Britvasion Part 2

Now I had my machines up and running, it was time for me to explore a bit more.

What lurks beneath the covers? Atari first look.

I started with the Atari. I opened it up. There was a rusty RF shield with a hole cut into it and a board sticking through, covered in packing tape. I removed the RF shield and packing tape and…

Surprise!

WHAT IN THE NAME OF ALL THAT IS CLEAN AND HOLY IS ALL THAT??!?

Yeah OK so there’s a lot going on in here, and with the aid of the fine folks over at the AtariAge forums, we were able to identify what’s going on here.

First over to the right, we have a 3 way ROM switcher swapping out the boot ROM.
I was able to dump all 3 “bonus” ROMs and identify them

They were rather… crusty. I have since cleaned them and stuck a proper sticker over the window on the bottom one

In order from top to bottom, they are: Stock ATARI BASIC, OmniMon, UltiMon, SuperMon (the previous owner must have liked Machine Code Monitors :-D)

The board is wired to the rotary switch on the front and that allows you to select what ROM you boot with.

Towards the centre is apparently a RAM upgrade to 256K (Edit: It looks like 192k so an additional 128k on top of the base 64k I guess?)

Suddenly I’m hungry for spaghetti.

You’ll notice that one of the wires (Top left) is detached. It’s not the only one. I have resoldered several of the wires at this point.

Now, a computer without any way of loading data is not very useful. Realistically, you are limited to typing in BASIC and that’s about it.

Thankfully I had thought ahead and ordered some bits and pieces to build a nifty input gadget called an SDrive-MAX.
A quick aside here: Just a reminder when ordering from China that you don’t always get what you think you’re getting, and stuff won’t always get to you. I ordered an Arduino clone in late 2019 that never arrived. The supplier was nice and responsive and sent a replacement… which also never arrived. The supplier also went unresponsive at this point, so I got a refund from the selling site. I was able to use the refund to order a replacement which arrived about a month later, followed, ironically by the replacement Arduino clone.
I also ordered a screen of a specific compatibility. Turns out it wasn’t quite compatible, so I have had to order a different one, this time locally.

I also had a friend 3D print a SIO connector, which came out quite nicely.

Isn’t that a lovely SIO connector?

SIO is a very clever connector, designed for high speed data, with a nice ability to daisy chain. Interestingly it’s designer was involved with designing the USB standard.

I chose to make one with external power, so I could start it up separately from the Atari. This would allow me to choose my file to load without needing to boot the Atari first. I did add an override switch in case I do decide to power off the Atari (Say, for taking it to demo somewhere like a computer-meet)

The mostly finished unit. I need to swap the screen.

While it does work, it’s a bit hard to use as the screen is slightly incompatible, so the text is weirdly reversed and it doesn’t fit the entire screen.

This was enough for me to boot some tests and generally confirm the machine mostly worked. A nice thing with this system is the built in diagnostics, including a keyboard and memory test. If only all systems had this! Hold down Option while you boot and there you are.

My next upgrade on the Atari would involve a major jump so I put it aside.

Connect All the Things! BBC Upgrades.

Now as I had got as far as I was willing to get in one go with the Atari, I started to upgrade the BBC Master system.

Fitting the SD Card was step one, as that would give me a library of software out of the box. It was pretty straightforward, with only two steps. It plugs into into the User Port on the base of the system, and a new ROM plugs into the onboard ROM sockets, of which the BBC Master has plenty ๐Ÿ™‚

(I really should look at what other ROM software I can get for this system. It’ll even take a ROM via a “cartridge slot” on the top!)

This is about the size of a slightly large postage stamp. It’s TINY!

It all went in OK but it took me a few tries and quite a lot of reading to get this under control. It also works differently under different versions of the BBC ROMs.

“What’s that?” I hear you say? Why yes, my BBC Master does have more than one version of the BBC ROM set. One of the other kits I purchased was a lovely kit from RetroClinic.com which gave me a rotary switch connected to a small sub board. This then replaces the default ROM and gives me a choice of ROMs.

That ROM visible immediately below the MultiOS board is the one for the SD card board
This switch sits inside a cutout designed to hold an optional modem. Clever, no?

The four versions of the ROMs correspond to different versions of the BBC Over the years. The first slot is those of the BBC Micro, for maximum backwards compatibility. It’s not perfect as the CPU has slightly different instructions, but it is much better than default. Next up is one compatible with the interim BBC Plus systems. Number 3 is the default version for the BBC Master and number 4 is the same as number 3 but with everything patched up to the last versions of everything. (Forward compatible!)

With this in place I was finally able to play most games. There are still a handful that don’t work but, eh, I have heaps of games now.

Note I was still working in Black and White at this point. By default the RF out gives colour, as does the RGB, but Composite was only B/W as it was designed for “productivity applications” such as word processing and spreadsheets in 80 column mode, and would therefore normally be plugged into a monochrome monitor.

I was having none of that. I’d done some research that suggested that, although designed to plug into a CGA style “TTL Signal” monitor, I could theoretically just drop some 330โ„ฆ resistors inline with the red, green, blue and synch lines and plug it into my beloved 15KHz monitor.

(Have I mentioned how much I love this monitor for retrocomputing?)

On the StarDot forums, when I asked, everyone seemed to thing it would never work, but I wasn’t going to let that stop me now, was I?

Yes that’s “BBC” written in Sharpe on that shell.

So I wired it all up, plugged it in and… it worked the very first go.

Colour! Glorious colour!

There’s a sneak preview in this image…

Once this was done, I added something I’d built way back when I first won the bid for the BBC. It turns out the venerable Gotek with FlashFloppy firmware supports the BBC Master. As I had a spare Gotek (Doesn’t everyone?) and all the parts left over from my work on the Atari ST, I had built up an external Floppy drive emulator for the system. It has an OLED display, a pizeo for “authentic” drive noises and a rotary dial. I even put it in a nice box with a pretty label.

Isn’t that nice!

The only complication is the power connection to connect to the BBC. It’s that red thing in the picture above. They are available. I got the part number an age and a half ago and hand to order it specifically from one of the specialist suppliers. I also had to order the pins separately.

It works a charm. Now I can put games in via the SD Slot OR via floppy disk. Ain’t life grand?

My final upgrade was to add another item from the same EBay seller who provided my SD Interface. This one was a PiTube Direct, an incredible product that slips inside the BBC Master on a small daughterboard. It mounts an emulator running on a Raspberry Pi 0 as a secondary processor for the BBC. Believe it or not, but this is a design feature of the original hardware. Acorn decided they wanted the system to be nicely expandable and added a “tube” connector, allowing a second CPU to be connected. The Raspberry Pi Zero can emulate some very fast versions of several co-processors that were common in the day. I could even run CP/M if I wanted to. (Which would give me four somewhat compatible CP/M systems… “Yay!”)

I had to solder on some header boards, so from past experience, I put the pin headers into the the sockets on the BBC, clipped on the board and soldered the outer two most pins of each header, before removing to finish it all up.

This assures the pin headers will go into the sockets later when everything is finished. Glad I did this as apparently the sockets on the board are crooked.

Once all done, I added it in, and after some arguments with the software I was able to get the tube detected and running fine. Only Executive Elite appears to use it out of the software I have tried so far, but it was a VERY cheap upgrade.

An Acorn containing a smaller newer “acorn”. (The A in ARM used to stand for Acorn)

The next step is actually out of order, but as it relates to the BBC, I may as well tack it in here before I go back to the Atari.

I built a joystick! Almost nothing uses it!

OK, so that’s not true… Elite uses it, and that’s reason enough ๐Ÿ™‚

Looking at some documents online about how joysticks for the BBC systems work, unlike everyone else Acorn did the joystick port right. This is a bold statement, but hear me out. IBM, Commodore, Apple and Atari all did their analog ports in a similar way. They relied on a fixed size potentiometer and measured resistance between the wiper and one leg of the potentiometer. This means you have to match the potentiometer to what the system requires. it won’t work otherwise. Many of these potentiometers they used are no longer commonly available. We have to kludge around this on a regular basis.

Not so on the BBC. What THEY did was put 5v to one leg of the potentiometer, ground on the other and measure what percent of the 5v was showing on the wiper. This means you can use any potentiometer.

As I had an old “playstation controller” style joystick built around a pair of 3 pole potentiometers lying around, unused from an older project, I decided to wire it up as a BBC Joystick. I made a simple circuit from some more experimenter’s board and a button I purchased. I stuck it all in a case for a remote control that I had also earmarked for the joystick project.

The silver sharpie marks are me positioning various pilot holes.

Back to the Atari

So now the BBC Master system was all running, I decided to do an SVideo mod for my system. I made up a cable, complete with Audio out and plugged it into my SVideo monitor. I got a black and white picture, which is what I expected.

This cable also outputs Composite and Audio as well as SVideo

I started working on the mod, trying to do as minimal work as needed.

I initially tried simply running a wire to the Chroma output but was still only getting black and white, so I dived in and started making each mod, one by one. The only change I didn’t make was the chroma feedback resistor.

Still no colour.

By now I was starting to panic!

I disassembled and reassembled my SVideo cable. STILL no colour.

Then I had a realisation. I checked the SVideo cable that plugged into the TV that my adapter plugged into. I touched it and it fell out of the TV. It had been loose the whole time.

Once THAT was plugged in I was getting lovely colour!

Success! It actually WORKS!

Apparently the game is called “Abracadabra”

I did find the Atari quite unstable so I didn’t do much with it initially, but about a week ago I opened it up to see if I could get more stability. I reseated all the chips and the ROM tower, and checked all the flyleads. One was only held on by gravity and another was close to coming loose. I resoldered both connections and it’s been pretty good since.

One final mod I made was the dial used to choose which OS ROM had lost the limiting lug somewhere along the line, so rather than limiting it to 4 ROM positions, it could freely rotate to 12 positions, 8 of which were “Your system doesn’t work any more”.
I fixed this by making a new lug out of a paperclip. It took me a bit of sleuthing to work out which hole the lug needed to be in to limit it to the four connections, but I was able to work it out in the end.
While working on the switch I decided the current switch was a bit ugly, so I went looking and found a HUGE UGLY switch. Of course that’s what it now uses ๐Ÿ˜€

That is a HUGE UGLY switch.

The Future

I have ordered a new screen locally for the Atari 800, which will hopefully allow me to use my SDrive-Max a lot more easily. After that I may try and get an AVGCart to let me fill in the blanks in my collection.

As for the BBC Master system, I honestly cannot think of anything more I could add to it, with the possible exception of some ROMs. I’m not even sure what ROMs I’d get for it. LOGO maybe?

Published by ilike8bits

I collect old computers and consoles

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