Adapted from Arduino Nut Blog  -  PL8-2 , dated 8 October 2009
see also atom    Blog by Charlie Robson

AtoMMC 2.0     See the final version atommmc2   i.c. K.v.Oss    here  of in NL

My children used to refer to C3PO as R2D2's dad. Funny how those minds work, isn't it. I used to think that real fun could never be anything other than corporeal. That just goes to show. This is the most fun that I've had in a while :)

It's the V2 incarnation (can that be right? There's no meat here..!) of the PL8 MMC interface.
Here she is, in full component-side glory.

The TTL is a simple read/write decoder. The port onto which this fits provides rough address decoding. I wish it would shave. I hate the chafing.

But I do so love the wiring.
It's a PIC - one of those manly sorts with the parallel slave port. I know it's terribly incorrect to use the word slave - oops I used it again! sorry! but that's just what it is. So the parallel slave port behaves like a chunk of selection logic and wakes the PIC when a read or write occurs. There are /RD and /WR lines.
The microcode on the PIC latches data ready to be presented on a port when the /RD line is asserted. No delay, it behaves just as a latch would.

Similarly asserting the /WR line will latch the values present on the data bus to a register. Interrupts ensure that these events are recognisable and the remainder of the uC code is shuffling data to and fro.

The performance of this type of interface is already documented in another post <> milliseconds to load programs <> so I won't go into it here.

Needless to say schematics and code, both micro and 6502, are available if you'd like them.

The Atom needs some non-volatile random access storage. I ran out of suitable patience burning EPROMs when updating the firmware for the new MMC board. The old firmware was developed with the aid of an MMC simulation that I shoehorned into the MESS emulator. The simulator allowed me to code against a just-accurate-enough model of an MMC card in SPI mode. The new interface doesn't have such a luxury yet. So I got thinking, and decided that the 32kx8 FRAMs that I got from Ramtron recently would do as an EPROM replacement. But I'd still need the firmware in EPROM available to bootstrap from... Hmm. I'd also been meaning to build a copy of a neat videoram replacement card that I found in an Atom belonging to a friend. So that was that, really.

Or rather; At the moment it's only the video ram replacement side of the equation. The flying lead takes A10,11,12 from the main board. The rest of the signals are picked up from the vacated 2114 sockets. The empty socket is going to take the FRAM and some decoding logic will live adjacent, unless I can find suitable signals to pick up from the motherboard.
Not all underbellies are soft; This was quite hard, actually:

It's a nonsense title for a post, but I was just thinking of Frankie Howerd.
I have a shameful admission. I lied in my last post, or at least mislead you, dear reader. There were 5 projects - though I suppose the scale of this one didn't really register on the need to win scale.
I made a mega-rom adapter for my Atom. I haven't inserted a large image for a while (Matron!), so here goes.

The mega-rom! In an Atom! It allows me to page in one of 16 4k images into the address space allocated to utility software in the Atom's address map. The switch carried with dignity at the end of the cable allows a user to perform the magic. But you probably worked that out.

Don't you just love the green and yellow striped electrical tape? I was speaking to an electronics fashion pundit at the RCM event and they told me (in the strictest confidence) that this years projects simply must have green and yellow electrical tape! Being the capricious sort that I am I simply have to agree, at least for today.

I have been expanding my horizons, not to mention my old computers - ha ha, with contraptions such as this, fabricated with board spacers and socket strip. These nifty connectors are ideal for making up adapters like the one above.

Pictured A board spacer is sized up by an interested socket strip I've tried a number of different makes but these are by far the best - If I were Victor Kyam I'd buy the company. Which is SamTec if you're interested. No, I'm not receiving a back-hander. Though if you're reading, SamTec - well let's just say I'm interested... ;)
There is a slight wrinkle in the construction of these boards. The socket has to be mounted on the same side as the pads. I've yet to find a supplier of through-hole plated proto-board, but when I do I'll use it for this purpose. In the mean time, I use one of two methods. The first involves a 'cost efficient' socket - the pressed pin variety. Splay its legs akimbo and apply solder. Place it right-side-up on the padded side of the (woeful , now I think of it) protoboard that my local electronics supply chain provides. It rhymes with Craplin if you're wondering. Affix to the board with a swift application of iron. Bingo! The 2532 adapter for the tier jerker was manufactured using this method. Apply your eyes to the previous post for a fine example.
The second method, as used here, involves the socket strip. Place this adjacent to the spacer, at chip's width naturally, and solder the pad to the socket where it meets the board. You need a fine iron and a steady hand for this so no beer or porn beforehand. Ooh which reminds me... What?? Oh hush, I'm not soldering tonight.

Here you see socket strip and spacer conjoined with solder bridges. Which are surprisingly hard to make intentionally!
Lordy I've wittered on long enough. I have an SD2IEC to attend to. Please excuse me :)
I couldn't make it work. I tried... Alas the Fail was strong in this one.

The spectrum wanted its CF adapter. I wanted to oblige. I tried a number of different cards which all appeared to be lacking in Win. I had checked over the wiring a number of times and, although not entirely convinced it would help, I thus set about rewiring the beast.

Guess what! Still no Win. The board resolutely refused to

play nicely and so I took a step back and considered all the possible failure points. Too much stray capacitance? A dry joint? Lack of understanding? The list goes on. At last I decided to cut my losses and re-work the board as an IDE interface. Several tens of minutes later, having used an entire roll of desoldering wick, the board was bare but for the edge connector.

It's a good job
The result"

Joy! I'd carefully checked each connection as it was made and I was certain they were all good. I'm bouyed by the assurances of my meter, and sure of at last securing a payment of success to offset the miserable week spent futilely poking at the CF board. Apply power, insert device -..
With heavy heart I put this project aside until some future time when I can muster the strength of character to return to the joyless debugging. It didn't get much better than this for weeks. I've started four more projects since, each more resoundingly failful than the last!

So that, dear reader, is why there have been no updates. I'm afraid I don't have the strength of character to tell of my winless ways. I can't even bear to tell you what they are. I do intend to return, though, this time with bigger guns. More on that later.

What I needed was something simple to rejuvinate my mojo. To get me to the power-pill so I can start to chase those ghosts.

My opportunity came at a recent retro-computer themed event where I met up with a number of people thus far only identifiable by a 24x24 pixel avatar and psychologically revealing nickname. Amongst these a contact who keeps me fuelled with rare Acorn Atom goodies. In this case I was knighted with a home-built rom-box, containing a couple of eproms.

Forget the soviet nuclear-warhead launching switches! The mysterious dials and socketry - this is truly a thing of beauty. But like most beautiful things, it's what's inside that counts. And that was going to be ME. The dumping challenge was on! [If you or someone you know built this rom-box, then please get in touch!]
Once retrieved from the secure caress of their sockets the lovely ceramic packaged gold legged EPROMS were quivering in the palm of my hand like frightened baby Meerkats. These chips are ancient and JEDEC incompatible. 2532s. 32Kbit arranged as 4K x 8. Here is the adapter I built to allow me to read the eproms using the glorious.


            And in situ:

As it turned out they contained images of programmers' toolkits. I must admit I was hoping for a rare find, however the images in question are already well known. But that is by-the-by. The thing is an hour had been spent with a soldering iron, a further hour spent reconfiguring the client application to draw the data PC-ward by the magic of electon in serial cable, and then some moments of joy - as the contraption worked. Worked?? WORKED!

I believe my drought is ended. The rains of win are falling, filling drained butts of enthusiasm. I shall venture forth and tackle the next item - Upgrading my SD2IEC in order to take advantage of the JiffyDos-enabled commodore machines at my disposal..


What a mess! But it works - sometimes :) All that stray capacitance - well someone's got to give it a home.

This is what I'm forced to do because the Stag PP39 EPROM programmer that I was so generously given by a fellow FreeCycler works well, but for its serial connection. Ho hum. Wanting to burn an EPROM to hold the driver code for the Atom MMC interface was the necessity that was the mother of this frightful invention. In a fit of pique I had the idea that I should create a 3-step process"Burn my code into an EEPROM, transfer this to the programmer's buffer, and thence into an EPROM! Why not just use the EEPROM for my project? An astute question, esteemed reader. Well the type of EPROM expected by the Atom is an olde-fashioned marque with a subtly different pin-out to the more contemporary (read"standard) 27x series. Luckily the PP39 can burn the 2532 that was required. Even luckier I suppose is the fact that I had one of these! An adapter board can be made to facilitate the harmonious interfacing of the disparate breeds, but this would involve less lashing-up, you see? And we all need a jolly good lashing from time to time.

I digress. What you see before you (or more correctly above) is an ls299 accompanied by a brace of ls164 shift registers. These in turn are connected to an 8k Atmel EEPROM. In the driving seat you see the Arduino and - naturally - a poor but functional MMC interface. The 164s are in charge of address generation, and the 299 has bi-directional data line duties. It's a simple and effective design which I have referenced before.

I've developed the Atom MMC driver in assembler, naturally. This time I opted for cross assembly. If you saw the code attached to my previous post (my - is that the time?) you may well understand why - the inline assembler is hard work with its terse labelling syntax. I develop and assemble on a PC, using a custom Visual Studio workspace and a freeware 6502 assembler. The resulting binary is debugged as far as possible using Wouter Ras' brilliant though tricksy DOS Atom emulator. When I'm happy with the code it gets put on the MMC card and burned to the EEPROM using a subtle combination of swearing, crossed fingers and sacrificial chickens. The burning process needs to be attempted a fair number of times (the stray capacitance, bless) until the verify step passes and I can be sure the lash-up has worked. Once transferred to the programmer, the code fizzles its way onto a freshly UV-cooked EPROM and then into its warm and welcoming bed - Socket IC24. And so to work:

Presenting - the MMC adapter I built to fit on the venerable machine's expansion port, as visible here.


And in situ:

Goodness - that is the time! Two and a half months this post has taken me! Either that or my post-Sachertorte coma was deeper than usual... Whatever, forgive me. I am off to play Atom Invaders - which now loads in under 3 seconds, a far cry from the original 5 minutes of the tape version! I'm getting back into the Atom swing! After a fruitless hour measuring incorrect logic levels at the Atom's expansion port I was on the verge of giving up. I had been prodding the VIA, according to available documentation, and getting nowhere. All I wanted was a toggly bit. Was that too much to ask for? That's when I decided to do some chip swapping.

It takes me longer than most people to get to this point as I'm a software person at heart and so blame that first ;)

I just happened to have a vintage 6522 VIA lying on my desk so I swapped the chips over. Joy! I was flipping bits like a demon. Naturally my thoughts turned to MMC...

60DIM LL(13),C(6)
80F.N=1TO2; DIM P(-1)
90P."PASS "N',$21
110\ main
120:LL0 LDA @#0
130STA C+1; STA C+2; STA C+3; STA C+4
140LDA @#95; STA C+0
150JSR LL3
160LDA @#40+#0; JSR LL7
170LDA @CH"1"; SBC @0; JMP W
180\ select card
190:LL1 LDA @0; STA V; RTS
200\ deselect card
210:LL2 LDA @#20; STA V; RTS
220\ init hw and go spi
230:LL3 LDA @0; STA V+#C
240LDA @#FE; STA V+2
250LDA @#20; STA V
260LDY @10
290\ xferbyte
300:LL5 STX T+0; STY T+1; LDY @8
310:LL6 PHA; AND @#80; STA V
320ORA @#40; STA V
380LDY T+1; LDX T+0;
400\ command
410:LL7 STA C+5; LDY @5
430:LL9 LDA @#FF; JSR LL5; AND @#FF; CLC; BPL LL10
440DEY; BNE LL9;
460:LL10 RTS

If you're an ex-atommer or you've been around BBC micros you might recognise this. If you don't then I can tell you it's some Atom basic with inline assembler. The Atom's Basic dialect was hard on the eyes but lightning fast. By the standards of the day, naturally ;)

The built-in assembler gave the user of this machine an instant boost when learning to program. No fussing with 3rd party apps, loading the assembler or machine code, or the attendant problems with cassettes. Turn on. Assemble. Bam! (Which is as it happens almost quite literally what happened to my 1st Atom over 20 years ago...) Now if only it was that easy for the kids of today - it was much better in the old days - I remember when all this was fields etc. etc.

The above listing is code to bit-bang SPI to an MMC card attached via the simplest of hardware harnesses to the rear expansion connector of the Atom. I'm looking at making a ROM based solution that hooks into the OS's filing system vectors. It's all quite primitive at the moment but I'm hoping it'll solidify. Get in touch if you have any experience of developing this kind of Atom program. I'd love to talk to you.

She's arrived! After many years of fussing and prevaricating I've finally taken the plunge and bought myself an Atom. The prices were rocketing in the bay of E, and I reckoned on the time being nigh. This one was advertised as having a broken key and otherwise with little hope of receiving a working box I decided on taking a punt and fixing it up if necessary. I've always loved this machine. I owned one as a boy although it was only a half-populated board without a case. It still did the business though!
I must admit to being a little saddened when I opened the wrapping. It was grubby and half of the keys appeared to be smashed in, sitting a good 6-7mm lower than their neighbours. The 1st thing was to open it up and check the power supply status. The Atom was infamous for overheating and many owners bypassed the internal regulators in favour of feeding it a regulated 5v diet.

As was indeed the case with this one. It had received some tweaks in its time, but I was really happy to see the work was all of a high standard. These were all what I call 'magazine hacks' - the electronic equivalent of a one-liner joke. Single wire patches for enabling an eighth bit on the printer port, joining some lines to an external socket for wiring a joystick, nothing major. I was chuffed to see that it was fully expanded memory and support-chip wise. 12K RAM & 12K ROM plus a utility kit that I'm still having trouble finding any info about. I'll have to resort to a disassembler I think. No colour board but then I wouldn't ever have even contemplated that. Too rare.

The mother and key boards were in a real state. I think it had been stored on top of kitchen cupboards at some point in its life and it had received a good layering of yellow grease and fibres. Some keys were sticking and this was the main reason. I've since scrubbed it with a toothbrush and plenty of warm soapy water and now you'd never know! I was shy of putting it in the dishwasher as some people recommend, this may be ok for generic PC keyboards but rare vintage '80s hardware...

At some point in its history the three keys in the lower left had been replaced. They were replaced with high quality keyswitches, which - well I never - made the keycaps sit higher. What had happened was that the previous owner had raised the original keycaps with superglue to match the height of the replacements. The original mechanism is a cheap spring-based creation which I've only ever seen in Atoms ... and a keypad that I was given recently! That was handy, wasn't it! So I hacked the keypad and replaced the switches with something contemporary and far more suitable. And the same height! The caps all came off and were cleaned and repaired where necessary.

The machine is now clean and tidy, ready for work.

One tough trick was finding a plug to fit the odd power socket dimensions. It's some olde fashioned imperial jack size. Eventually located with the assistance of an Atom owning colleague I was able to juice the old girl. To my immense surprise it eventually reset and presented me with the very comforting words:

ACORN ATOM  >            Joy!

A computer's no good without software, right? Like all good '80s machines this one needs some square-wave goodness. I couldn't locate any software to generate the required signals that worked on a modern PC, so being handy with a compiler I got to work. I'm pleased I did all the work on ACE - the techniques transferred instantly and I had a program to translate raw program dumps into WAVS. And text files into raw dumps. And vice versa.

I'll be happy to pass these on to anyone that wants them. The source can be downloaded here. It's vanilla C++. I'll be happy to help with porting, compiling or whatever.

There looks to be a new site emerging that could eventually be a must-see for any Atom fans. I'm speaking in the future tense as it's not there yet but I've spoken with the masters and they're promising big things.