---
title: "The ET4000 in a Mega ST: Higher Resolutions, Eventually Working"
section: "retro"
tags: "retro"
description: "How an ET4000 ISA graphics card ended up working in a heavily upgraded Atari Mega ST, and what it took to get there."
layout: base.njk
parent: "/retro/"
---
<h1>The ET4000 in a Mega ST: Higher Resolutions, Eventually Working</h1>
<div class="detail-content">

<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. Getting one running in a heavily upgraded Mega ST turned out to be a genuine hardware battle, but the ET4000 now works in my Mega ST 4 "High" machine.</p>

<h2>What Made It Difficult</h2>
<ul>
<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>
<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>
<li><strong>Heat with nowhere to go</strong>, the card runs hot, and the Mega ST case has zero provision for active cooling.</li>
<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>
</ul>

<h2>How It Got Working</h2>
<p>Solving it came down to giving the supply the headroom it needed. With a properly beefed-up power supply to cover the 5V and 12V rails, plus a cooling solution for the card, the stability problems went away. The ET4000 now drives higher resolutions and more colors than the Shifter chip can natively produce, turning the "High" machine into a genuine workstation.</p>

<h2>The Context</h2>
<p>FPGA cores on MiSTer and MiST still only emulate the native ST Shifter, with no ET4000 emulation on the horizon given the FPGA resources it would require. So the real hardware approach remains the only way to get those higher resolutions, and now it works in the Mega ST 4 "High" machine with its dedicated monitor.</p>

<p class="note">Lesson learned: "just add a graphics card" on 40-year-old hardware is never "just" anything. But with the power supply and cooling sorted, the ET4000 now runs where I always hoped it would.</p>
</div>