1st Sep 2020, 10:51 pm | #461 |
Octode
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Re: Recreating the Bywood Scrumpi
On a related subject of modern boards that use SCRUMPI type ideas (if not the SC/MP instructions) I was interested to come across this Digirule2 which is the subject of a currently running Kickstarter
I have backed one as I might tackle converting KarenO's SC/MP work for the MK14 to it to make a small portable SCRUMPI! I need a project to learn about the PIC... In the comments at the bottom of BRAD's page are some photos of through hole board versions that reminded me strongly of the SCRUMPI... ************************CMCCV4NG/IMG-0999.jpg |
2nd Sep 2020, 9:36 pm | #462 |
Octode
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Re: Recreating the Bywood Scrumpi
A similar binary programmed device we have discussed in this thread I think at some point was the OSI300 from November 1975.
Well I just came across a video showing one operating: https://www.youtube.com/watch?v=3gEiJiN7TiM it is 6502 obviously as we discovered but, seeing it in action is interesting and shows that the SCRUMPI was seriously much better - twice as much memory and good quality switches for half the price... $99 would have been around £147 as opposed to the SCRUMPI launch price of only £64.81 - although it was a year later in December 1976. |
4th Sep 2020, 4:57 pm | #463 |
Dekatron
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Re: Recreating the Bywood Scrumpi
Nice video about OSI - I can remember Ohio Scientific but never knew they'd offered such a basic trainer system.
Now all we need is something similar for Acorn computers, no doubt entitled 'From Little Acorns..' and starting with the System 1. I spent a while looking around the Digirule stuff but one thing I could not see was whether it used the instruction set of an existing uP family or whether it has its own 'custom' instruction set. Did you manage to work that out? I see it's been fully backed, anyway. From the logo on the main IC (Microchip?) I would say the underlying uP is a PIC. |
4th Sep 2020, 5:27 pm | #464 |
Octode
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Re: Recreating the Bywood Scrumpi
The Digirule is indeed a PIC but, and it does use its own made up instruction set for an imaginary 8 bit uP that is implemented on it - but, as it has a programming interface I was thinking of knocking up some firmware to convert it to an SC/MP! If you look at the picture of the back of the rule on the site they are listed there on the site https://bradsprojects.com/digirule2/
Did you know that the System 1 used 8154 and 571 chips because they were on the MK14 and "around" you can see the interview with Sophie Wilson here: http://speleotrove.com/acorn/acornHistory.html This also has the snippet in the table that the MK14 was the architect of its own doom as it was used with its programmer to blow the first PROM's! |
4th Sep 2020, 5:43 pm | #465 |
Dekatron
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Re: Recreating the Bywood Scrumpi
I dare say C.C. had already been thinking about this before departing from SOC and no doubt 'borrowed' some components from work, as one does, for 'evaluation'.
I don't know the S1, does it use the 8154 as part of its main circuit? If so that decision all those years ago will have made it doubly difficult to make an exact System 1 replica now, with both 74S571s and INS8154s being increasingly difficult to get. |
4th Sep 2020, 5:51 pm | #466 |
Octode
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Re: Recreating the Bywood Scrumpi
It uses it only as IO and extra RAM I think, it is a system I have not looked at that much but, the diagrams are here https://www.4corn.co.uk/articles/diagrams/.
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4th Sep 2020, 6:09 pm | #467 |
Dekatron
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Re: Recreating the Bywood Scrumpi
Actually, looking at the main diagram it appears to use TWO 8154s, one 'optional' in the same sense as the one on the MK14, but the other is the basis of the interface to the keypad / display and cassette interface.
I see they did, however, have the sense to make all the bus signals available at the expansion connector as standard, something no original MK14 ever managed. |
4th Sep 2020, 8:37 pm | #468 |
Octode
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Re: Recreating the Bywood Scrumpi
The plan was that the "Acorn 1" was a CPU card to be used in a rack-type system, the keyboard/display/tape card was an add-on to turn the CPU card into a stand alone system. My school bought the Acorn-1 with keyboard/display assembled into a card sandwich and I spent many happy hours programming it for parents evening displays etc I remember how much more "powerful" it felt than the MK14 (Which I had also had access to because one of my teachers let us use his) but I was also aware it was a more expensive beast than the MK14.
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4th Sep 2020, 10:25 pm | #469 |
Heptode
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Re: Recreating the Bywood Scrumpi
I too had an Acorn Sandwich, but that's long gone now. I also had two unpopulated System 1 PCBs which I sold on eBay about 10 years ago, for £50 each !.
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4th Sep 2020, 10:59 pm | #470 |
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Re: Recreating the Bywood Scrumpi
trev-ham has listed his repro System 1 PCB's at the moment on the Bay - he says that is the last ever batch and there are two sets left if anyone wants to secure some.
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8th Sep 2020, 9:36 pm | #471 |
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Re: Recreating the Bywood Scrumpi
Putting this thread a bit back on track (I will create a separate thread to continue any Acorn System 1 posts) worth looking at this post on the PIC14 thread for people coming later for Phil G's PW built SCAMP system which bears a striking similarity of design to the SCRUMPI. The April 1980 MicroBUS was presented by DJD who of course reviewed the SCRUMPI several years before but, it was not his design.
https://www.vintage-radio.net/forum/...3&postcount=58 |
26th Sep 2020, 10:52 pm | #472 |
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Re: Recreating the Bywood Scrumpi
I have also just realised that this machine of Karen's in the homebrew section is also worth cross linking here for the SCRUMPI like minimal approach... and clever use of the IRQ line as an built in input for RX data as the Z80 is not as flexible as the SC/MP on IO without supporting chips.
https://vintage-radio.net/forum/show...92&postcount=1 |
27th Sep 2020, 8:44 am | #473 |
Octode
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Re: Recreating the Bywood Scrumpi
Thats certainly an extremely novel approach to serial I/O Just goes to show the genius (or is that insanity?) Karen posesses. I love how neat and complete the resulting device is, if I were to have made it it wouldn't have been so well finished.
Hmmm.. 32k of program entered through toggle switches - that surely is a "Iron (wo)man" challenge! |
27th Sep 2020, 9:12 am | #474 | |
Octode
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Re: Recreating the Bywood Scrumpi
Quote:
Oblique reference to early days Big Iron? Indeed too much, hence only 8 address lines as you would only expect to put in the bootstrap - even entering her echo.asm at 85 bytes was very hard - especially when I realised I had not stepped all the way to 0x40 to enter most of it. I have since written a shorter stage 1 bootstrap of only 58 bytes for it (infinite improbability factor reducing as we speak) based on my SCRUMPI one. |
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27th Sep 2020, 9:31 am | #475 |
Octode
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Re: Recreating the Bywood Scrumpi
Well I've plenty to keep myself busy when I move lol In storage I have a box full of ICs for retro computers, Z80 CPU/SIO/PIO/CTC/DMA, 6809, 6309, 6502, 65816, 6800, EPROMs, RAMS, CTCs, IO Chips like 6521 and 6522, Sound chips, parts to build more MK14s (If anyone can make a replica INS8154 that will be nice!) and now I have PCBs for an Acorn1, MK14s, ZX80.81, SCRUMPI.... I also have a number of machines to restore.
BUT I still love these old minimal computers and I think they make excellent training aids when you're trying to work out how the computer works at a hardware level. You can learn so much from looking at a 3 instruction program wiggling the wires that hours of manual reading cannot teach. Thats why I think the SCRUMPI may be the first on the list (just to get me warmed up for the PROM programmer Sirius!) because its not going to take too long. I might graft a different memory chip on if I can't get hold of the right ones, but thats all part of the fun. |
17th Oct 2020, 7:54 pm | #476 |
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Re: Recreating the Bywood Scrumpi
I found a couple of interesting links while looking for something else.
Reference to an scrumpi 3 publication by John Miller-Kirkpatrick, though it seems to require purchase. https://www.sciencedirect.com/scienc...26271478911678 And online library link for “How to design, build & program your own working computer system”. https://archive.org/stream/howtodesi...Kirkpatrick+sc |
18th Oct 2020, 11:42 am | #477 | |
Octode
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Re: Recreating the Bywood Scrumpi
Quote:
The machine in the book is similar using binary entry of data only and address entry automatically driven by the CPU. It happened to come up on Amazon last year... It's a good read |
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