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Thread: Replica Science of Cambridge MK14 available for pre-order.

  1. #21
    Join Date
    Dec 2010
    Location
    Stoke-on-trent. U.K.
    Posts
    178

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    Just building my replica now.
    I have two questions:
    C1 is stated as "27p for 33p".
    Does that mean 22pf OR 33pf or something else?
    And the proms I got included in my kit (my burner doesn't handle proms) one has a green sticker and one has a blue.I presume these are not interchangeable so anyone have an idea which one is which?

  2. #22

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    27 or 33 pF will work.

    This is how I placed the ROMS:

    2018-05-17 19.40.06.jpg

  3. #23

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    This was actually Science Of Cambridge's own method of identifying / differentiating between the two proms, one of which holds all the lower 4 bits of the OS and the other of which holds all the upper 4 bits of the OS. Side by side they provide 512 bytes of 8-bit wide PROM memory.

    Even the colours of the stick-on dots (green and blue) are authentic.

  4. #24
    Join Date
    Dec 2010
    Location
    Stoke-on-trent. U.K.
    Posts
    178

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    Thanks for the info.Read through the MK14 manual and coudn't see any reference to how the proms went apart from the list of parts that said one had a "whitespot".

  5. #25

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    I should have clarified: The green spot / blue spot convention applies to the 'new' or 'updated' version of the OS, the presence of which is identifiable by the fact that it comes up with a 0000 00 prompt after reset instead of the original ---- -- prompt as described in the manual.

    The info regarding fitting of the blue spot / green spot PROMs came with those in a leaflet supplied with the revised OS when it was bought as an upgrade.

    The same leaflet also explains the differences in the way the new OS operates - with the new OS it takes far fewer keystrokes to enter data and the new OS also contains support routines for a jump offset calculator, the optional single step hardware and most crucially, the optional cassette tape interface. I don't know if this info can be found on mk14man's site, if not I will scan it and upload it.

  6. #26

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    Note: with the new version of the ROM's you need to connect pin 26 of the expansion connector to GND (e.g. pin 6) otherwise you can not start any program with the GO button.. (took me a while to find that one out, it is mentioned in the second version of the MK14 manual)

  7. #27

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    Yes, that will be Sense-A, Sense-A is used by the revised monitor along with a small amount of additional hardware and a switch to provide the optional 'Single Step' function.

    If the additional hardware and switch are NOT fitted when the revised OS is fitted, Sense-A must be tied low with an actual wire link or low value resistor otherwise the OS will not run normally.

  8. #28
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    1,918

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    I have been trying to find the SCIOS upgrade leaflet for ages on the internet - but with no luck. If you have a 'real' copy it would be very useful if you could upload it to somewhere. Cheers!

    You can see the green and blue stickers on the ROMs here (just): http://www.8bity.cz/wp-content/uploa...no_working.jpg.

    Martin has some better images of the ROM placement on his website. I just can't easily find them at the moment. I will have a better look later.

    EDIT: A better link http://www.8bity.cz/2018/tips-for-bu...-mk14-replica/...

    I am also constructing a set of cards as well (MK14, VDU and cassette). I have a few items to still find yet though. Do you want me to post any links to specific items if I have already tracked them down?

    Dave
    Last edited by daver2; May 21st, 2018 at 03:00 AM. Reason: Found a better photograph of the 'blue and green stickered' PROMS

  9. #29

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    I found this manual for version 2

    http://www.8bity.cz/files/MK14/mk14ManualV2_OCR.pdf

    Created my own tape interface on a piece of double sided 'veroboard', alas I did not have a 4001 at hand so I used a 4093 instead, just need to connect the one input of the oscillator gate to another point (one inverter less in the path):

    2018-05-18 22.55.26.jpg

    Need to add the extra 27k resistor with D1 (no type specified in the manual?)
    Last edited by gertk; May 21st, 2018 at 12:49 AM.

  10. #30

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    Gert, that's a tremendous find. I had no idea Science Of Cambridge had ever even produced that V2 manual. Thanks for flagging it up.

    For completeness, I will in any case scan and upload the 'manual' which came with the revised OS when it was bought as an upgrade by 'Early Adopters' of the MK14, as it's one of the few original MK14 related documents which seems to be 'Missing From The Internet'.

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