I didn't want to leave.

I visited an amazing shop a while ago. I wanted an oscilloscope and the local supermarket was right out, apparently, so a quick search on teh interwebs and this goldmine was revealed...

There was more around the corner and behind the outcrop on the right. And even then all stock wasn't accounted for. Despite this the owner knew every item intimately. Well, not in the biblical sense. Ahem.

This is what I went home with:

The top one - a Tektronix 465B. Yes, of course I wanted it *all*, but, you know, space. The prices were stupendous and it was obvious that the owner was a real true equipment geek. There were instruments in the rear recesses of the shop which were straight out of a gothic horror - brass spheres held aloft a glass tube encased in a brass and rosewood cabinet - an actual piece of test equipment used for measuring kilovolts on overhead wires. Huge knife bladed switches and variable resistors where the resistance was set by inserting plugs at intervals along parallel copper bars... And a pile of meters and programmers and signal generators and... what the... I have no idea what some of these things were.

And the smell... Divine.

Anyways. That was a while ago. I offered to advertise the establishment but the proprietor was busy enough without the additional traffic. But I'm sure that if you were within visiting distance of Reading, England and you asked...

http://www.stewart-of-reading.co.uk/

PL8-2, R2D2's Dad.

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.

Atom VRAM mod

I have really struggled with the question 'should I modify this rare vintage micro or leave it as-is?'

Well. The thing about the Atom was that it invited modification.

So I came.

To the party that is, the one that the Atom invited me to. Honestly. Some people.



This is the truncated version of the ill-conceived all-in-one memory board that I started some while ago. It's simply VRAM. Nice. Witness the burned-off resist at or about pin 15. Ahem. Ah well, it's all for the greater good. 2114s are not exactly super-rare, but they use so much wattage. It's not green, it really isn't.

Retro Computer Museum Open Day 2009

The organisation most commonly known as The Retro Computer Museum are having another all-day gaming event. For those in the UK willing to travel to Leicester you should visit their site and get the low-down.

I'll be taking a boot load of kit to fiddle with over the course of the day and I might even indulge in a little gaming. I'm mad like that, me.

MMBeeb

Not a voluptuous expression of joy for a broadcaster, but one of these...


... being an MMBeeb board. I have mentioned them before, but I've improved the design somewhat since then. This is from the last batch. SMT components and a rather cheeky regulator placement make these the tiniest and most comely batch yet. I like to make each one different, unique. Electrically they're identical but each has its own character. I like to talk to them when I'm alone.



An MMBeeb board plugs into the user port of a BBC Micro and coupled with some smart coding by the original creator Martin Mather gives the contemporary BBC Micro user the ability to have at their disposal literally thousands of disk images all instantly selectable and appearing as though a genuine 5.25" disk.

They're fast too, programs load in seconds. G'orn there Chuckie Egg!

Mending

Finally I've had some movement towards finishing a job. Really, it's been a long time :)

A poorly Atom belonging to a friend required a key switch fix. The keyboard on Atom motherboards of issues 1..4 is a strange all-in-one affair where the switch mechanism is a pair of counter-wound springs which connect when a weedy plastic plunger depresses them. They are puny and prone to breaking.

The only effective fix is to cut out the broken part and insert a new switch, as I believe I have blogged about before. This would be a new challenge as the switches I replaced before were at the end of a row and were changed as a unit. This time I would attempt a single unit as I have run out of replacement parts to do the two adjacent switches...

This is the first time I've used my callipers and I must say they're jolly useful.

Here's the replacement switch ready to be dropped in. The antennae were added so that the tiny whisker-like wires at the base of the switch would register correctly with the holes on the PCB. The replacement part is ever-so-teensily different from the one it's replacing, so registration wasn't guaranteed when sliding the piece into the anxiously awaiting gap. When the sides of the switch were coated with superglue that would have been a problem. The extensions fell away as expected when the solder joints were applied.


Hurrah!

Grzzzzzz!

With a Pic for a brain and a mouse for motion tracking you should consider your hiding options before the head-mounted laser gets added. You have been warned!