Commodore 64 from PAL to NTSC
14 October 2024
C64 Music Keyboard
10 March 2025
Let’s make a ROM for the Sinclair QL
The Minerva firmware for the Sinclair QL lets you test the RAM at start-up and provides an updated operating system for this computer.
The QL uses dated memory chips, and to replace them with new EPROMs you need to adapt the pins and more: the CS signal on the old chips was active high, whereas on these it’s the opposite.
So the signal needs to be inverted. You can do this with an inverter gate, but these often come in packages of 6 gates in DIP format, or as a single gate in some SMD formats. To simplify the circuit I used a simple transistor to invert the signal.
Below is the schematic I made
Now let’s make the PCB with the help of PCBWAY
Through this Link you can find the project.
You can download the Minerva firmware here:
https://dilwyn.qlforum.co.uk/qlrom/index.html
I used version 1.98
If you need to decode the codes it shows you in case of a RAM fault, you can go to this page:
https://retrofixer.it/ql-minerva-ram-decode/
You can also find all the components you need on the page GitHub
A THT version has now been added too, to make assembly easier for everyone without using SMD components.
Finally, if you want to see how it’s made and how it performs in an actual test, don’t miss this video.
3 Comments
Is there any place that you can buy this fully assembled? My old eyes are not up to surface mount soldering
Hi, unfortunately I had made 5 and I gave them all away. It is not worth it for me to make them for you because then the shipping, if not in Europe, would cost much more than the object.
If you want I can make you a THT version and upload it to GitHub or PCBWAY as I did with the one you saw.
GitHub Updated with THT version.