exxos's Atari, Amiga & retro forum

Well the final parts for the Atom build have just arrived:


If I can get a chance between family emergencies I will get the EPROM burned and have a test boot...

How exciting.

There are a few odds and sods that are still to be installed, like a 6522 and some external sockets, but for now it's enough.

Wish me luck!!!

:crossed1:

OK, so some progress, but not quite where I'd like to be. It powers on and I get an image:


So for me this at least tells me I have a working 6847 and associated video circuitry. It also perhaps tells me that the video RAM isn't being cleared because no code is running. Now I have checked the CPU clock and I'm getting a clear 1Mhz signal at pin 37 of the CPU. I haven't looked at address/data pins yet but I'm pretty confident my ROM isn't being seen. The replica can use ROMs from 2764 up to 27512, so I'm using 27256's.

However I don't know what any of the jumper settings do and the ROM enable, pin 20 (I need to check 22 as well), is just high all the time. Also, behaviour is the same with or without the ROM, suggesting the ROM is not being read.

I'll post as well on Stardot, see what folks over there suggest.

@rubber_jonnie that's still a pretty good start though. Do you have a 2764? It might simply be that on the 27c256 the rom file is "in the wrong place."

PhilC wrote: 05 Mar 2026 22:25 @rubber_jonnie that's still a pretty good start though. Do you have a 2764? It might simply be that on the 27c256 the rom file is "in the wrong place."

I do but I'm not sure what ROMs go where as I have a single 16KB ROM file that's supposedly got everything in the right place. Of course it may not, but I suppose I could read the ROMs you sent me and have a play around with that.

OK folks we have liftoff!!!


After a lot of help over at Stardot (Atom build help thread) I had the machine at a minimal bootable configuration and had just pulled the all the remaining logic ICs and tested them, all being OK.

While I was there I pulled the CPU to see if it made a difference and it didn't, so I dropped in a spare CPU and voila, Acorn Atom prompt and working basic :)

I'm pretty confident that the CPU should have been working but I can only assume that it does but not in all machines. Annoying, but there we are.

I have one key that doesn't work so will swap that out for a spare switch I have.

I need to start re-adding the other IC's now, though they all tested fine anyway.

:cheer: :cheer: :cheer:

Well done Mr Jonnie.

I'm going to look at overclocking mine to 2 and 4mhz at some point too.

rubber_jonnie wrote: 10 Mar 2026 13:48 OK folks we have liftoff!!!

:2k2: :girldance:


@exxos Approves your "wallpaper" :P

Glad to see that you've beaten it into submission!

:thumbup:

exxos wrote: 10 Mar 2026 13:52

rubber_jonnie wrote: 10 Mar 2026 13:48 OK folks we have liftoff!!!

:2k2: :girldance:


@exxos Approves your "wallpaper" :P

:lolbig: