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Old 25th Jun 2019, 10:53 pm   #201
Timbucus
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Default Re: MK14 schematic revisions

I will pass on the thanks - I gave him the link to here so he may appear at sometime hopefully...

Quote:
Originally Posted by Slothie View Post
Since a queue is forming I'd better check that its going to work carefully!
Indeed - although the review for the MK14 did rather unfairly say the most fun you would have with it was building the kit... so perhaps by extension debugging the kit should be even more fun?

On a more serious note, I hope to have some time (when I am not tired) this coming Sunday to look over the design in more detail just as a double check for you. As yes it starts to gets scary when others want to use your stuff - so then I will only have myself to blame for any mods we need to get them running. Let us know if you need some cash to chip in for the prototype run.

Reading through CAA in Issue 5 the review of the VDU suggests hooking up B13 to Flag 1 , B14 to Flag 2 and B16 to flag 0 - so we are breaking canon! Using the IO chip is better though I think.

It also hints at how the memory board was configured to allow sockets for 2111, 2x2114 and some 74S571 PROM - not sure if that is the proposed SoC one or their own. I may find out in the next instalment - exciting, not sure I could have waited a month for a chain letter to arrive or not! Right back to archive.org.
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Old 25th Jun 2019, 11:27 pm   #202
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by Timbucus View Post

in Issue 5 the review of the VDU suggests hooking up B13 to Flag 1 , B14 to Flag 2 and B16 to flag 0 - so we are breaking canon! Using the IO chip is better though I think.
The original instructions for the VDU say to do that (use the Flag outputs), otherwise it would have excluded people who did not have a RAM I/O fitted - bearing in mind that the RAM I/O was an option, not standard.

People generally did not use a 'hard' one to one connection between the VDU and the MK14, so they were able to choose which flags or I/O lines to connect for these purposes.

One minor problem I forsee (I have not thought it through, but...) you will want the VDU to be disabled on MK14 reset, because when it is enabled it constantly halts the CPU and drags the overall system speed right down, meaning that the cassette interface or any scheme which uses it indirectly (ie, Serial download from PC as per Karen O's idea) and for that matter the Pi uploader will not work, unless of course you slow the latter down to the speed of mud.

The I/O device I/O ports start off in high impedance input mode so a pull up or pull down resistor (can't remember which) will be needed on the 'display blank' connection to hold the VDU off until such time as the user puts that I/O port pin into output mode and intentionally turns the VDU on.
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Old 26th Jun 2019, 9:47 pm   #203
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Default Re: MK14 schematic revisions

One final idea for Slothie before he sends his design off to be made into PCBs - How about putting a copper trace 'Issue VI' in the appropriate place on the track side of the PCB?

With the buses tracked to the rear edge and support for alternative RAM types, it really will be the most advanced 'legacy' MK14 PCB, original or replica, ever made*. I think it deserves that finishing touch.

*MK14man's noughties version was a contemporary redesign, rather than a 'what-might-have been'.
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Old 26th Jun 2019, 10:57 pm   #204
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Default Re: MK14 schematic revisions

Yes I think that would be lovely - the MK14 ISS V is above the extra keyboard fingers (which appear on the bottom as well as the top) of Martin's board so his is of course a perfect replica except for that which is an extra - so he is probably 5.1!
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Old 26th Jun 2019, 11:34 pm   #205
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Default Re: MK14 schematic revisions

Thats an Idea!
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Old 29th Jun 2019, 5:46 pm   #206
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Default Re: MK14 schematic revisions

Actually I had a thought that what might have been next for SoC would have been a way to disable any activity on the board in PROM, MEMORY or IO so that extra 'pages' could be added with a latching circuit for D0-D3 which holds the high Address lines A12-A15 during NADS - i.e. the BoardEnable would only trigger on four zeros for Page 0. This would have been needed for the NIBL BASIC expansion card or larger PROMS etc. I must study the circuit and see if there is a simple way that could be added - probably by routing the RD/WR enables to an off board option with a pair of links for a bare board. Break the links and add the extra circuit for pages to work is on the expansion card.
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Old 29th Jun 2019, 6:39 pm   #207
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Default Re: MK14 schematic revisions

I tried something like that about 35 years ago. A hand-wired (on Veroboard) SC/MP system with the low 4 data lines latched on NADS to give the full 16 bit address bus. And I tried running the MK14 monitor ROM on it.

I discovered (the hard way!) that said monitor does not put everything in page 0. I seem to remember it addressed the keyboard and display in a higher page -- page 9?
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Old 29th Jun 2019, 6:52 pm   #208
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Default Re: MK14 schematic revisions

Ah interesting - I had read about the reliance on the wrap around at the end of the page for the variables at FF9-FFF which I thought might initially prevent the use. But after further study (especially the Elektor articles on adapting NIBL for page 1 onwards) I suppose that the above must be a bug in the monitor, as the pointers do not increment beyond Bit 11 supposedly so only XPAH and XPPC can change the page, something using one of those instructions must set those bits incorrectly.
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Old 30th Jun 2019, 1:57 pm   #209
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Default Re: MK14 schematic revisions

As there have been some questions about the connectors on the PCB, and I admit that the schematic doesn't really help, here are some pictures of the connectors as rendered in the 3d view. I have marked what each connection is on the silkscreen, since I personally will find this helpful, and I am sure that others will too.
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Old 30th Jun 2019, 7:34 pm   #210
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Default Re: MK14 schematic revisions

Certainly will, rather nicer than having to scrabble for my threadbare piece of paper which describes the upper rear edge connector, and of course especially helpful to have the rear lower side connections labelled since your PCB is unique in having those already routed so there is no existing documentation which describes those connections.

I don't know whether SOC would have ever have gone so far as to implement memory paging as suggested by Tim / tried by Tony, but they might and ought to have got to the point where the bus connections were all available at the edge connector (they did, after all, do this on the ZX80 onwards from the very start). They should have done it on the MK14 on the first issue which had contact fingers for the lower side of the rear edge connector, whichever issue that was.

If they'd done that (and with the unwanted PROM images already removed from issue V onwards) they could have introduced a 'RAM pack' PCB which plugged into the rear edge connector in the best tradition of Sinclair machines going forwards from that point, perhaps with an ongoing connector on its own rear edge, appropriately pinned out for the VDU via a DIN connector of the same type which the VDU was obviously laid out for. (Your third or fourth next project, perhaps...)

Incidentally the same forum member who confirmed that the issue V did have those unwanted PROM images removed 'out of the box' also told me that there are still multiple images of the RAM I/O and display in the issue V memory map, so he then further modified his issue V machine to remove those images as well. I invited him to post details of the mods (in the area of IC15 through to IC17 on issue V PCBs) to one of these threads but I think he prefers to remain a read-only member.
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Old 30th Jun 2019, 8:14 pm   #211
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
I don't know whether SOC would have ever have gone so far as to implement memory paging as suggested by Tim / tried by Tony, but they might and ought to have got to the point where the bus connections were all available at the edge connector (they did, after all, do this on the ZX80 onwards from the very start). They should have done it on the MK14 on the first issue which had contact fingers for the lower side of the rear edge connector, whichever issue that was.
I deduce that they must have from the promised BASIC board in the manual update letter as NIBL would have needed paging.

http://www.computinghistory.org.uk/d...Update-Letter/

The fingers are not in the Issue IV as I found a photograph of the bottom of one in the "Story of the Commodore 64 in Pixels". In the article on Archer Maclean he incorrectly attributes his to 1976 but the photo is quite clear:

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Quote:
If they'd done that (and with the unwanted PROM images already removed from issue V onwards) they could have introduced a 'RAM pack' PCB which plugged into the rear edge connector in the best tradition of Sinclair machines going forwards from that point, perhaps with an ongoing connector on its own rear edge, appropriately pinned out for the VDU via a DIN connector of the same type which the VDU was obviously laid out for. (Your third or fourth next project, perhaps...)
I had always intended getting to a memory board, again as described in the Update Letter, that perhaps even turned a right angle as well to make the final layout of the VDU go to the right so there was room for a 40 Key keyboard to the right of the board and below the now horizontal VDU putting the UHF/Composite out on the right. This could then contain a second connector for the NIBL board perhaps directly above it. Making the whole thing close to a single board machine of the time... and manageable on a normal desk!

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Quote:
Incidentally the same forum member who confirmed that the issue V did have those unwanted PROM images removed 'out of the box' also told me that there are still multiple images of the RAM I/O and display in the issue V memory map, so he then further modified his issue V machine to remove those images as well. I invited him to post details of the mods (in the area of IC15 through to IC17 on issue V PCBs) to one of these threads but I think he prefers to remain a read-only member.
Maybe they can provide them privately for you to present?
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Old 30th Jun 2019, 9:00 pm   #212
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Default Re: MK14 schematic revisions

Given that the MK14 issue 1 came out in 1977 and the ZX80 came out in 1980 I imagine any uogrades or further perripherals that SOC may have planned for the MK14 were canned in favour of the ZX80 which was a superior prospect for volume sales than the MK14. The Z80 processor had just dropped in price due to its widescale adoption in S100 machines, and even without the ZX81's ULA the chip count was only a little higher than the MK14!
While, from our perspective, it is a shame that SOC didn't produce the RAM upgrades, NIBL, ASCII keyboard etc it was clearly a wise decision because in one year of production before the arrival of the ZX81 it easily sold more than twice the number of units than the MK14 did in 3 years.
And then SOC/Sinclair took over the world with the Spectrum and looked unstoppable untill they produced the QL and... well the rest is history!!
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Old 30th Jun 2019, 9:17 pm   #213
Timbucus
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by Slothie View Post
Given that the MK14 issue 1 came out in 1977 and the ZX80 came out in 1980 I imagine any uogrades or further perripherals that SOC may have planned for the MK14 were canned in favour of the ZX80 which was a superior prospect for volume sales than the MK14. The Z80 processor had just dropped in price due to its widescale adoption in S100 machines, and even without the ZX81's ULA the chip count was only a little higher than the MK14!
From sources that sounds likely although according to this reference:

https://nosher.net/archives/computers/adve_075

The ZX80 was a U-turn where essentially Clive canned the BASIC version of the MK14, triggered the setup of Acorn who DID do a machine with BASIC on... and eventually lost the BBC contract

Quote:
While, from our perspective, it is a shame that SOC didn't produce the RAM upgrades, NIBL, ASCII keyboard etc it was clearly a wise decision because in one year of production before the arrival of the ZX81 it easily sold more than twice the number of units than the MK14 did in 3 years.
And then SOC/Sinclair took over the world with the Spectrum and looked unstoppable untill they produced the QL and... well the rest is history!!
Indeed it was the correct path for them (eventually) - in fact if you look at the ZX80 with the keyboard built onto the single board it is very much the missing link between the MK14 and the ZX81 and those that followed.

I quite liked the QL, it was very strange sitting on a train from Cambridge with a padded envelope with one in, among others with similar padded envelops not saying anything to each other, as we were all in fear of the massive NDA we had just had to sign!
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Old 30th Jun 2019, 11:57 pm   #214
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by Timbucus View Post

The fingers are not in the Issue IV as I found a photograph of the bottom of one in the "Story of the Commodore 64 in Pixels".
Actually, yes they are according to the evidence of the photo you attached

Maybe we aren't talking about the same thing, but I am referring to the contacts on the track / print side of the PCB for the rear edge connector. That issue IV PCB does have them although, as with the issue V, they aren't tracked to anywhere. My issue II PCB has no copper at all on the track side in that area, there are only contact fingers on the component side for the power, I/O port connections etc.

The manual for the VDU also says that on issue IV and V PCbs the connections for the VDU can be picked up from the rear edge connector: What it doesn't say is that you have to link the necessary signals to those contact fingers yourself.

Based on this, my assumption has always been that the track / print side contacts appeared from issue IV onwards, but I've never seen a good shot of the underside of an issue IV until now.

There is an added complication with respect to the forum member who provided the info about PROM images on the issue V - as far as I can make out he only visits the site incredibly infrequently. He may be the forum equivalent of Halley's comet.
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Old 1st Jul 2019, 12:42 am   #215
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
as far as I can make out he only visits the site incredibly infrequently. He may be the forum equivalent of Halley's comet.
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Old 1st Jul 2019, 7:38 am   #216
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Default Re: MK14 schematic revisions

Ha ha yes you are correct - Thank you for that. I was looking and thinking of the ones by the keyboard - which don’t appear in issue V either only Martin’s. Thanks for that - we just need an issue I and III image now.
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Old 1st Jul 2019, 11:57 pm   #217
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Default Re: MK14 schematic revisions

I also have to issue another correction - the picture was not from Archer's article in that book just checked - it is actually the one from:

http://www.old-computers.com/history...l.asp?n=37&t=3

Apologies I am slipping.
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Old 2nd Jul 2019, 12:29 am   #218
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Lightbulb Re: MK14 schematic revisions

Since you can solder a DIN 41612 a+b connector to the edge of the MK14, I'm very tempted to make a 3 or 4 slot "Motherboard" to plug into the top of the MK14 that will allow cards to be plugged in vertically. Thus you can have, for instance, the VDU, a 1.5k RAM/ROM module and other cards connected all at once. it might be required to have some kind of frame to support the cards, but in my experience the 41612 style connectors are pretty secure unless the card has some heavy components on it.
Just a thought.
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Old 2nd Jul 2019, 9:59 am   #219
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Default Re: MK14 schematic revisions

I may have a small number of the card support rails - if you look at any recent image or video clip of my MK14 you may notice that that is what holds my MK14 PCB in place in its plywood box by gripping the left and right edges.

The original PCBs gave no thought to how the board might ever be mounted in any sort of receptacle or on any surface, so the only holes through the PCB were those intended for the keypad rivets.

That's a thought, actually: Maybe the PCB could do with some strategically placed 3mm or 4mm holes with mounting posts in mind. Any nearby tracks would have to be steered away from them, though, to avoid the possibility of metal posts or screw heads making contact with tracks. Even if they are green coated, metalwork will bite through the coating eventually.
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Old 2nd Jul 2019, 6:44 pm   #220
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Default Re: MK14 schematic revisions

Well today's my birthday so I've treated myself to 5 new PCB's from JLCPCB. I did get a quote from PCBWAY and it was twice the cost! Maybe I didn't get some of the options checked right, but I found the UI confusing at first glance.
The new quote is remarkably cheap!
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