I finally found the time during the Christmas holidays to build the MEGAROM by Bryce. It was a bit challenging for me as I had no previous experience with such projects.
I made the board myself, etched it with the hydrogen peroxide method as I'm scared of dangerous chemicals. I drilled the holes with my PROXXON drill which has perfect speed control and the shaft doesn't "play" at all. I don't have a base for the drill so I had to hold it in my hand while drilling. I used chips salvaged from various PCBs including the EPROM (27C1001) itself. I found an old SCSI 1 ribbon cable (50pin) which I adapted to connect to the CPC using an edge card IDC connector I salvaged from an old PCB once belonging to a blood analyzer medical device.
I have a TL866II Plus which I use with modern electronics but I didn't have an EPROM eraser. The Chinese ones are of very bad quality and the ones used by professionals are too expensive. I bought a cell phone sanitizer device from my local Chinese shop for 2,5 Euros (50% off). It had two small (but real) UV-C lamps and a little board. I put together a small box using cardboard material and aluminum tape. I got rid of all excess staff (like talking, it had a speaker) from the PCB and fed it 5 volts from my power supply. This thing can erase any eprom (and I tried a lot) in 12 to 15 minutes, I didn't expect that!
I used Protext along with a few games and programmed my EPROM, it worked the first time I tried it and I was in shock. I would like to thank Bryce for making this possible, it was a great experience for me.
Now, I have a question, I was hoping that by writing the Amstrad Diagnostics (Lower) at address 0 of the EPROM and then enabling the MEGAROM Rom 0 using the jumper on the board, I would be able to boot my Amstrad directly into the Diagnostics. Instead, my Amstrad keeps resetting after the Copyright message appears. How can you boot directly into a ROM other than BASIC?
A standard romboard doesn't support replacing the lower rom, and putting a lowerrom build in a normal slot will just crash (as you've found). Since your machine is already booting you should just install the upper rom version of the diagnostics rom, then you can launch it using
|diag
instead. If you have a non-working machine then it's not too hard to desolder the actual rom off the mainboard and replace it with a socket so you can put the diag eprom in instead. Or you can build a romboard specifically for replacing the lowerrom, Bryce even did one: https://www.cpcwiki.eu/index.php/LowerROM
Hi solidhit,
the CPC ROM0 is actually two ROMs. The lower ROM is where the firmware is held and the upper ROM is where BASIC is located. The MegaROM can only replace the upper portion of ROM0, so a ROM that needs to overwrite the firmware area (such as the diag ROM can't be used on the MegaROM.
Additionally, the lower ROM is a background ROM, whereas all other ROMs are usually foreground ROMs. You would have to ask the writer of the DiagROM whether it could be converted to work as a foreground ROM.
Can you post a picture of your MegaROM? I like to see versions of the device made by others.
Bryce.
Edit: seems like Pelrun was posting at the same time as I was :)
Thank you very much Pelrun and Bryce for your quick response.
Bryce, once more thank you so much for MEGAROM. I was suspecting the answer to my question but it now seems I have to ask the man himself if he can convert his ROM to act as a foreground one.
As for the pictures, here you are. The last one is my very own EPROM eraser which puts the best ones out there to shame!
20230112_144349-min.jpg
20230112_142431-min.jpg
20230112_142644-min.jpg
You don't have to convert anything, the public diag rom release zip comes with both lower and upper rom versions already.
https://github.com/llopis/amstrad-diagnostics/releases
Quote from: solidhit on 13:50, 12 January 23ut it now seems I have to ask the man himself if he can convert his ROM to act as a foreground one.
It's already available as a foreground ROM. When you download the zip file, there is a file called "AmstradDiagUpper.rom". Just use that and you are set.
Pelrun and Eto,
I didn't know that. Thank you very much!
btw: Amstrad diagnostics is of very little help as an Upper Rom. If the computer boots up until it executes a ROM, most things do properly work already. Running it from disk will be almost as good.
Quote from: solidhit on 13:50, 12 January 23Thank you very much Pelrun and Bryce for your quick response.
Bryce, once more thank you so much for MEGAROM. I was suspecting the answer to my question but it now seems I have to ask the man himself if he can convert his ROM to act as a foreground one.
As for the pictures, here you are. The last one is my very own EPROM eraser which puts the best ones out there to shame!
20230112_144349-min.jpg
20230112_142431-min.jpg
20230112_142644-min.jpg
Very nice... Just depressing to see that I was 13 years younger when I designed it ???
Bryce.
Never mind, now you're 13 years smarter and still people love to build a MegaROM. :)