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Thread: National Semiconductor SC/MP Introkit

  1. #41
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    Thanks for that clarification. I think auto correct got the better of that sentence! I did type 'unpowered'.

    I also think I have spotted a broken yellow wire wrap. I will post later.

    Dave

  2. #42
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    This thread has gone quiet for a bit so I thought I would 'bump' it.

    Are people waiting for me?

    Dave

  3. #43

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    Yes!

    Post #41, you mentioned you thought you had spotted a broken wire in the photos, so we're all ears / eyes.

    I'm not sure that Gabriel has the same interest in this as we obviously do, though, unless he is still handicapped by new user moderation. Only making a few more posts can fix that.

  4. #44
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    It may be that the wire that I thought was adrift is wired to the other white 24-pin socket?

    Either way round, the white sockets look to have their pins largely wired in parallel (guessing except for the chip selects) whereas the black socket is wired differently.

    Just wondering whether the black 24-pin socket was used as an expansion connector to other things (as the edge connector appears only to be used for power). Either that, or a different type of ROM/EPROM to what is supposed to be fitted into the white sockets?

    I can see a collection of 7 off yellow wires going to the white socket near the edge of the board. It is unusual to have 7 of anything, and I see that the wires all 'cross ove'r each other as they pass from the black socket to the white socket. The exception is one odd yellow wire which doesn't.

    My guess is that the eight yellow wires are either the data bus or the lower 8-bits of the address bus. It should be fairly straightforwards with a multimeter (knowing the pinout of the SC/MP CPU) to find out what is an address line and what is a data line.

    Yes, Gabriel still only has 8 posts...

    Dave

  5. #45
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    Just been looking up the data sheet.

    With a capacitor of 680 pF fitted instead of a 1 MHz crystal, the clock should be approximately 700 kHz (assuming no ageing on the capacitor has occurred to affect the frequency).

    Dave

  6. #46

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    As unconventional as it looks, that capacitor looks as though it was always there so it's useful to know that the resulting frequency comes to under 1Mhz. Strange thing to do though, when all indications are that the Introkit kit included a crystal.

    Maybe that changed at some point (cost saving measure?)

  7. #47
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    I agree.

    Just had a PM conversation with Gabriel. They will be back soon...

    Dave

  8. #48

    Default The two INTROKITS mentioned in PE review in March 1977

    Interesting thread - the fact there are two European Introkit designs is mentioned the March 1977 review in Practical Electronics...

    https://www.americanradiohistory.com...cs-1977-03.pdf

    The first with the Crystal in the top left is the older model (pictured in the header to the review) and also the built one at TNMOC in the photos above, the one with the Crystal at the bottom right of the printed area is the unbuilt one at the TNMOC and the one the Keyboard KIT references. Note that the reference to two different kits in the KB manual is to the shorter one from the (likely) US and the European INTROKIT - not to the two European versions. This other (likely US) design is pictured on Page 15 and 16 of the Keyboard kit manual and the one mentioned /shown in the main Introkit manual.

  9. #49

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    Sorry for the delay in responding, but I did not have enough time in the past weeks.

    Quote Originally Posted by SiriusHardware View Post
    Can you explain or show what you are powering the system with?
    I powered with a Mean Well RQ-50B (datasheet: https://www.meanwell.com/productPdf.aspx?i=375#1).
    (The 5V output is adjustable - CH1: 4.75 ~ 5.5V -.)

    Quote Originally Posted by SiriusHardware View Post
    An oscilloscope is a great tool...
    I ordered a cheap one, which daver2 mentioned (DSO150).

    Quote Originally Posted by SiriusHardware View Post
    You mentioned you have a multimeter, does that have a frequency measurement (Hz) feature on it?
    There is no such function in my multimeter.

  10. #50

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    Quote Originally Posted by daver2 View Post
    You can test the ROM out of the board on a piece of breadboard with 8 LED's, 8 current limiting resistors...
    Thanks for the idea. Before I do this I wait for the oscilloscope to arrive.

    Quote Originally Posted by daver2 View Post
    If you haven't already done it, check the wire wrapping for bent and/or shorted spills and the wiring for broken wires before anything else.
    I check the wire wrapping and I don't find any problem, but I'll look it over again.

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