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Thread: Science of Cambridge (Sinclair) MK14

  1. #71
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    I'll check mine out with a multimeter and post the results at the weekend.

    Dave

  2. #72

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    If the machine is in working order then a multimeter on an amps range can be used as a handy testing link with convenient built-in probes - connecting row '0' to column '0' should make a '0' appear on the display, connecting row '0' to column '1' should produce a '1', and so on.

  3. #73

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    Quote Originally Posted by Timbucus View Post
    I am also lurking here (as the person SH mentions) as I have recently built a JM replica.
    Good to find you here as well Tim, although I see you are subject to New User moderation / delay here as well, which explains why I did not see your post pop up until now. I'll leave it to you to explain the steps that were necessary to get the uploader working properly on your JMP replica PCB. I'm not sure there is much interest in the uploader project here with this being a mainly USA-centric forum (and the MK14 a niche British item) but, having posted about it initially, the least I can do is try to keep the info current and up to date with any necessary mods and updates.

    All this VHDL stuff goes completely over my head, I'm still stuck in the late 1970s where microprocessors were real microprocessors. I've never even tried to do anything with programmable logic, so I'm way behind now in that respect. An MK14 on a chip would be something wonderful to see, especially if it incorporated the VDU and enough RAM, perhaps mapped at 0200-07FF, to support it.

  4. #74
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    Yes, I did get my MK14 VHDL 'working'. I will qualify the 'working' bit though - it seemed somewhat temperamental...

    I suspect I have an unintended clock race hazard somewhere - but I couldn't find it at the time. I will be quite happy to upload my VHDL to my google drive if you give me a bit of time. I am somewhat busy at work at the moment and I will be away for a week on business.

    Perhaps I will have another look at the VHDL code after I have copied it.

    Dave

  5. #75

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    Quote Originally Posted by daver2 View Post
    Yes, I did get my MK14 VHDL 'working'. I will qualify the 'working' bit though - it seemed somewhat temperamental...

    I suspect I have an unintended clock race hazard somewhere - but I couldn't find it at the time. I will be quite happy to upload my VHDL to my google drive if you give me a bit of time. I am somewhat busy at work at the moment and I will be away for a week on business.

    Perhaps I will have another look at the VHDL code after I have copied it.

    Dave
    Dave, that would be wonderful, no hurry as I have a lot of projects under way - not that I have done much myself Mr SiriusHardware, just been following the work on the Next core so picked up a bit chatting to to Victor and Allen. This seemed like a project (as long as somebody had done the back breaking work) that would be challenging enough to allow me to truly learn the technology with a valuable final output - not sure how many of the 3000 next users would be interested in an MK14 but, well some would.

    As SH alludes to on my board I had to change the Reset values in the send14 script (the two time.sleep statements on the reset case) to hold low for 0.1 and recover for 0.2. On a scope the default values do not actually fully zero the Reset on my brand new 25uF capacitor so the reset is unreliable. The 0.2 came from measuring the time to full return to 5v - that was erring on the side of caution as of course it would be usable after about 2.5v - in the end the reset is only done once at the start so does not affect the upload time much.

    Tim

  6. #76

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    Since Tim brought this up I have taken a closer look at the sole electrolytic capacitor on my 40+ year old MK14 - which happens to be the reset capacitor. There is a suspicious looking malachite green tinge around the first 2mm or so of the +ve lead of the capacitor next to the body, suggesting that something may have vented or leaked, and bringing into question the likely health and actual value of the capacitor.

    I don't like taking any original parts off genuinely antique equipment but I recently nearly had another microprocessor PCB damaged by a weeping PCB mounted nicad battery which had turned many of the component leads in the immediate area the same malachite green, so better safe than sorry: I've ordered a replacement. I will keep the original part and may consider 'repairing' it by fitting a smaller, more modern 22uF axial capacitor inside it in due course.

    What I am expecting to find is that replacing the capacitor with a new 22uF will lengthen the reset timing substantially, and will stop the 'Reset' feature of the uploader working until I change the reset hold / release to the values which Tim has arrived at: I think Tim's initial problems were caused by my not realising that the reset capacitor on the machine I used for testing / tuning / finalising the timing values was in such bad condition, so I'm grateful for all the patient investigation work that he has done.

  7. #77
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    I have uploaded my prototype VHD files for the MK14 to the following link:

    https://drive.google.com/drive/folde...aI?usp=sharing

    Please accept the fact that this lot is poorly commented (not to my usual standard at any rate)!

    The logic was designed to run on a Xilinx Spartan 3E starter board. This card has an RS232 connector, a VGA screen and a rotary encoder.

    I wired the MK14 serial in and out to the RX and TX of the RS232 converter.

    I used the VGA screen as the seven segment displays plus the keyboard plus a diagnostic display and used the rotary encoder to select which key I wanted to operate. Pressing the rotary encoder selected they desired key that was highlighted.

    I loaded some 'test programs' into the RAM image...

    You will also see I had a go at the VDU.

    Any questions please ask.

    Dave

  8. #78

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    Thanks very much Dave - I have downloaded a copy and will take a look through, understand it is WIP and appreciate you sharing, a quick glance seem to indicate plenty of comments (maybe I just put less...) - I hope to have some time over Easter to take a look at this so the timing is great.

    Regards

    Tim

  9. #79

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    A brief update: The reset capacitor on my MK14 turned out to be healthy despite appearances, but I replaced it anyway and tried the uploader again without changing my original 'fast' timing values. It still worked.

    As part of the process of narrowing this problem down, Tim sent me the SGS-Thompson 74LS365 he had originally fitted as a pin-compatible substitute for the 80L95 (as originally supplied by SOC and fitted in my machine). When I fitted this chip in my MK14, the uploader stopped working and did not work even when I increased the reset hold and release times to Tim's suggested new values. Instead, I saw the MK14 reset more slowly than usual and then it ignored all the key presses following, probably because they were not being held on for long enough.

    For 'Normal' MK14 operation, manual key entry and so on, Tim's SGS 74LS365 works fine, but the 74LS365 chip Tim now has fitted is obviously allowing the MK14 to read much shorter key presses than this SGS chip does because it lets the uploader fire keypresses into it at a much higher rate. It might be interesting to see what would happen if I fitted an original 74365, assuming one could be found.

  10. #80

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    Dave,

    Thanks for sharing that code - I managed to get it running on my Waveshare Spartan3 board using a rotary encoder from my Arduino kit and a small keypad / VGA adapter. The code needed modifying to use the 3 RGB level VGA and obviously the totally different pinouts. I also stitched in an external Keyboard connection so that I could use Sirius Hardware's PI-Programmer to to type in more software and act as a real keyboard.

    IMG_1378.jpg

    I cannot get MOONLAND to run either the built in one or one typed in from the PI-Programmer which works fine elsewhere - the much larger SEGTRIS loads and plays fine if a little fast - as you say in the code the timing needs a bit of work...

    Can you confirm if MOONLAND ran OK on yours or was that one of the funnies you had? If it does not work on yours either then I will look perhaps for an SC/MP or display emulation error.

    The code contains no copyright statement and although you have shared it above on a public forum I would appreciate if you could clarify how you see that as I would love to get it running on the Spectrum Next (a Spartan 6) and if you were OK, allow the voluntary dev team (who I will need help from to add the outer VHDL wrapper) to eventually include it with the distribution - most of which is GPL or similar open source licences - if code has none they add a generic project one with the named authors with the usual liability exclusions...

    My idea was to provide a decode for the Spectrum Keyboard on it and full screen the VDU / segment display by pixel doubling! There is already a QL ( 68008 ) core on its way and it would make the machine a nice self contained - everything from Sinclair - so that others could explore the MK14 if they wish.

    Tim

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