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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 17th Jul 2020, 6:36 pm   #401
philoupat83
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Default Re: Recreating the Bywood Scrumpi

greetings to all
Happy for you. Play well with
for the power supply I opted for a transformer.
2x12v 10VA to generate +5v with a 7805 to3 -12v with a 7912 -7v and -9v with two lm337 adjustable.
I finish the box in 3d
I'm thinking of interfacing with an arduino to program scrumpi. I'm a little lazy.
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Old 17th Jul 2020, 10:09 pm   #402
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my power suply for scrumpi
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Old 18th Jul 2020, 11:14 am   #403
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Default Re: Recreating the Bywood Scrumpi

hello
for the continuation of the project I build a programmer of mm5204q the Eprom used in scrumpi 2.
I can't understand the use of four circuits for ram and rom addressing I suppose a 74c42 and a 74c00 maybe a 74c04.
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Old 18th Jul 2020, 3:10 pm   #404
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Default Re: Recreating the Bywood Scrumpi

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Originally Posted by philoupat83 View Post
hello
for the continuation of the project I build a programmer of mm5204q the Eprom used in scrumpi 2.
I can't understand the use of four circuits for ram and rom addressing I suppose a 74c42 and a 74c00 maybe a 74c04.
As we do not know the memory map it is also harder. I notice that the switch allows you to change from RAM to EPROM for boot so it must switch what is in the lower 256 or 512 memory area. The EPROM is 512 bytes and the basic Memory is 256, you can add another two pairs of Chips for an extra 256 or 512 so to allow all the installed memory to be used (and the expansion bus) it must do full decoding and allow the first 256 bytes of RAM to be moved out of the way of the EPROM.

If I was a betting man I would guess:

000 : 256 RAM or Lower EPROM
100 : 256 Upper EPROM
200 : 256 RAM Expansion
300 : 256 RAM Expansion
400 : 256 Position for switched out RAM if not EPROM?
500 256 - unused / would be EPROM upper if not switched low
600 256 - Latch Chip 1
700 256 - optional Latch Chip 2 (depending on wiring for seperate in/out)
800 > Remaining 2K - Expansion BUS

This allows a simple full 512 decode exchange for RAM and EPROM and each Latch Chip to be used together as 8 bit or separate as IN and OUT. - The SCRUMPI 1 interfacing manual page refers to needed additional gates to achieve that - maybe they were included.

I am hoping Slothie will start thinking about this scheme - he seems to have a lot of bright ideas on decoding schemes...

Your possible 74C00 to the right of the Prom is also interesting - I had wondered if it was an external clock circuit of some kind but, that is empty on the Austin model and present in the picture from the advert with a 512byte PROM so maybe the SWITCH out RAM option is only available when that is present?
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Old 18th Jul 2020, 3:12 pm   #405
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Default Re: Recreating the Bywood Scrumpi

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my power suply for scrumpi
Very posh - I wish I could get my 3D printer to work - it has a fault on the Z axis and I am now stumped. Maybe I will have time to look at it again this weekend.
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Old 18th Jul 2020, 4:07 pm   #406
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I am hoping Slothie will start thinking about this scheme - he seems to have a lot of bright ideas on decoding schemes...
I will certainly think about this. I should have my laptop by midweek so that will help!
Switching the RAM in and out isnt so hard, remapping it is trickier but not impossible. Back in '79 wasting 256 bytes if ROM is switched in would be unheard of!
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Old 18th Jul 2020, 6:00 pm   #407
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Default Re: Recreating the Bywood Scrumpi

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Quote:
Originally Posted by Timbucus View Post

I am hoping Slothie will start thinking about this scheme - he seems to have a lot of bright ideas on decoding schemes...
I will certainly think about this. I should have my laptop by midweek so that will help!
Switching the RAM in and out isnt so hard, remapping it is trickier but not impossible. Back in '79 wasting 256 bytes if ROM is switched in would be unheard of!
Exactly why I thought it would be switched into another place for use.
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Old 18th Jul 2020, 6:40 pm   #408
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Is it possible that there used a 74138 3 to 8 decoder or similar? Then it would be easy to switch the 256 byte blocks around. I'll need to reread the docs you put up here before commenting further.
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Old 18th Jul 2020, 7:22 pm   #409
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yes maybe a 74c138 as for the Australian scamp or elektor
but the BYWOOD ad doesn't give this circuit that's why I thought of 74c42 for the activation of the ram rom blocks.
TIM here is why I love 3d printing I changed the front panel to white it's better
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Old 20th Jul 2020, 6:54 pm   #410
Karen O
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Default Re: Recreating the Bywood Scrumpi

Question: how much current does the SC/MP-I draw from the -7V rail?

Often negative supply rails serve simply to bias the substrate and draw very little current, but I suspect PMOS actually uses the negative rail for powering logic...?
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Old 20th Jul 2020, 7:24 pm   #411
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Originally Posted by Karen O View Post
Question: how much current does the SC/MP-I draw from the -7V rail?

Often negative supply rails serve simply to bias the substrate and draw very little current, but I suspect PMOS actually uses the negative rail for powering logic...?
The SC/MP passes all its current through the -7v rail as it doesn't have a 0v pin. Presumably it generates this 0v level internally.
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Old 20th Jul 2020, 9:04 pm   #412
Karen O
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So, it's really a 12V part with the logic levels huddled at the top end
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Old 20th Jul 2020, 9:07 pm   #413
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hello
Yeah, the sc/mp doesn't have 0v. I'm going to do some measurements for Karen.
to come back to scrumpi3 I think that the approach of the circuit seems to be an INS8060 a INS 8154 an AY-5-1013 and although the very meager documentation mentions a vdu based on 8675bwf I think it's wrong rather a DM8678 bwf or cab (what difference ?)
two eprom mm5204q one for the monitor and one for the user. too bad there's no bywood schematic that says this is not necessary for the kit.
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Old 20th Jul 2020, 9:09 pm   #414
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see
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Old 20th Jul 2020, 9:14 pm   #415
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Tim, do you think the TRITON is a simplified scumpi? Watch the chess TV game.
see ETI-1978-10-78.
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Old 20th Jul 2020, 9:16 pm   #416
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see
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Old 21st Jul 2020, 3:17 pm   #417
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Default Re: Recreating the Bywood Scrumpi

The Data Sheet for the SC/MP 1 is attached it says IGG is 135mA Max.

Phil you are correct on the Chips and the Video Part it must be DM8678BWF (this was in the notes I posted earlier as it is mentioned in the Elsevier article) out of interest the others in the family are:

DM8678BWF 7x9 Upper Case Block Letters - SCRUMPI 3
DM8678CAE 7x9 Shifted Lower Case Block
DM8678CAB 5x7 Upper Case Block Letters - Original MK14 VDU
DM8678CAH 5x7 Shifted Lower Case Block
DM8678CAD 7x9 Kata Kana
DM8678BTK 7x9 Upper Case Script Letters
DM8678CAS 7x9 IBM 3741 Selectric

The Triton is an 8080 machine described in the next few issues of ETI and not related to SCRUMPI at all.

The TOLINKA Chess game is an interesting SC/MP II item used as a recorder for two humans Chess games to cassette - it could not actually play itself but, sadly there is no listing of the code I can find.
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Old 21st Jul 2020, 4:06 pm   #418
Karen O
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Default Re: Recreating the Bywood Scrumpi

I'm going to place an order for the parts needed for my Scrumpi. I can probably rustle up vintage-looking parts, but the IC sockets are going to have to be modern.

Were 'turned pin' IC sockets available mid-70s?

I can't remember

Only the best for my Scrumpi
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Old 21st Jul 2020, 4:41 pm   #419
Timbucus
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Funny enough I have just been seeing what I still had missing for mine now I finally managed to get a full set of red switches and it was IC sockets I didn't have (14 pin!!!! arghh). I have just ordered some standard ones. I do have turned pin on my CPU on the MK14 repros for ease of swapping out the chip but, have ordered some plain ones for this as like you I am not certain I remember seeing turned pin much back then.

The 3mm LED's with built in resistance from the link that Phil posted arrived very quickly from Germany. I think my parts list still says 5mm but, Mike says they are 3mm and you need that small for the spacing.
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Old 21st Jul 2020, 5:24 pm   #420
Karen O
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Tah for the heads up on the LEDs TimB.
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