Sinclair Spectrum - 40th Anniversary

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Not sure if this is "General Electronics" (in a sense I think it is) or just "Off Topic"? 

 

Anyway on Saturday just gone the Sinclair Spectrum reached its 40th birthday. My small part in wrecking it (after Amstrad bough Sinclair and we brought out new models) is remembered in:

 

https://www.eurogamer.net/the-sp...

 

Reading the posts from my contemporaries (I worked directly with Richard and Rupert) brought back a major burst of nostalgia for much a more innocent, innovative, and politically incorrect era when it was actually fun to be involved in the development of technology.

 

(If you have a a +2A/+3 try typing the seemingly meaningless command "COPY RANDOMIZE" and then hold down the keys 'C', 'J', 'L' (my initials) within 3 seconds. I can remember going into Dixons on a Saturday afternoon and doing just that to leave their demo models of Spectrum showing my "easter egg" just to prove I was involved ;-)

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Congratulations---break out the cakes!  That certainly must be gratifying to have had a hand in it all.  You probably never imagined you'd be talking about it on the internet 40 years hence; those were early steps along the way that got us here. 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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40 years, wow time flies don't it?

 

I loved programming in those days

Happy Trails,

Mike

JaxCoder.com => PartsBin - An Electronics Component Organizer

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In the link

wink yes

“Everyone knows that debugging is twice as hard as writing a program in the first place. So if you're as clever as you can be when you write it, how will you ever debug it?” - Brian W. Kernighan
“Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.” - Antoine de Saint-Exupery

Last Edited: Mon. Apr 25, 2022 - 10:31 PM
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And Cliff is too modest to post this bit.......cheeky

 

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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5 million + sold in the UK, alone!

 

Wow!

 

Congrats, Cliff!

 

Job well done!

 

JC

 

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Amazing Cliff!

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Excellent Cliff! I like the article you were featured in, it is a worthy tribute to this iconic computer that was a leader in the stable of "home computers" that started so many of us down the road to the computer and IT industries, me included.

 

I still have contact with at least half a dozen of my friends from back as a teenager who had Spectrums or competitors or both even in a back-water country like ours, and went on to greater things building careers in development and the computer and IT world!

 

Hat off to your achievements back then!

Wayne

East London
South Africa

 

  • No, I am not an Electronics Engineer, just a 54 year old hobbyist/enthusiast
  • Yes, I am using Proteus to learn more about circuit design and electronics
  • No, I do not own a licensed copy of Proteus, I am evaluating it legitimately
  • No, I do not believe in software or intellectual property piracy or theft
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Just think what would have been possible with even a simple Mega2560 back then! laugh

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Congrats Cliff.
I remember these amazing machines coming out while I was at uni (and poor) :-).

regards
Greg

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js wrote:

Just think what would have been possible with even a simple Mega2560 back then! laugh

Saying it the other way around....

How on earth did we get such primitive machines to do so much? The answer is probably painstaking, hand-crafting of assembler, and some amazing ideas..... and some fiendishly difficult code to maintain.

 

I do wonder whether what happens at the low level with a processor is a fading/dying skill. With all the great tool kits/libraries around, so much is possible without really understanding the detail. The problem is.... when anything doesn't behave as expected that detailed knowledge about how devices interact, or stacks might have been corrupted, or why buffers ran out ..... always seems to be important in understanding what went wrong.

regards
Greg

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My first was Sinclair ZX81, he is 42 years old now.

 

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You are right that games were doing every last trick to get the performance they needed...

 

The "bug" I mentioned is that the original Spectrum 48K had a single 16K of ROM holding the BASIC. The ROM was almost full but at the very end (0x3F00 and beyond) there were just over 256 bytes of 0xFF which on the surface appeared to be "empty". To add a disk operating system to the Spectrum...

 

 

we actually needed four 16K ROMs that were banked and I needed to add "hooks" into the original 48K code so that the command interpreter (the bit that turned key presses into BASIC tokens) would call out to one of the other ROMs to handle the extra commands I added to allow files to be loaded from disk (and list disk contents and so on). So I spotted the 256+ bytes of "free space" and positioned my "switch to another ROM bank and CALL xxxx" routines there (this is where the really powerful Z80 EX (SP).HL opcode really came into its own!) as it looked like free space.

 

What I hadn't realised at the time is that the way a lot of 48K Spectrum games worked (when they couldn't change the interrupt vector at the start of the 16K ROM) was that they needed an interrupt to alert them of frame flyback so they could synchronise their screen updates to avoid tearing. The way they did this was to switch the Z80 from the Spectrum's default Interrupt mode 1 (where it always vectored into the ROM at 0x0038 at the frame flyback interrupt) into Interrupt mode 2. That's explained here:

 

http://jgmalcolm.com/z80/advance...

 

but basically it jumps to an interrupt handler at an address given by combining whatever happens to be on the data bus at the time of the interrupt (which in Spectrum could be anything from 0x00 to 0xFF) with an indirect lookup from a table who's base address was given by the 8bit I register in the Z80. The 256 bytes of 0xFF in the ROM were at 0x3F00 so the games would set I=0x3F and execute the IM2 opcode and then when an interrupt occurred it would form an address from the table (0xFFFF) which was RAM where the game then put a branch into its flyback handling ISR.

 

Because I put code in the page of 0xFFs not all vectors were 0xFFFF any more and the IM2 interrupt jump would go to the wrong place (usually crashing the game).

 

It's surprising how many of the original 48K Spectrum games used the "IM2 mode trick" ! :-/

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In the early 80's, Spectrums were being sold at a motor accessories store in Jeddah. You know the type... fluffy dice that hung from the mirror. I didn't buy.

Ross McKenzie, Melbourne Australia

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valusoft wrote:
You know the type...

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Fluffiness is missing...

 

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grohote wrote:

My first was Sinclair ZX81, he is 42 years old now.

 

My first computer I ever owned too. yes

Wayne

East London
South Africa

 

  • No, I am not an Electronics Engineer, just a 54 year old hobbyist/enthusiast
  • Yes, I am using Proteus to learn more about circuit design and electronics
  • No, I do not own a licensed copy of Proteus, I am evaluating it legitimately
  • No, I do not believe in software or intellectual property piracy or theft
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grohote wrote:
My first was Sinclair ZX81, he is 42 years old now.

 

Some told that XT(8088) is the first common in South East Asia.

www.tokopedia.com/madagang .Buy and Donated cheap electronics and manuscripts.

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Jeckson wrote:
XT

 

To our young AVR members: XT and then AT are the first IBM models of PC. XT was with monochrome CGA display, and AT with color EGA display.

 

 

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grohote wrote:
XT and then AT are the first IBM models of PC
Sorry to be a pedant but the first IBM PC was actually the 5150. The "XT" was "eXtended Technology" in that it had a better power supply, more expansion slots and they removed the tape drive interface and replaced with a disk drive...

 

https://en.wikipedia.org/wiki/IB...

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You are always welcome! Disc drive: floppy disc big and small... wow, 1.4M, excellent.

 

Somehow, we associate tape drive interface to the nostalgic times of Spectrum and similar... real productivity PC phase do becomes with XT.

 

And, I am a proud owner of a real AT, although it is an exhibition piece in my museum. Works perfectly.

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grohote wrote:
it is an exhibition piece in my museum

I used to have a museum of computers too, then I cleaned out the basement:

 

FF = PI > S.E.T

 

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I used to have a museum of computers too, then I cleaned out the basement

Me too!

 

But I kept my Tandy 2000!

 

It was my first "real" PC, after my ZX80, and my non-commercial 8085 SBC.

 

The T2000 used an 80186, so it ran much faster than the original PC, and had the Double sided double density floppy disk drives, unlike the original IBM PCs.

 

Although Tandy promised me a multi-user, multi-tasking OS for the Tandy2000, they never produced one.

They had a different platform, "for office users", that was mutli-tasking with "dumb" terminals connected to it.

 

JC