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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 11th Apr 2019, 3:02 pm   #161
SiriusHardware
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Default Re: MK14 schematic revisions

The online emulator is unusable, slow and unresponsive on its default settings - you have to ramp the cycles per second value up to the maximum and I find I have to change the display type as well to get it to run at a reasonable speed - and also it only seems to respond on the keypad meant for tablet users as well, for me - sorry I can't be more specific but it has been a while since I used it.
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Old 14th Apr 2019, 1:17 pm   #162
Timbucus
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Default Re: MK14 schematic revisions

Again keeping more general MK14 stuff in this thread - following SH's suggestion of looking through Practical Electronics I started with the original review (which is reproduced in text on the net) in the May 1979 issue. Off Topic I was shocked when the cover featured the IC insertion tool I had used to help build my replica - surprised I still had it and the elastic was still working! I only lamented it was too small for the 18pin PROMS and RAM!

https://www.americanradiohistory.com...9-05-S-OCR.pdf

I had read the text but, with the photo's I notice that the VDU board he mentions is not the SoC one but, the one built and described in PE itself over three issues from Oct 78 to Dec 78. - just change the number in the url to 11 and 12 to get to the other two parts...

https://www.americanradiohistory.com...cs-1978-10.pdf

This solves the problem of slowing the MK14 and and using its memory with its own onboard 1K. The review also describes the changes needed on Rev I-IV boards to remove the PROM shadow - which is where they map the Video RAM.

I have the parts on the way to build the SoC one but, that looks like an interesting project to reproduce the PCB - not sure if any of the chips are still available...

again as an aside I still have some 7400 chips with the free stickers from the Oct 1978 cover on them...

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Old 14th Apr 2019, 6:08 pm   #163
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Default Re: MK14 schematic revisions

Yes, the PE VDU was a much more sensible beast than SOC's own effort. I've never seen one.

For the SOC VDU, be aware that one of the ICs on that - the character generator IC - is quite a specialised IC and may be hard to find now. It was actually an option which did not automatically come with the VDU kit, you had to pay extra for it. It still sort of works without it, but only in dot-matrix (graphics / pixel) mode. If you want to use it in its text / character output mode you'll need the character generator IC.

If Slothie manages to track the VDU connections to the rear edge -and- removes the images from 0200-07FF (a big ask) then there is the possibility to place a 'ram pack' in between the MK14 and the original SOC VDU, or just by itself to give the machine a respectable extra 1.5K of RAM.

Unfortunately the butchery required to my issue II board to get rid of the images in that range would not only be too great now, it was too much for me to consider then and I never did it.

Even when hooking the VDU into the MK14 in the manner intended there were a few required changed such as track cuts and a change to a 4Mhz crystal, so it was quite a destructive process. Mine still bears the scars, even though I have modified it back to near original state, except for the keypad of course.

..I remember those stick-on IC diagrams, a good idea I thought but of course you always ran out of the common ones pretty quickly.
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Old 15th Apr 2019, 12:42 am   #164
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Default Re: MK14 schematic revisions

... Just caught up with your latest MK14 article finds.

That one with the image of the super-early-version MK14 is great, I don't think I have ever seen that one before. I have never actually heard of, or seen, an actual issue I MK14. All the ones I've ever seen are issue II or later.

Yes, an acknowledged weakness of the cassette audio signalling format is that it starts sending significant information immediately - this was addressed in later Sinclair machines by sending a long preamble of steady tone to let the recorder AGC settle before starting to send significant data.

I've never heard of the interesting HF injection method to pre-adjust the AGC action before but another forum member here (Gert?) had the brilliant idea of inverting the data before sending it to the cassette interface so that the signalling is done, not by silence broken by 4ms or 16ms bursts of tone, but by interrupting the otherwise continuous audio tone for either 4ms or 16ms. That would provide a lead-in tone for the recorder to adjust its gain on before any significant information begins to be sent.

I was actually wondering if we could (or should) collect all the links to known sources for MK14 software and hardware projects into a thread of its own, which might also incorporate some discussion about actually programming the machine - there's a lot of interest in recreating the hardware but people rarely write anything new to run on them (I am as guilty as anyone else).

I've been contemplating the idea of setting up a small model railway circuit and trying to do some basic PWM speed control and automatically starting from / stopping at a station - I have some (N gauge) sectional track and a few models to put on it, but no electrically controlled points, so it would have to be quite basic. I think this is the sort of experimental Arduino-like hobby control application the MK14 was originally aimed at.

Another, less physically complex and more self contained project might be to connect an alphanumeric LCD display to one or both of the 8154's I/O ports and recreate the 'Message' program with the message scrolling on the LCD display with no crippling literary limitations imposed by there being no Letters 'K', 'M','P','Q', 'V', 'W', 'X', 'Y', and 'Z'.
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Old 15th Apr 2019, 8:25 pm   #165
Timbucus
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Default Re: MK14 schematic revisions

As regards the SoC VDU - Martin has a substitute part a DM86S64CAB which he has managed to get - not sure how much stock he has but, its a useful source with the PCB.

I think the idea of collecting articles and links in a thread is great - this one is sort of doing it. I have been pulling together a set of personal notes on topics which may help form an FAQ. A wiki would be ideal somewhere perhaps...

That's funny I describe the MK14 to people as the Arduino of 1978 so a model train controller seems ideal...

I am also guilty of not doing any coding (yet) - as a Z80 programmer I am having a bit of a shock reading what is available on the SC/MP II first!

The Alphanumeric LCD display ties in very well with my first intended project which is to port my adaptation (which is 256 Z80 bytes) of an i2c and RTC driver from the Next! That is what I am working up to... now I have actual hardware and a cross assembler.

Other magazines of the time may have something of interest if not directly MK14 then SC/MP (E.g. Elektor who had the designs for a machine based on one if I remember correctly). One I quite fancy having a go at is 2 dimensional version of Conway's game of life described in Issue 12 of the 1978 Byte:

https://archive.org/details/byte-mag...78-12/page/n69

The magazines suck up research time ( I have to stop )...

I have also just been naughty and bought a copy of Issue 2 of Personal Computer World (May 1978) as they are not archived online anywhere. It has a review of the MK14 in it (I noticed as the listing included the contents page) which I will obviously scan - interestingly it is written by Nick Toop. I think it may be the same person who in PE of April 1979 provides an MK14 diagnostic program written in NIBL BASIC - he is described as working for SoC then and is credited as the designer of the VDU board... He has a further article in the Dec 1979 PE issue with an Output Flag multiplexer and falling man animation for the VDU.

The bit that really interested me in the above is the mention of NIBL at SoC I wonder if they had somehow put the ROMS (2 off 2316A for 46.90 from Greenbank Electronics) into the MK14 memory map or were using a more powerful SC/MP system. That started me thinking that if the top four address bits were latched and some mods to the onboard address decoding were done it could appear as another 4K Page... only problem would be the SCIOS reliance on the RAM at FFF appearing to wrap below 000. A future project...
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Old 15th Apr 2019, 10:58 pm   #166
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Default Re: MK14 schematic revisions

I love Z80, when I was playing about with my Maplin Z80 system a while ago I was struck by how luxurious the instruction set seemed. I remember a lot of the opcodes even to this day. Of course, this marks me out as coming from the Sinclair tribe - I still have my original ZX81 and 48K Spectrum, along with a couple of other Sinclair machines which were not originally owned by me.

The main things I wish the SC/MP had are CALL and RET instructions and a proper stack pointer to support those.

Having a cross assembler for SC/MP is the final link in the chain - once you have that and combine it with some way of getting your assembled code into the MK14, the MK14 is almost as much fun to play with as an Arduino, PIC or AVR, although of course all of the latter have extra goodies like built-in UART, I2C, SPI, Timers, analogue inputs, PWM outputs...
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Old Today, 9:29 am   #167
Slothie
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Default Re: MK14 schematic revisions

I've been looking at my latest PCB design and to correctly decode the ROM to allow extra memory in the lower 2k is going to require an extra logic IC and the requisite rework to squeeze it in somewhere and still make it look authentic. Still, perhaps that will give me something to think about! I've attached the schematic up here and perhaps you could tell me if the connections on the bottom row (P4) look good to connect the VDU. Note that due to the orientation of the connector, the power (+5) is on the right under the top power connections, and the address lines will be on the right hand side (IE nearest the vertical resistors).

PS I'm back in action after my operation though it will be a month or so before I discover how successful its been - so till then I'm a one-eyed sloth!!
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