exxos's Atari, Amiga & retro forum

Ok, so despite the fact that the 6116 and 4016 are completely pin compatible, if I swap the 4016 in in place of the 6116 and vice versa, then the machine doesn't boot.

With just the 6116 fitted in its original location (U3) the machine boots, which seems to affirm that U3 is the lower 2K of the RAM where the screen and colour info are located.

That means that U4 is the user RAM.

I'd expect U4 to work in the place of U3 given they are pin for pin, size and speed compatible, but no.

With just the 4016 fitted in the U3 socket, I'd expect it to boot, like it does with the 6116, but the data pins are doing nothing. I see some lines on screen, basically corruption, so I can't help but think that the 4016 is dead or severely ill.

I should say that at this point, the address, chip enable and write enable activity all matches, but I just get no data on the bus with the 4016 in the U3 position.

If the 4016 is in its original U4 location and the 6116 is in the U3 spot, then there is data on the bus at the 4016 and it boots. It's all kind of odd. The 4016 does have lower output levels at the data pins at the U4 position, but not by a lot and still within TTL specs.

I can't help but think there is definitely a RAM problem, so I'll just have to wait I guess until the parts arrive. Aside from the messed up colours the machine seems to run ok.

Well, the replacement RAM is here, and:


We are back up and running again!!

Turns out it was U4 that was at fault, not U3. 50-50 chance and I blew it, but that does explain why the machine didn't work with the old U4 swapped into the U3 position.

Next bit to fix is that Z key, about which I have some ideas already :)

:yay2:

Now, what fun things have you got planned for it?

stephen_usher wrote: 13 Jan 2022 15:25 :yay2:

Now, what fun things have you got planned for it?

Well, theres the Z key that I need to come up with something for, then I have some expansion boards to build, one which will also expand the RAM out. Then I need to find some software for it, but I may use it for a bit of Z80 ML tinkering, because it has a very simple memory map, it's a good place to learn :)

Managed to get a bit of time over the weekend for one of the Aquarius projects, the Micro Expander.

It's a small cartridge that plugs into the ROM port and adds a few tricks to the little machine, details here: http://www.bhabbott.net.nz/micro_expander.html

I should be able to finish the RAM part as I just need to program the ROM and GAL, which I have, and confirm the jumper requirements.

Once the remaining components arrive I can finish the top part, which adds USB and from there, access to ROM files off a USB stick :)


Altogether a very neat little expander.

Then I need to fix that damn Z key!!

EDIT: Looks like a little rework is needed on the headers, should go this way:


I thought it seemed a little cramped when assembled!!!


In my defense, the silkscreening led me to assemble it this way, and the site doesn't give great instructions. We all make mistakes :oops: :lol:

So, I fixed my faux pas over lunchtime :)

Just for comparison:


The board on the left is a Mini Expander and the right is the Micro Expander.

The differences I can see between the two is that the Mini offers additional physical ROM ports and DB9 joystick ports, but since the Micro offers ROMs over USB, I think it's the better option for now.

Need to look at composite mods too thinking about it.

That "Micro" board is pretty big!

It's only "micro" in the same way that the "Mini Countryman" (almost the size of a Discovery) is still a Mini.

stephen_usher wrote: 17 Jan 2022 14:01 That "Micro" board is pretty big!

It's only "micro" in the same way that the "Mini Countryman" (almost the size of a Discovery) is still a Mini.

Just realised I transposed my Micro and Mini (Now fixed), but yes you're still right in your size comparisons!! :lol:

So I thought I'd burn the ROM and GAL whilst I had a moment, and try the RAM/ROM expansion, leaving the USB/AY-3-8910 module off whilst I wait on the parts to finish it.

The good news is that it works!!


This is the new front end on boot.

This is the basic prompt, where we can see that there are USB extensions and 32KB of RAM in total:


So happy days :)

:dualthumbup: :yay: