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Old 13th May 2024, 9:24 pm   #1
agardiner
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Default Acorn System 1

Back when I was a teenager I always wanted to mess around with a micro trainer but it never happened.

So, I have just built an Acorn system 1 using the excellent PCB from Acorn Replicas.

All working and now started reading the manual and playing with it.

Just wondered if anyone else has one of these (or an original) and what they think of it?

Regards,

Adrian.
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Old 14th May 2024, 4:35 am   #2
TonyDuell
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Default Re: Acorn System 1

Never had a System 1. Just a couple of System 4's (the 2 card cages in a 6U rack cabinet, pair of floppy drives in the top cage). One has the 6502 CPU board, 40 column VDU and econet. The other has the 6809 CPU board and 80 column VDU.
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Old 14th May 2024, 7:54 am   #3
SiriusHardware
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Default Re: Acorn System 1

I've never laid hands on a System 1 or used one so I'd be more interested to know what you actually think of it. In a sense the System 1 was the MK14 'done right', with a more mainstream microprocessor and the majority of the system bus signals brought out to a Eurocard style connector right from the start - in fact I understand it was in development while Chris Curry was still working for Science Of Cambridge. Legend has it that the optional BPROM programmer of the MK14 was used to program the PROM code for the first System 1.

Do you have an assembler for 6502? Writing code for these old systems is so much easier now that we can write the code off-machine on more modern systems, an option we didn't have when machines like the System 1 were our only 'computer'.

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Old 14th May 2024, 9:39 am   #4
SiriusHardware
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Default Re: Acorn System 1

I've just had a look through the user manual here, for the first time:-

https://hobbyelectronics.net/wp-cont...UserManual.pdf

I have to say that if this was my first encounter with any programmable 'thing' that manual would have looked quite daunting - the MK14 manual is often criticised for being quite a poor guide for the absolute beginner, and so it is, but the System 1 manual is slightly worse IMO.

Since the system has a matrix keypad it looks as though it would lend itself quite well to an adapted version of the MK14 Pi-uploader which 'types' the program code into the machine via optocouplers connected to the row and column lines of the keypad matrix.

The use of not just one, but two nearly unobtainable INS8154 I/O RAM ICs and two equally exotic PROMs must make these replicas pretty expensive to put together nowadays.
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Old 14th May 2024, 9:45 am   #5
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Default Re: Acorn System 1

I did use a System 1, although I don't think it was actually called System 1 till later. This, along with a Softy, was the development platform for a device used to measure the height of a stack of cardboard sheets, then calculate the number of sheets. The height was measured using a Polaroid ultrasonic gauge. It was my first microcontroller project in the industrial world.

The project needed a microcontroller, and the only two I was even remotely familiar with were the 8060 and the 6502

The Acorn was much better built than the MK14, and had a somewhat better keyboard, so I chose that. The biggest difference was the ease of assembly programming and hardware design by using the 6502 instead of 8060, with proper subroutines and a 64K address space.

The project was a success, but it was the both the first and last microcontroller project for me in the industrial realm. After that my work was on Apple ][ machines.

The Acorn + Softy development platform was good in the day, but today, as Siruis says, it is so much easier to develop the code on a PC.

So I have fond memories of the Acorn, but I would not call it a micro trainer. A trainer would have some I/O for lamps and switches, and firmware specially developed for the task.

However, today there are hundreds of pages on the Internet with 6502 code and projects, so you should find some good ideas for what to do with your replica.

Cheers,

Buzby
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Old 14th May 2024, 2:31 pm   #6
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Default Re: Acorn System 1

Quote:
Originally Posted by SiriusHardware View Post
I have to say that if this was my first encounter with any programmable 'thing' that manual would have looked quite daunting - the MK14 manual is often criticised for being quite a poor guide for the absolute beginner, and so it is, but the System 1 manual is slightly worse IMO.
..................
The use of not just one, but two nearly unobtainable INS8154 I/O RAM ICs and two equally exotic PROMs must make these replicas pretty expensive to put together nowadays.
Yes; I bought the PCB, PROM and INS8154 from Acorn Replicas, and sourced the rest of the parts from various suppliers. In the end, it cost around the same as buying a complete kit. The manual is a little daunting, but I am following it carefully and it is starting to make sense.
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Old 14th May 2024, 2:36 pm   #7
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Default Re: Acorn System 1

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Originally Posted by SiriusHardware View Post
I've never laid hands on a System 1 or used one so I'd be more interested to know what you actually think of it. In a sense the System 1 was the MK14 'done right', with a more mainstream microprocessor and the majority of the system bus signals brought out to a Eurocard style connector right from the start - in fact I understand it was in development while Chris Curry was still working for Science Of Cambridge. Legend has it that the optional BPROM programmer of the MK14 was used to program the PROM code for the first System 1.

Do you have an assembler for 6502? Writing code for these old systems is so much easier now that we can write the code off-machine on more modern systems, an option we didn't have when machines like the System 1 were our only 'computer'.
So far, I really like it. Back in 'the day', I played with a ZX81 and Spectrum before moving onto better machines. Like most teenagers though I mainly played games, and only dabbled with Basic a bit. Now, I am interested in going back to just before these machines and actually learning something. The system 1 appealed over the Sinclair effort for 3 reasons...

1) Availability of the PCB and various parts including a pre-programmed ROM, as I don't want to have to program my own yet.
2) Availability of information around the 6502 which overall seems a better CPU than many others of the period.
3) The ability to further expand the system 1.

My plans are to get to grips with it, enjoy learning basic programming, and then build it out with a VDU and keyboard expansions, eventually perhaps adding a BASIC rom. Whether I will succeed is another matter!
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Old 14th May 2024, 2:51 pm   #8
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Default Re: Acorn System 1

You seem to be the pioneer at the moment - I know at least one person here did intend to build up one of those replicas but never got around to it, so if you'd like to keep us updated here with your progress and anything you do with it, please do, we'll all be very interested to see how you get on.

Certainly the CPU is a 'sensible' historic CPU to start off on - As Buzby alluded to earlier, like the Z80, 6809 and other well-rounded processors of the time it has a Call / Return method of implementing calls to subroutines and returning from them, virtually the exact equivalent of GOSUB and RETURN in BASIC which means you can write a block of useful code once and call it from wherever it is needed.

Looking forward to seeing further progress - maybe if there's anyone else hovering over an unpopulated replica or non-working original System 1, this may be the impetus they need to get things moving.
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Old 14th May 2024, 3:18 pm   #9
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Default Re: Acorn System 1

No problem at all. Progress may be slow due to work commitments, but I will be sure to update this thread as things progress.

Certainly for anyone considering one of these, the quality of the PCB is excellent and the actual build was really nice and fun. I didn't bother putting the logic chips in sockets because generally I prefer the neatness of ICs directly on the board. I did use sockets though for the rare INS IC, the ROM, RAM and CPU ICs. This was primarily so I could substitute in future more than anything else. I opted to leave out the 7805 and power the unit from a powerbank.

One part which was not easy to find was a 1MHz crystal. These seem to be pretty rare now!
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Old 14th May 2024, 4:25 pm   #10
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Default Re: Acorn System 1

Quote:
Originally Posted by agardiner View Post
One part which was not easy to find was a 1MHz crystal. These seem to be pretty rare now!
They're not hard to find but expensive:
https://www.digikey.co.uk/en/product...-13-1XH/827491
https://www.mouser.co.uk/ProductDeta...nBIcszhg%3D%3D
for my Cosmac Elf I wanted an authentic chunky HC33U and bought a couple of these: https://www.ebay.co.uk/itm/144221266564
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Old 14th May 2024, 4:55 pm   #11
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Default Re: Acorn System 1

I have compiled the full kit of parts to build one but, I keep thinking it looks so nice as a kit I cannot bring myself to build it. I have done the same (compiled a kit) with an MK14 as well - although in that case I do have several built ones. The kits sort of provide a useful extra 'exhibit' for certain vintage shows - and that's my excuse. I did a lot of 6502 on the Atari and CBM64 so had less of an interest in learning that chip and why I went down the INS8060/MK14 route for my alternate history.

I will be following your progress with interest though. Especially if you adapt the opto isolated type in loader, that would be a must for me after the first weeks of short programs.
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Old 14th May 2024, 5:35 pm   #12
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Default Re: Acorn System 1

I would be interested to know:

-After reset or power-on, the key presses required to go to a specific address, then change to data entry mode and then enter a few successive bytes of data.

-The key presses required to get out of data entry mode and into address entry mode, enter a new address, and then go back into data entry mode.

-The key presses required to get out of data entry mode, enter an execution address and run from the address entered.

DavidMS's Pi Pico version of the opto-loader could also be modified for this as well. Thread here:-

https://www.vintage-radio.net/forum/...d.php?t=197465

A keypad injection loader need not necessarily utilise optos, there is always the option to use back-to-back 4051 ICs to connect rows to columns - the 3V3 outputs from a Pi Pico could probably successfully drive the 7 logic inputs required to operate a pair of those.

Does the System 1 keypad PCB have a connection / connector intended for an external / off board keypad?
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Old 14th May 2024, 5:42 pm   #13
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Default Re: Acorn System 1

Quote:
I have compiled the full kit of parts to build one but, I keep thinking it looks so nice as a kit I cannot bring myself to build it.
Maybe your solution is to buy another set of PCBs, populate those with all of the necessary low cost / passive parts plus sockets for the expensive ICs and put the socketed parts into that when you want to play, and take them out and put them back into the 'kit' with the unpopulated PCBs and unfitted passive components when you just want to display it as a 'kit'.
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Old 14th May 2024, 6:57 pm   #14
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Default Re: Acorn System 1

I don't have one, so I got to wondering if there is a PC based emulator for the System 1, and of course there is:-

https://speleotrove.com/acorn/index.html

I haven't gone so far as to download and try it yet - the emulator may itself require a relatively historic machine to run on as it mentions Windows 98 - not a problem for me as I still have a '98 machine.

One of the more intriguing extra features seems to be that it can save the memory content out as MIDI data - will have to look further into why that approach was taken.
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Old 14th May 2024, 8:12 pm   #15
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Default Re: Acorn System 1

Hi Adrian / all,

Hopefully you've found that Chris Oddy (who uses the 'Acorn Replicas' brand on his PCB's / for his eBay shop, plus is on this forum), has his own website https://theoddys.com
Where there is probably the largest amount of information on the Acorn System etc. on any one website. As well as now having a lot of info on associated systems like the SoC MK14 and the early Softy EPROM Programmers.

The original Acorn 'System 1' is actually comprised of two PCB's:
a. The 6502 CPU board - Which is also used in the System 2, 3 & 4 Eurocards Rack-based systems
b. The top Keyboard / Display + Cassette interface board.
- With these linked together with a ribbon cable, so the 64way 2 row DIN 41612 or the 20way full (ASCII-encoded) keyboard connectors are not required to be fitted to the 6502 CPU board, or a backplane required for this 'minimal system'

Chris has done a replica of the System 1/2/3/4 6502 CPU board, but I don't think he has done a true-replica of the 'System-1' Only Keyboard/Display+Cassette Interface board as he was primarily interested in rack-based system 2/3/4's having original started out building a System 2 back when they were originally launched.
And Trevor Hamlett had already done a replica of both 'System 1' boards - The top Keyboard / Display + Cassette Interface board (+ also the 6502 CPU board and also the MK14 etc.). Chris had helped Trevor debug some of the Acorn Replica boards, and Trevor had sold the bare boards on eBay for a while - But doesn't appear to any more.

More-recently, the Cambridge Centre for Computing History asked Chris if he could make some replica Acorn System 1's for them, so that they could run classes on programming these without relying on old originals.
But due to difficulties / cost of getting some of the original keyboard / display etc parts, Chris decided to do a 'System 1 Trainer' version on a single 'MK14 form-factor' PCB.
But this has also been designed to be cut 'in-half' so that the rear part can be fitted into a rack to make a System 2, once the rear + front-panel connectors have been fitted.

And I presume this is the version that Adrian has, which has dispensed with the Bipolar PROM sockets, just leaving a DIL24 EPROM socket, and also changed the two 2114's 1KB SRAM to a larger single 6116 2KB SRAM.
Plus the additional INS8154 PIA has gone (although the 64way DIN 41612 connector is still present, for use with a backplane rack).
There is still one INS8154 required, as at the time Chris was still able to buy these from a source (in Australia!). But it may be possible to use a 6520 / 6522, with pin-out conversion, to replace as IIRC this has been tried by other Acorn System people after they found the required registers are the same, so didn't need to mod the firmware.

I have built-up one of these 'updated new-design' PCB's I got from Chris myself. It does use a smaller HC49 1MHz Crystal, that isn't very common in this case (The original was a larger HC33) and only seems to be sold by Digikey . Mouser at a rather-high £6+
I did find found I had a few (custom-spec made?) 1MHz HC49/4H crystals, and had fitted one to mine. This did work, but it seems Acorn used a rather odd oscillator circuit that was designed to operate at Series-resonance so a more-common parallel-resonant one was a bit off-frequency. And I had been looking at mod-ing mine a bit to use the more-standard parallel resonant pierce?) oscillator designs in the original 6502 datasheet.

I do also have an original Acorn System (1/2/3/4) 6502 CPU board, that I have re-built after someone had stripped it of most of the main parts, which now works. So I now need to build-up a rack around one of Chris's backplane PCB replica's, to use this.
- As well as make a suitable full-size ASCII-encoded Keyboard (that the original used anther hard / expensive to obtain AY-3-xxxx Keyboard encoder IC. But need to swap to one that suits whatever Keyboard matrix keyboard I end-up using / May be able to convert a standard PC PS/2 keyboard, with the aid of a microcontroller - as has been done with many Nascom systems).

Owen
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Old 14th May 2024, 8:27 pm   #16
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Default Re: Acorn System 1

Thanks Owen; you are of course correct in that it is one of Chris's PCB's that I used to build my system. And I am aware of his website which as you say is excellent.

For anyone else contemplating building one, it is also worth knowing that Chris is very approachable and helpful. He doesn't plan to produce any more complete kits when he runs out, but the PCBs are still available from him.
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Old 14th May 2024, 8:27 pm   #17
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Default Re: Acorn System 1

Quote:
Originally Posted by SiriusHardware View Post
I would be interested to know:
>>

Does the System 1 keypad PCB have a connection / connector intended for an external / off board keypad?

Well the connections from the (always required / only one on Chris's Acorn System 1 Trainer) INS8154 on the 6502 CPU board are what's used to scan the keyboard (as well as output to the display).
And on an Acorn system 1 / on Chris's Acorn System 1 Trainer there is a space for a 20way connector (Normally designed to fit a full-size keyboard, and display is dispensed with for a VDU card on a system 2/3/4) to get at these.
But you do also have the (quite slow?) Cassette Interface on these as standard.

However, I don't know if there was ever much software created for the System 1 - I imagine most upgraded to the ore versatile System 2 etc. where you could had a full Alpha-numeric QWERTY keyboard (something the MK14 never quite got), as well as a proper VDU output.
And the System 2 / 3 may be able to run Acorn Atom software.
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Old 14th May 2024, 8:31 pm   #18
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Default Re: Acorn System 1

Quote:
Originally Posted by SiriusHardware View Post
>>

The use of not just one, but two nearly unobtainable INS8154 I/O RAM ICs and two equally exotic PROMs must make these replicas pretty expensive to put together nowadays.
Well only one of the INS8154's is actually normally required (and I think a 6520 / 6522 may be usable without software changes - just a pinout adaptor, that I recall seeing someone had done)

And you can just fit an EPROM into the DIL24 socket instead of the two Bipolar PROM's (although at least Tesla one's are still currently available and can be programmed by a few of us / bought ready-programmed)
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Old 14th May 2024, 8:37 pm   #19
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Default Re: Acorn System 1

Quote:
Originally Posted by agardiner View Post
>>
>>
The system 1 appealed over the Sinclair effort for 3 reasons...

1) Availability of the PCB and various parts including a pre-programmed ROM, as I don't want to have to program my own yet.
Well both of these are also available for the MK14, from a number of people - Including from 'Acorn Replicas' (on his website at least) - if you did ever fancy going back in time a bit further (ChrisOddy did end-up doing this, as a result of his work on the Acorn System originally and has since built-up a good archive of things MK14-related as well)
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Old 14th May 2024, 8:45 pm   #20
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Default Re: Acorn System 1

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Thanks Owen; you are of course correct in that it is one of Chris's PCB's that I used to build my system. And I am aware of his website which as you say is excellent.

For anyone else contemplating building one, it is also worth knowing that Chris is very approachable and helpful. He doesn't plan to produce any more complete kits when he runs out, but the PCBs are still available from him.
Yes, Chris told me (we both work in the same Electronics Lab, and he'll probably been on here again in a few days) that due to INS8154 availability at sensible prices its not really practical to provide kits with these in any more.
I think the Acorn System 1 Trainer was only really originally intended for the CfCH, but there had been some interest from others who also wanted to have a System 1 like computer - at rather less than £1k cost originals now go for!
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