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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 3rd May 2020, 6:26 pm   #21
philoupat83
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Default Re: Good review of SC/MP.

ok I inverted protect and load
you are right
I can participate in the plan
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Old 3rd May 2020, 6:28 pm   #22
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Default Re: Good review of SC/MP.

The keyboard is the clever one with so few keys using three shifts to get the full ASCII... Func, Alph 1 and Alph 2 - the INT key and and (Undefined) User key make up the others. I have been trying to work out how they would be read in and wired as they seem to be connected to the data bus and decoded in a memory mapped way.
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Old 3rd May 2020, 6:34 pm   #23
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Default Re: Good review of SC/MP.

My plan was to make a SCRUMPI 1 first (but with the adaption to be able to use an SC/MPII for simpler power) to learn the typical techniques he used - I am sure the same mechanisms were used on the 2 (for which we we need the single PROM image) and then the 3 - which is much more complex and absolutely does need the PROM images somehow... or a rewrite from the descriptions.

I have been beavering away documenting what I can on the 3 as well (as the memory map is likely to be developed from the 2) and have a good working description of the VDU from a purchased journal article although the reprint did not come with the circuit diagram which is referred to... I will keep chasing sources as I think it is important that at least one each of these machines is built and documented.

Note that the SCRUMPI 2 was based on the SC/MPII so only needs a simple 5V power - the Elektor PSU for the SCRUMPI 1 is a good idea
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Old 4th May 2020, 7:28 am   #24
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Default Re: Good review of SC/MP.

yes it is necessary to do the scrumpi 1 to understand the technique implemented
I’ll start creating the schema with the information we have it will be necessary for you to correct it it has obscure points to find
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Old 4th May 2020, 9:04 pm   #25
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Default Re: Good review of SC/MP.

good I’m available again
I just finished 30 visiere in 3d
I have read all the documents I have and I think that IC7-8-9-10 LED drivers are not 74HC07 but SN7407 or 74c07 Hex Buffer open collector ou simple 7404 ?
the plan begins to take shape the base is elektor with NE555 SN7474 and 7400 as written above IC4-3-2
Compute gives a plan Vol3 n4 p11 an Vol2 n11 p6
I note no resistor for the switch pull up
Attached Files
File Type: pdf 7407.pdf (1.25 MB, 69 views)
File Type: pdf Elektor_sch.pdf (386.5 KB, 93 views)
File Type: pdf compute_vol3n4p11.pdf (990.0 KB, 91 views)
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Old 4th May 2020, 9:37 pm   #26
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Default Re: Good review of SC/MP.

Owch that is a shame as I have a stack of 74HC07 I bought to do the job. They will be the CMOS version 74C07 as he specifically says he uses CMOS buffers to reduce the current draw from the LED. I may still use the 74HC07 I have with a resistor inline with the LED - experiments may be needed as I assume that will make the Logic levels inverted... I cannot find a supplier of 74C07 quickly looking at the usual suspects.

Last edited by Timbucus; 4th May 2020 at 9:51 pm.
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Old 4th May 2020, 10:11 pm   #27
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Default Re: Good review of SC/MP.

ok yes 7404 request inversion
Leds are all GND common
what do you think
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Old 4th May 2020, 10:15 pm   #28
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Default Re: Good review of SC/MP.

all the CI are NS so ref DM....
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Old 4th May 2020, 10:58 pm   #29
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Default Re: Good review of SC/MP.

Indeed but, if you look at a lot of the BYWOOD adverts like this ETIOctober1977advert.pdf
he lists a lot of generic 74 series and some specific DM so I think he mixed and matched. As he did not list the 74C07 in any adverts I could find I originally thought of the 74C04 but, could not see how the LED's would not be OFF at Logic 1 which was unintuitive. An Open Drain (or Collector) will be non inverting as the current will flow when the logic level is HIGH.

I could not decide if I should use CMOS 74C00 etc as he lists them but, settled on the 74LS00 as the SC/MP (either) can drive them anyway - and I have a large stock...
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Old 4th May 2020, 11:12 pm   #30
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Default Re: Good review of SC/MP.

Quote:
Originally Posted by philoupat83 View Post
Leds are all GND common
what do you think
I do not think so they would all be tied to +5V so that the Open Drain acts as a low side driver and sinks the current correctly. That is why I think at least a small 330ohm resistor is needed although that may be paranoia as the data sheet says it can handle 25mA and there are none on the SCRUMPI... Please note a real electronics person should check my thinking
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Old 4th May 2020, 11:12 pm   #31
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Default Re: Good review of SC/MP.

a good idea
but it should be noted that 6 gate are used so 6x4=24
number of led 24 (4 CI ) good in PCB

4 gate 74ls00 therefore 6 CI
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Old 4th May 2020, 11:22 pm   #32
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Default Re: Good review of SC/MP.

you are right the pcb shows a gnd rail
which goes left but we see another rail +5V the two passes behind the led it is possible that the risk is taken not to protect the LED
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Old 5th May 2020, 12:29 am   #33
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Default Re: Good review of SC/MP.

Bear in mind 1978 LEDs were not efficient and had larger dies, so may have tolerated relying on the internal resistance of 74 series logic better without overheating.
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Old 5th May 2020, 1:17 pm   #34
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Default Re: Good review of SC/MP.

Hello
a general layout diagram I’m rewriting your part list and
SLOTHIE you are right
I’m thinking in view of the schema that we were very simple in the economic elaboration no rebound for the switches etc
Attached Files
File Type: pdf scrumpi diagramme Model (1).pdf (102.1 KB, 108 views)
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Old 5th May 2020, 3:24 pm   #35
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Default Re: Good review of SC/MP.

test with multisim the schemat Pratical aout 78 is false looks simulation joint
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File Type: pdf NE555.pdf (418.1 KB, 75 views)
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Old 5th May 2020, 9:48 pm   #36
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Default Re: Good review of SC/MP.

an update
a first list share to be checked
Attached Files
File Type: pdf scrumpi diagramme Model (1).pdf (103.0 KB, 86 views)
File Type: txt part list.txt (722 Bytes, 72 views)
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Old 5th May 2020, 10:13 pm   #37
Timbucus
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Default Re: Good review of SC/MP.

Nice diagrams especially the layout getting that and the size accurate will add a lot to how it looks.

I think your circuit is wrong as the SLOW and STEP switches just arrange to either short TRI (PIN 2) to ground or to PIN 6. Thus switches between a slow running 1Hz ASTABLE or a way to provide a clean single pulse on the 7474 to allow a single clock cycle to happen.

I started annotating the diagram from DJD'd Review and this is as far as I got Click image for larger version

Name:	CircuitNotes.jpg
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Old 5th May 2020, 10:20 pm   #38
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Default Re: Good review of SC/MP.

it remains to mix the diagram
a help is necessary to understand the different pin of the sc/mp
Attached Files
File Type: pdf Practical-Electronics-1977-08_SCRUMPI.pdf (1.92 MB, 78 views)
File Type: pdf Elektor_sch.pdf (386.5 KB, 83 views)
File Type: pdf miniscamp_diagrame.pdf (186.6 KB, 75 views)
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Old 5th May 2020, 10:24 pm   #39
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the schemat does not work on multisim c is why I proposed this slow modification is a clock 1 hz for debugging
and step an advance not a multisim confirms it
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Old 5th May 2020, 10:42 pm   #40
Timbucus
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Default Re: Good review of SC/MP.

Also I am also not sure now that IC11 is a 74C04 as you suggest as you can clearly see two patch wires from the marked W and R and I think they snake across the board to use pins 1 and 2 which would be the first Hex inverter on a 7404... Still you can do the same with shorting out the two inputs to a NAND gate so that is also a valid solution and means that IC2 and IC11 - stay in their own areas - the diagram I posted above began to reflect that element of doubt.

Edit - actually that is more likely that IC11 is a 74C00 and the W and R wires running from Pin 1 and 2 on the CPU are going to pin 1 and 2 on IC11 which are the inputs to a NAND gate in that chip... so ignore the above...

Last edited by Timbucus; 5th May 2020 at 11:06 pm.
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