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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 6th Jul 2021, 12:11 pm   #1
Timbucus
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Default Scrumpi 2/3 developments and Scrumpi 4!

For those who followed the original Scrumpi 1 reconstruction thread you know that I wanted to move on via the Scrumpi 2 to eventually the 3.

Several e-mails to The Computer Sheds, who have a Scrumpi 2 have not resulted in any photos of the board and the website I set up had only a few contacts (which I missed for a while due to a mail routing error..). One contact said he had some 2 and 3 material but, as yet has not come back to me with them, either.

I have established that the Case used on the Scrumpi 3 from a recent perusal of some attic found Maplin's magazines was a Vero Type 502 case - part no 21098F - 550x340x120 with a 430x115 panel and Max PCB of 160x220

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One of the most interesting contacts though from the website was an e-mail from Paul Robson who had a few years ago been following a similar reverse engineering path to me, including disassembling the fragments of code in photographs. That resulted in a White room reconstruction of the Scrumpi 3 EPROMs (they function like the described system but, do not preserve the actual known code)... to test this he wrote an emulator as well which he just made public with the EPROM code and I have recently got working on my Linux machine - very creepy playing with a Scrumpi 3...

https://github.com/paulscottrobson/scrumpi3

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Finally an interesting finding from continuing research shows from PE Sep 1978 that JMK planned a SCRUMPI 4 - P.E. probably got the news from the Computer Weekly news update in Jul 1978...

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If you want to play with the emulator the docs are a bit sketchy so here is what I have worked out:

Build
-------

Need to install SDL dev to get it built for Linux

e.g. https://learncgames.com/tutorials/ho...-sdl-on-linux/

just 'make' in the emulator sub dir from the git clone makes an executable.

Operation
-------------

./scrumpi3
F5 to start

Simple program - place XPPC P3 at first byte of user RAM, return to monitor and run
this will do the register and stack dump display seen in one of the photos.

I 7F80 3F
>
G 7F80

Controls
-----------
F1 reset machine (i.e. PC=0000)
F2 home
F5 run emulator
F6 Break back to debug screen - hard breakpoint

TAB - Show

F7 - Step
F8 - Step over
F9 - Breakpoint - set at current displayed address will drop
back to emulator when SC/MP gets to that address

ESC will exit back to OS
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Old 6th Jul 2021, 5:15 pm   #2
Mark1960
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

I was wondering how the scrumpi 4 would handle keyboard and display if it was based on the standard NIBL rom from National Semiconductors, but then reading the article snippets again I noticed the bit about requiring a terminal and possibly using a scrumpi 3 for that. This would seem to mean that the scrumpi 4 was unmodified NIBL which would make it easier to recreate with the same facilities.
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Old 6th Jul 2021, 8:56 pm   #3
Timbucus
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

Yes - they seem to suggest that it would rely on an external terminal - I suppose as it used the standard large NIBL ROM he would have no choice as the Scrumpi 3 architecture would have got in the way but, a basic Scrumpi 3 at £189 with case and PSU was effectively a useful Dumb Terminal already by then in its basic 128 byte model with no RAM expansion etc.

I envision it as a single large PCB a bit like the Nascom or the Triton as he does not mention a rack mount or anything like the ETI S68 used which was originally the first Scrumpi design adapted to the 6800 chip.
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Old 6th Jul 2021, 11:16 pm   #4
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

I think it would have been uncompetitive against the nascom 1 at that price. Though the starter kit for Nascom 1 did not include basic, for the scrumpi 4 @ £150 + scrumpi 3 at £189, I think the Nascom 1 could have been expanded to a much more capable system.
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Old 16th Nov 2021, 10:23 pm   #5
Timbucus
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

I have just updated the Soul of an Old Machine edition on the scrumpi.uk site (mainly on the history pages 8-10) to reflect the above news items and to ensure I capture at least a little bit of the material coming from an e-mail exchange with Mark Phillips.

He contacted me via the site and provided some initial background information and photographs of his Scrumpi II - the fascinating thing is he is the original designer having written and made some suggestions to JMK at Bywood he landed the job while at Birmingham Uni, of doing an improved PCB layout based on his ideas...

Here is the front and back of his board for reference... The address decoding is not what I would have expected - he has more details he hopes to send including a circuit diagram and copies of documentation so I have held off much reverse engineering - what I have done is below.

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Tim

Code:
Chip layout is:
----------------------------
14 13       12 11
      15           10
      16           09
      17 18        08
22 21 19 20        07
                   06
01                 05

02
03		SPARE
04

------------------------------
IC01 is CPU
IC02 is 74C00
IC03 is 74C74
IC04 is NE555

IC05/06 is RAM 2112 expansion 200-2FF
IC07/08 is RAM 2112 expanison 100-1FF
IC09/10 is RAM 2112 base 000-0FF - see below need to work out how PROM start works and memory mapping

IC11-14 are 74C04 LED drivers
IC15/16 are 74C173 I/O latches (as per Microsense ETI Oct 79)

IC17 (74C42) and IC18 (HEF4019) - 2x 16PIN DIL? (V is PIN 9 on IC17, I think P also on this?? pin 12 maybe?)
AD10-8 links to some pins 12-14??
18 seems to have Q on pin 13? Def has the three RAM decodes labeled N,M
Pin 12 I think is base RAM decode...

IC19 and IC20 - 2x 14PIN DIL (both 74C00)
IC21 MM5204 EPROM 512bytes
IC22 is a 74C00 (Only needed with PROM? as shown missing in advert)
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Old 29th Dec 2021, 10:50 pm   #6
Timbucus
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

A quick update to the thread as I have put together a video showing some of the documentation supplied by Mark with photos of the now repaired and working SCRUMPI2 plus a live demo of the SCRUMPI 3 emulator from Paul.

https://youtu.be/iLtzCB6E9aA

If someone wants to see any of the detailed documents while I would out how best to present them let me know.
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Old 29th Dec 2021, 10:53 pm   #7
Timbucus
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

These two are worth putting here - a picture of the repaired board:

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and his hand drawn circuit diagram...

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Old 2nd Jan 2022, 12:18 pm   #8
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

Hi Tim, any chance of a high-res scan of the hand-drawn diagram please?
(I think the forum resizes photos, maybe zip it?)
Ta
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Old 2nd Jan 2022, 1:46 pm   #9
Timbucus
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

Hopefully this is better?
Attached Files
File Type: zip diagram.zip (716.3 KB, 51 views)
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Old 9th Jan 2022, 1:31 pm   #10
Timbucus
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

On a facebook group a SCRUMPI 2 owner (Martin) has surfaced who has the final drawn circuit diagram and a working SCRUMPI 2 - he was happy for the scan and a photo to be shared here as well... As before I have included a ZIP to stop reduction.

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MartinMachine.zip
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Old 11th Jan 2022, 11:31 pm   #11
SiriusHardware
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

Keep it coming Tim - as you know the prospect of actually using these very primitive switch-input, LED output systems doesn't really float my boat, as I used a very similar basic Elektor SC/MP system for real, for several months back in the day. I won't ever do that again.

I'm still interested in them at the technical level though, and your ability to trawl up information about these old systems never ceases to amaze me.
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Old 12th Jan 2022, 1:33 am   #12
Mark1960
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

I think these toggle switch type systems have a special place in history and attempting to program them can give an understanding of the challenges facing the amateur in those early days. There was little chance of a home user having access to anything like the tools we take for granted in our hobby now. It would have required minicomputer access and prom programmers to have anything even close to resembling a modern pc, while the amateur at home would probably have a multimeter and possibly a logic probe. Systems like scrumpi can be bootstrapped using the toggle switches and the single step process can be debugged using a multimeter to monitor signal levels at each step.

The tedious process of programming one of these things prepared a lot of amateurs for the attention to detail and patience for the types of processes they would face in their first jobs in electronics. I’m thinking here of the weeks spent laying out circuit boards with printed symbols and black tape on clear acetate, or updating schematics by scraping the print off ozalid transparencies and marking them up with ink pens.
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Old 12th Jan 2022, 2:04 am   #13
Phil__G
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

Agreed, I really enjoyed building the "switch & LED" Cosmac Elf during lockdown, but after a few days of toggling I just had to make a serial loader for it...
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Old 12th Jan 2022, 9:26 pm   #14
Timbucus
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

Sirius I am amazed what appears in front of my eyes as well - much more to come I am sure... I have been studying the memory decoding differences with the SCRUMPI MKII (to give it its correct. not like MK14, moniker) and the use of the BCD decoder and multiplexer is just off the wall and unexpected.

The changes to the single step are also interesting doing what we discussed (and also the review by DBJ-D) to debounce the single step - not sure yet how it modifies the 555 circuit for that.

I am going to modify my veroboard one to match the design I think at least so I can prove the decoding and ROM start as I THINK that just makes reads to be from the ROM but, writes still to to the RAM but maybe I am not getting it fully as to how they then page out the ROM.

Mark - I totally agree I have learned (or understood fully perhaps) so much more using these different devices around MPU based digital systems - the H8 showed me how Octal was a better bet for 8080 and Z80 for example...

and Phil you are correct switches and hex pads are handy for showing off the way it used to be but cross assemblers and serial connections should be the first thing you write
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Old 16th Feb 2022, 1:15 pm   #15
martint123
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

Tim, a request please. I've lost my Facebook account, email and phone number changed profile deleted. grrrrrrr. Could you give me a pointer to the FB post you spotted for me so I can try to work backwards to find something?

Martin.
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Old 16th Feb 2022, 9:22 pm   #16
Timbucus
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Default Re: Scrumpi 2/3 developments and Scrumpi 4!

Martin welcome to the forum- I think the original post in Vintage Computers has been deleted as I can no longer click on it in the activity log - I assume you mean the one where the picture of the SCRUMPI II above was posted? If it was something else then I may have also posted it here on the forum as there are several threads on SCRUMPI so it may have been among those.

As a new user your posts may take some time to appear here as they are subject to moderation for the first 10 or so.

Last edited by Timbucus; 16th Feb 2022 at 9:34 pm.
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