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Old 12th Nov 2021, 11:47 pm   #801
SiriusHardware
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Default Re: MK14 schematic revisions

I suppose you could always have a 40 pin socket-to-pin passthrough to still have an 8154 plugged in and accommodate the EPROM (as PROM replacement) on a bit of PCB extending out to the rear.
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Old 12th Nov 2021, 11:58 pm   #802
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I suppose you could always have a 40 pin socket-to-pin passthrough to still have an 8154 plugged in and accommodate the EPROM (as PROM replacement) on a bit of PCB extending out to the rear.
That's why I made my PROM replacement just plug into the PROM socket with flying leads for D0..D3, its a lot neater than having it plugged into the 8154 socket and doesn't prevent you fitting the 8154.
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Old 13th Nov 2021, 12:07 am   #803
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Default Re: MK14 schematic revisions

If you made the board with two offset 'wings' at the lower left and upper right corners you could even eliminate the flying leads (board would plug straight into both PROM sockets via descending pins long enough for the board to float above an installed 8154).

However, a board like that would be mainboard specific, it would only fit whatever kind of main board you made it for, issue VI or something else, depending on the distance between, and relative positions of, the PROM sockets, whereas your original idea handles that problem.
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Old 13th Nov 2021, 12:43 pm   #804
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Default Re: MK14 schematic revisions

Well Martin's 8-bit blog on the MK14 stuff did provide a PCB that piggybacked on the SC/MP chip and replaced the Prom and Ram chips, but left the INS8154.

It used a GAL16V8 to handle the address selections, which is clever but also makes changing it more of a challenge.
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Old 13th Nov 2021, 12:50 pm   #805
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Default Re: MK14 schematic revisions

I try to shy away from things which might be difficult for other hobbyists to programme, like GALs, although I'm sure someone will promptly tell me that there is an Arduino project made for just that purpose.

Slothie's issue VI board, with all the bus and control lines uniquely brought out on the rear edge, allows any such expansion to be plugged into the rear edge connector in trademark Sinclair fashion. If I was targeting the issue VI only I would probably do it that way.
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Old 13th Nov 2021, 3:39 pm   #806
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As you suggest, there are many, many DIY GAL programmers out there as the programming algorithms for the various manufacturers have long been reverse engineered and made public, and some types can be programmed with the cheap TL866 programmers that are everywhere. My only hesitation is that they are essentially 1970s tech and designing them into new designs is just asking for supply problems, those available are "old stock", Atmel/Microchip are currently still making them as far as I am aware but the TL866 has varying success depending on who on the internet you talk to - its possible that the latest versions of the hardware and software might work because some comments on EEVBLOG forum imply that they do.
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Old 13th Nov 2021, 5:05 pm   #807
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Default Re: MK14 schematic revisions

A fast modern eprom or EEPROM would probably be the most accessable / reproduceable custom address decoder but then you'd have two wide bodied EPROMs on the board, one the address decoder and one the memory device so it wouldn't be especially small.

It's probably still more economical to use one or two TTL devices with hardware links to set two or three different decoder configurations.

As a matter of interest the old programmer which I use to program BPROMs with also supports a wide range of GALs, so if anyone does need a one-off done that shouldn't be a problem provided you have the programming file as well - I wouldn't even know how to start defining the programming of a GAL myself.
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Old 18th Nov 2021, 3:23 am   #808
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Default Re: MK14 schematic revisions

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Slothie has suggested that modern 7-segment LEDs are a lot brighter for less current than their equivalents from 30 years ago, so maybe you could insert series resistors and not lose too much light output.
ChrisOddy has recently found that the FYQ-3641AUHR-21 4-digit 0.36" / 9.20mm high displays (that I'd linked to a datasheet of earlier this year in this thread about ones to fit Trevor Hamblett (0.36") PCB's) give very good brightness at fairly low currents
- On an Acorn System-1, where they choose to directly-source the high-side current from the 8154 (rather than use the 7408 AND-gates as high-side buffer/drivers that the MK14 had, as they'd got away with it on the original 8/9digit bubble display). But some recent (modern) single digit ones he'd initially tried, were much lower brightness (I'm sure he'll reply with the type number of those not recommended to use ones).

It seems he managed to get some of these quite cheap from some online marketplaces, although I've only found rather high prices from these, from a quick look.

BTW, if anyone in the UK is after 8154's at considerably less than Littlediodes price, then Chris has some available on his website etc. - Which can save a lot of hassle trying to order from the Australian Rockby company (one of the few places still stocking these), and having to deal with import duties / working out how to pay them (seem they don't take cards or Paypal etc!)
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Old 18th Nov 2021, 3:54 am   #809
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Because the available information regarding programming of the Tesla devices was so poor and not in a convenient language (for us), anyone who has come up with a working unit since then will no doubt have perused all available information on the subject including your project thread - this site is never far from the top of the list of google hits for a search on any subject which lies within its remit.

I can understand Owen and Chris choosing to use the timing / algorithm of a commercially made Elnec programmer as their main benchmark because that would have been one of the few commercial programmers made with the approval of the chip manufacturer and based on exact information supplied by them.
Yes, While Chris was trying to modify the Acorn System PROM-Programmer to support the Tesla PROM's (As all stocks of the NS ones now seem to have been finally exhausted), he was having difficulty interpreting the rather vague / contradictory datasheets (TI didn't actually make a correct-size equivalent to these ones).
So as the ELNEC-designed Dataman-Pro we had access-to, did work OK, then we made some measurements on it, to establish what timings / voltages were being used.
We discovered that it was a bit more intelligent than EPROM-programming, in that it only tries to program (blow) a fuse, if the particular bit hasn't already been fused, rather than just blindly-attempt to (re)program each location.
So I had to do some improvisation with resistors and diodes to bias a databit to an unfused state, but still be able to measure programming attempts to it on a 'scope.

Although it seems ELNEC have good contacts with many programmable IC manufacturers to obtain info that isn't always included in the datasheets / are based in a similar area of the World to where the Tesla PROM manufacturer was. So probably had best-chance of supporting these devices.

However we did discover that it only used one fixed-length programming pulse once on each location. And if any failure was encountered it just aborted rather than retried that location. (It seems it did the same for NS ones, as the first one I tried to program for Chris, took quite a few minutes of repeating the whole cycle, before all locations programmed OK with an old blank device he'd bought)
Whereas the Texas provided algorithm was a bit more intelligent of using many short pulses(but total length below typical required pulse duration to fuse it), before switching to some longer pulse-width ones.
You do also need to allow cool-down periods after programming each bit, but it seems several programmers didn't really stick to the spec. for this (maybe trying to make programming faster)

So whilst the ELNEC-designed Dataman-Pro came in handy for looking at levels and some timings, it probably hadn't got the best overall algorithm for doing these devices (Although their EPROM & FLASH etc. programming ones do generally seem very good) and it seems they may have just opted for simplicity rather than a more complex algorithm.
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Old 9th Feb 2022, 6:15 pm   #810
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Default Re: MK14 schematic revisions

I have a 'watch' set for MK14 related items and I still see bare issue VI PCBs come up every now and again, I tend to wonder what happens to them. For all the time this thread has been going for now you would think that some of their owners would end up dropping by here - and maybe they do, but in read only mode.

I was trying to think how many working issue VIs we know of and I know that Slothie (of course) has one, I have one, Tim has one, Mark has one... Buzby has the only named one in existence (Vicky). Have I missed any? I vaguely remember a built one being sold online, but only that single example.

Philoupat over in France has one of my black issue VI PCBs but I don't know if he ever built it up.
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Old 9th Feb 2022, 6:46 pm   #811
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Default Re: MK14 schematic revisions

Well I have one of the Version VI boards - not yet built - got all the bits but I need to find time and the energy to put it together.

My working one in from Martin which I think is closer to the original MK14 board.

Stay safe
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Old 9th Feb 2022, 8:18 pm   #812
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The Czech 'Martin' issue V replica is undoubtedly the closest to the real thing in terms of looks and aesthetic and the placing of the components, especially with the type of PCB used and the remanufactured keypad which really puts the finishing touch to it.

For actual usability I think the issue VI literally has the 'edge', as in all of the bus signals taken to the rear edge connector. No other original or replica PCB has that, as far as I know.
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Old 10th Feb 2022, 12:43 am   #813
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I was trying to think how many working issue VIs we know of and I know that Slothie (of course) has one, I have one, Tim has one, Mark has one... Buzby has the only named one in existence (Vicky). Have I missed any? I vaguely remember a built one being sold online, but only that single example..
There was that guy who was selling an overlay and 3D printed frame for the keyboard, I messaged him and suggested he pop by here if he needed help but I don't think he's come to light.
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Old 10th Feb 2022, 1:00 am   #814
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Default Re: MK14 schematic revisions

Through the PICLV2 project I've made contact with another original MK14 owner, I'm hoping Alan will join in as his MK14 is faulty and I told him this is where the experts hang out
.
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Old 11th Feb 2022, 12:55 pm   #815
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Default Re: MK14 schematic revisions

That's an interesting thought, I don't think we have ever had an 'MK14 repair' thread - Buzby kept us updated from time to time on progress on his 'Micky' but he didn't actually need any help to get it going.

They occasionally come up under the 'Other' category over on the USA-centric Vintage Computer Forums (VCFED), but not often. I notice they've added a 'Sinclair and Amstrad' subcategory over there and an MK14 thread has been lumped into it to help to get it started.
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Old 24th May 2022, 8:19 pm   #816
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Default Re: MK14 schematic revisions

Well finally got all the bits together, and found the time to build my version VI of the MK14 - thanks to all those that helped me. I got one of those 3D printed overlays and they look quite good.

Still need to add a few of the 100n capacitors and check that it all works but it is looking good.

David
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Old 24th May 2022, 9:19 pm   #817
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Nice I like the display. good for eyes my age
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Old 25th May 2022, 8:21 am   #818
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Just needs an 8154?

Someone mentioned a while ago that Chris Oddy who occasionally appears here (and now offers an alternative repro MK14 PCB) might have some for a reasonable price.

As I've said before the improvements on the issue VI, especially the tracking of all of the system signals to the rear edge connector, make it the 'user's choice' because it is so much easier to play around with. My original issue II MK14 is now essentially mothballed, mainly to preserve it, although it will get a run out every now and then.
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Old 25th May 2022, 10:00 am   #819
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I've been looking at the 6532 RIOT as a replacement for the 8154, but like the 6520 and 6522 it needs the 6502's phi-2 signal that times the I/O cycles and clocks the timer. I don't doubt that the i/o timing can be solved, but doing so from the SC/MP's signals so that the phi-2 is a at the same time constant enough frequency to make the timers useful would be problematic.
From time to time the 6532 becomes available fairly cheaply which is why I was considering it. Perhaps if one ignored the timer function it could still be useful, as it has 2 8 bit i/o ports and 128 bytes of memory.
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Old 25th May 2022, 10:23 am   #820
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Actually an independent timer 'feature' built into an add-on I/O IC would be a really useful feature, for example my interest in getting some kind of MIDI interface working with the MK14 has not gone away but I would automatically include some kind of offboard digital 'metronome' on any such interface - something that the uP could poll - so that the 'playback' speed did not have to depend on exquisitely crafted software timing loops - the sort of thing Karen thrived on, but which I just don't have the patience for. OK, the skills for.
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