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27 lines
2.0 KiB
Plaintext
27 lines
2.0 KiB
Plaintext
---
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title: "Why an ET4000 Graphics Card and a Mega ST Don't Mix (Yet)"
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section: "retro"
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tags: "retro"
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description: "A cautionary tale about pushing 1980s power supplies past their limits with a modern-ish graphics card."
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layout: base.njk
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parent: "/retro/"
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---
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<h1>Why an ET4000 Graphics Card and a Mega ST Don't Mix (Yet)</h1>
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<div class="detail-content">
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<p>An ET4000 ISA graphics card, adapted to the Atari MegaBus, promises higher resolutions and more colors than the native Shifter chip can dream of. In practice, bolting one onto a heavily upgraded Mega ST turned into a lesson in power supply physics.</p>
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<h2>What Went Wrong</h2>
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<ul>
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<li><strong>Power supply overload</strong>, the stock Mega ST PSU simply wasn't designed to feed a MonSTerBoard, an ET4000, and a MegaBus adapter at the same time. The 5V and 12V rails ended up right at their instability limit.</li>
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<li><strong>The missing -12V</strong>, the ET4000 needs -12V for its output drivers, usually tapped from the RS-232 port, adding yet another drain on an already stressed supply.</li>
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<li><strong>Heat with nowhere to go</strong>, the card runs hot, and the Mega ST case has zero provision for active cooling.</li>
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<li><strong>Signal integrity issues</strong>, the ISA-to-MegaBus adapter introduces reflections at higher frequencies, and access to ET4000 RAM is roughly 65% slower than native ST RAM, with no hardware BitBLT to make up for it.</li>
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</ul>
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<h2>The Practical Fallback</h2>
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<p>FPGA cores on MiSTer and MiST only emulate the native ST Shifter, there's no ET4000 emulation on the horizon given the FPGA resources it would require. The real answer for higher resolutions turned out to be software: Hatari running in VDI mode on a Raspberry Pi 400, which comfortably delivers 1280×768 with far more colors and zero PSU drama.</p>
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<p class="note">Lesson learned: "just add a graphics card" on 40-year-old hardware is never "just" anything. The ET4000 project isn't dead, but it's shelved until there's a properly beefed-up power supply and cooling solution to go with it.</p>
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</div>
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