card on the input end, but provides a VGA port for more modern display output options. (Actually, there is also an RGBI connector and a composite video out, but the VGA is probably the most broadly useful.)

Handy silkscreen labels make everything crystal clear. Click to enlarge.

Why bother making a new device to emulate an old ISA video card when actual vintage video cards are still plentiful? Because availability of the old cards isn’t the bottleneck. The trouble is that MDA or CGA monitors just aren’t as easy to come across as they once were, and irreplaceable vintage monitors that do still exist risk getting smashed during shipping. Luckily, VGA monitors (or at least converters that accept VGA input) are far more plentiful.

The board’s design files and assembly notes are all on the project’s GitHub repository along with plenty of thoughtful detail about both assembly and troubleshooting, and the Verilog code has its own document. The Graphics Gremlin is still under development, but you can also watch for the latest on [Tube Time]’s Twitter feed.

Thanks to [NoxiousPluK] for the tip!

The Modern Retrocomputer: An Arduino Driven 6845 CRT Controller

[MmmmFloorPie] revived an old project to create the retro mashup of a 6845 CRT controller and a modern Arduino Uno. When it comes to chips, the Motorola 6845 is the great granddaddy of Cathode Ray Tube (CRT) interfaces. It was used in the IBM Monochrome display adapter, the Hercules graphics controller, CGA, Apple II terminal cards, and a host of other microcomputer and terminal systems.

Way back in 1989, [MmmmFloorPie] was a senior in college. His capstone project was a 68000 based computer which could record and playback audio, as well as display waveforms on a CRT. The CRT in question was ordered from a classified add in Popular Science magazine. It was a bare tube, so the heavy cardboard box it shipped in was repurposed as a case.

Fast forward to today, and  [MmmmFloorPie] wanted to power up his old project. The 68000 board was dead, and he wasn’t up to debugging the hundreds of point to point soldered connections. The CRT interface was a separate board including the 6845 and 32 KByte of RAM. It would only take a bit of hacking to bring that up. But what would replace the microprocessor?

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A Comparison Of Early Graphics Cards

We have to admit, we expected to be bored through [The 8-Bit Guy]’s presentation, only to stay riveted through his comparison of early graphic card technology.

Some presentations get a bit technical, which isn’t bad, but what is so interesting about this one is the clear explanation of what the market was like, and what it was like for the user during this time. For example, one bit we found really interesting was the mention of later games not supporting some of the neat color hacks for CGA because they couldn’t emulate it fully on the VGA cards they were developing on. Likewise, It was interesting to see why a standard like RGBI even existed in the first place with his comparison of text in composite, and much clearer text in RGBI.

We learned a lot, and some mysteries about the bizarre color choices in old games make a lot more sense now. Video after the break.

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VGA In Memoriam

The reports of the death of the VGA connector are greatly exaggerated. Rumors of the demise of the VGA connector has been going around for a decade now, but VGA has been remarkably resiliant in the face of its impending doom; this post was written on a nine-month old laptop connected to an external monitor through the very familiar thick cable with two blue ends. VGA is a port that can still be found on the back of millions of TVs and monitors that will be shipped this year.

This year is, however, the year that VGA finally dies. After 30 years, after being depreciated by several technologies, and after it became easy to put a VGA output on everything from an eight-pin microcontroller to a Raspberry Pi, VGA has died. It’s not supported by the latest Intel chips, and it’s hard to find a motherboard with the very familiar VGA connector.

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(Better) Full Motion Video On The First PC

Ladies

Ten years ago, [Trixter] created 8088 Corruption, a demo for the original PC, the IBM 5150, that displayed full motion video using a CGA card and a SoundBlaster. It was hailed as a marvel of the demoscene at the time, garnered tons of hits when it was eventually uploaded to Google Video, and was even picked up by the nascent Hackaday.Now, ten years later, and seven years after [Trixter] said full motion video using the graphics mode of a CGA adapter was impossible, he’s improved on his earlier work. Now, it’s possible to display video at 640×200 resolution at 30 frames per second on a 30-year-old computer.

[Trixter]’s earlier work used the text mode of the CGA adapter, only because the 40×25 character, 16 color mode was the only graphics mode that could be entirely updated every single frame. It’s still one of the high points of the PC demoscene, but from the original video, it’s easy to see the limitations.

A while back, [Trixter] said displaying video using his computer’s graphics mode was impossible. He’s had years to think about this statement, and eventually realized he was wrong. Like the developers of modern video codecs, [Trixter] realized you don’t need to change every pixel for every frame: you only need to change the pixels that are different from frame to frame. Obvious, if you think about it, and all [Trixter] needed to do was encode the video in a format that would only change dissimilar pixels from frame to frame, and manage the disk and memory bandwidth.

After reencoding the 10-year-old demo for graphics mode, [Trixter] turned toward his most ambitious demo to date: playing the ‘Bad Apple’ animation on an 8088. As you can see in the video below, it was a complete success.

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Using Arcade Monitors With The Raspberry Pi

mame

Along with the growing popularity of the Raspberry Pi, we’ve also seen a related uptick in MAME arcade cabinet builds. Putting this $35 computer in an arcade cabinet makes a lot of sense, but connecting it to one of the monitors found in old arcade cabinets is a bit of a pain. Luckily, [Celso] figured out how to connect a Raspi to one of these 15kHz RGB monitors, making for a much more accurate emulation of old arcade classics.

The Raspi only has two video outputs – an HDMI port and an RCA composite jack. The old arcade CRTs have an RGB input, so directly connecting a Raspi to one of these CRTs is a no-go.

The solution comes from two converters: one to convert the HDMI output to VGA, and another video downscaler that takes the 31kHz VGA signal and translates it into a 15kHz RGB signal. [Celso] settled on the GBS-8100 video converter, a rather uncommon piece of kit that can fortunately be found on a few Chinese eBay auctions.

After connecting the old arcade cabinet power supply to the Pi, hooking up an audio amp, and converting the controls to USB, [Celso] has a very accurate MAME machine.