UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Computers

Notices

Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

Closed Thread
 
Thread Tools
Old 2nd Dec 2020, 2:21 am   #601
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: MK14 schematic revisions

Not all of the address blocks are 512 bytes. The RAM is in 256-byte chunks and the I/O RAM fits into two 128-byte blocks.

I'm not aware of any documentation for the Williamson prototype but if you are ever back in England and in or near Cambridge you can see his MK14 prototype displayed as part of a small but impressive MK14 collection at the Centre For Computing History (Not to be confused with the National Museum Of Computing, which is based on the Bletchley Park site near Milton Keynes).
SiriusHardware is offline  
Old 2nd Dec 2020, 3:15 am   #602
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: MK14 schematic revisions

Each set of RAM occupy 512 bytes and the 8154 occupies 1024 bytes though the shadow image of each is not adjacent blocks of 256.

As the Ram and 8154 both have two select inputs they could be arranged to only occupy 256 bytes of address space using a bcd to decimal decoder, though possibly not if one of the RAM blocks has to be at 0xF00-0xFFF to allow reuse of rom from the introkit and keyboard kit.

Any chance we can sneak one of Slothie’s VIs into the museum?
Mark1960 is online now  
Old 2nd Dec 2020, 12:12 pm   #603
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: MK14 schematic revisions

There may be something in that, for there to be a modern reproduction to be put in the display but there are pros and cons for each one.

The Czech 'Martin L' clones are the closest in terms of aesthetic appearance, especially with the nicely reproduced membrane keypad, so should it be one of those?

Or should it be one of MK14man's re-done ones using modern components / programmable logic, from a few years ago - that would be the most obviously hi-tech 'modern' copy, and they do look very nice.

To me, the issue VI is the user's choice, the one you choose if you actually mean to play with it and not just look at it, so it would be a terrible waste to put one of those in a museum.

While thinking about it, surely one of Karen's PIC14s should also go into the display? But then again, I suspect she would rather have seen them all being used rather than stuffed and mounted in a museum.
SiriusHardware is offline  
Old 2nd Dec 2020, 1:12 pm   #604
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: MK14 schematic revisions

I think back in '78 if I was designing it I would have used a 3-8 decoder (or 4-10, whichever was cheaper) although its feasable back then 3 logic chips were cheaper than 1 7441 wholesale. Sinclair was well known to use whatever he could get cheap on the wholesale markets in his products, which to be fair to him was how he was able to push out his products at half the price of his competitors. I have read somewhere that in his early days producing hifi modules he would get reject batches of transistors and individually test them to find the "good" ones (a process not dissimilar to what I suspect happens on eBay to this day). As for the design of the MK14, isn't it just a copy of the introkit? I saw this diagram of the "keyboard kit" that clearly shows 74157s being used as latches, so SoC clearly just copied what National showed them...
Attached Thumbnails
Click image for larger version

Name:	SC_MP Keyboard Kit Schematic.jpg
Views:	75
Size:	126.1 KB
ID:	221660  
Slothie is offline  
Old 2nd Dec 2020, 4:29 pm   #605
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: MK14 schematic revisions

I could be wrong but I think Nat Semi both designed and supplied the kits, so it was hardly surprising if it was just a redesigned National Introkit + keypad and display all on a single PCB.

If so, we MK4teenies had it easier than the Introkit guys who had to build their optional keypad / display interface on a 'matrix' section of the Introkit PCB using wire-wrapped interconnections.
SiriusHardware is offline  
Old 2nd Dec 2020, 5:09 pm   #606
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: MK14 schematic revisions

Maybe in 78 a decoder would have been the obvious choice but just a few years earlier the basic gates might have been cheaper for the introkit. Then the same design was copied for the mk14.

I think the introkit might have used a bytewide mask rom instead of 4 bit prom, while the mk14 took what seems to be a backward step to 4 bit wide prom. Maybe this is also due to the later introduction of the mk14, perhaps the rom was no longer in production and cost of another production run was too high and long lead time.

From the photos in theregister article the introkit also used 22 pin 2101 ram, so probably a cost reduction to change to 16 pin 2111. The address decoding on that looks to be much fewer chips than the mk14, at least on the introkit part of the circuit but then the mk14 added another set of ram and the 8154.

I found it interesting that theregister article says Ian Williamson still has the prototype in his loft with the cambridge calculator, while the centre for computing history claims to have the prototype given to sinclair. Most likely this was a second build demo unit.

The original Ian Williamson design was very different, using octal and using the calculator chip to drive the display. That would make it very difficult to source parts for a replica now.

I wonder if the PIC14 could be made suitable for offering as a kit in the centre for computing shop?
Mark1960 is online now  
Old 2nd Dec 2020, 5:49 pm   #607
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: MK14 schematic revisions

Quote:
Originally Posted by Mark1960 View Post
I wonder if the PIC14 could be made suitable for offering as a kit in the centre for computing shop?
It would make a better exhibit than mine tbh.
Slothie is offline  
Old 2nd Dec 2020, 5:59 pm   #608
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: MK14 schematic revisions

Oh I Read that wrong... yes, a kit on those lines would be a brilliant idea.
Slothie is offline  
Old 2nd Dec 2020, 7:15 pm   #609
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: MK14 schematic revisions

Karen always made her hobby projects freely available to all but it's highly unlikely that freedom was intended to extend as far as anyone selling kits derived from her work - although TCFCH would undoubtedly plough any funds thus generated straight back into the museum.

Pilouphat83 did have some PIC14 PCBs made but he kindly gave all his spares away to interested parties, which was obviously in keeping with the spirit of Karen's original intent.

TCFCH did once have a few interesting kits in their shop / online shop but by the time of my first physical visit to the museum last year most had been sold out and not replenished. I do remember one of the kits was functionally similar to the original Introkit, in so far as it needed to be communicated with via a terminal.

Unfortunately they've recently had a major flood due to a burst pipe, but as far as I remember most of their exhibits are off the floor so hopefully they didn't lose too much.
SiriusHardware is offline  
Old 2nd Dec 2020, 10:29 pm   #610
Timbucus
Octode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 1,362
Default Re: MK14 schematic revisions

For those who are interested in seeing Williamson with his kit at this point in his video he talks about how it came to be...

https://youtu.be/awlqzippsSc?t=3615

I am sure we could have a word with Karen's estate if we thought a kit that went to the museum with a contribution to maybe a cancer charity and would prove popular. Williamson is a trustee of the museum and what would be great, is if we he could be pursuaded to get his book in reprint as an accompaniment... I would love a copy.

Here are some shots I took of it when I was last there as well.

Click image for larger version

Name:	IMG_1658.jpg
Views:	86
Size:	57.0 KB
ID:	221713Click image for larger version

Name:	IMG_1660.jpg
Views:	84
Size:	69.0 KB
ID:	221714
Timbucus is offline  
Old 2nd Dec 2020, 10:44 pm   #611
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: MK14 schematic revisions

That saves me from hunting around and finding mine. Imagine, wire wrap was once 'a thing'. Thankfully, I only ever got involved with that once, and not on something I built.

Everything else the museum sells in its shop is to raise funds for the museum, which is itself a charity, so there would be a potential conflict of interest there.
SiriusHardware is offline  
Old 2nd Dec 2020, 11:05 pm   #612
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: MK14 schematic revisions

I never made a wire wrap board, but my Dad found a load of wire wrapped circuit boards from an early mainframe which I stripped down and got a load of transistors from - bearing in mind back then a single transistor was about 30p which is £3.50 in todays money so it represented a huge bargain! Most of my early transistor experiments were with anonymous american transistors that had metal cans and colour coded insulated leads.... (red green and white if I recall correctly). We built a transistor tester to test them which was from a plan in Radio Constructor and used rotary switches and an ammeter we salvaged from old war surplus radio equipment (no doubt others on this board will faint at the heresy of scrapping them, but back then you couldn't move for old military equipment).
Slothie is offline  
Old 3rd Dec 2020, 12:27 am   #613
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: MK14 schematic revisions

The SC/MP and 8154 in my issue VI (swinging neatly back on topic) came from a very old standalone EPROM programmer which I was given perhaps 15 years ago. It was complete and working, although very battered. I mercilessly scrapped it just for those two ICs, and even then only as spares for my one and only MK14.

I would faint at the thought of doing that now - there was no reason not to keep it completely intact with the two ICs still in it knowing that I could always remove them for the MK14 if that was ever needed.

In my defence, I already had two PC-driven EPROM programmers which were much more powerful / had vastly greater device support lists than the old programmer but at the time I didn't consider its historical importance. It was probably about the same age as the MK14, give or take a couple of years.
SiriusHardware is offline  
Old 3rd Dec 2020, 4:26 am   #614
circuitryboy
Pentode
 
circuitryboy's Avatar
 
Join Date: Jun 2012
Location: Bristol, UK.
Posts: 115
Default Re: MK14 schematic revisions

There's been a lot of topic oscillation in this thread and I missed the moment it swung over the Williamson SC/MP board, which has always been of interest to me.
As we know, it was not "the prototype of the MK14" but it did bring the SC/MP processor to SoC's attention and MK14 was the result.
What scuppered the Williamson was the (ingenious!) way it overrode the IC in a Sinclair Cambridge calculator to use it for keypad and display. But it was a decimal calculator; so to enter, say, "C4 0F" you had to mentally convert to "304 017". Not a selling point.
circuitryboy is offline  
Old 3rd Dec 2020, 8:36 am   #615
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: MK14 schematic revisions

Quote:
Originally Posted by circuitryboy View Post
There's been a lot of topic oscillation in this thread and I missed the moment it swung over the Williamson SC/MP board, which has always been of interest to me.
As we know, it was not "the prototype of the MK14" but it did bring the SC/MP processor to SoC's attention and MK14 was the result.
What scuppered the Williamson was the (ingenious!) way it overrode the IC in a Sinclair Cambridge calculator to use it for keypad and display. But it was a decimal calculator; so to enter, say, "C4 0F" you had to mentally convert to "304 017". Not a selling point.
I think it would be interesting to learn more about that original prototype and how it worked, maybe in a new thread would be better.

Its probably not a case of converting between hexadecimal and octal, just a matter of learning to think in octal, similar to how we had to learn to think in hex. I remember with the pdp11 it was more common to see machine code and low level data in octal, still commonly used in file permissions in unix. Z80 machine code also probably becomes more readable in octal but we have just become so accustomed to reading hex.
Mark1960 is online now  
Old 3rd Dec 2020, 12:32 pm   #616
TonyDuell
Dekatron
 
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,190
Default Re: MK14 schematic revisions

The PDP11 machine code instructon set is generally a lot easier to understand in octal than in hex. For a 2-operand instruction, it's 4 bits (first 2 octal digits) for the operation, 3 bits (next octal digit) for the source addressing mode, 3 bits for the source register, 3 bits for the destinaton addressing mode and 3 bits for the destination register. So in octal each digit can be understood separately. For a similar reason VAX machine code is clearer in hex.

I seem to remember that unix permissions are again in groups of 3 (Write, Read, Execute) so octal is natural there too.

And yes, the 8080 and thus the Z80 instruction sets are clearer in octal a lot of the time. My Intellec MCS8i (8080-based) has lines grouping the data switches on the front panel in groups of 2,3,3 for that reason. I guess it just didn't catch on.

I'm not so sure about the SC/MP instuction set though. Looking down the datasheet there's little to choose between using hex or octal (things like the pointer register to use are the 2 LSB's of the instruction) but I think hex is slightly simpler.
TonyDuell is offline  
Old 3rd Dec 2020, 2:20 pm   #617
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: MK14 schematic revisions

Looks like I'm running out of excuses not to put together my MK14 thanks to Mark!
Attached Thumbnails
Click image for larger version

Name:	MK14chips.jpg
Views:	78
Size:	85.8 KB
ID:	221747  
Slothie is offline  
Old 3rd Dec 2020, 6:39 pm   #618
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: MK14 schematic revisions

Anything else you still need?
SiriusHardware is offline  
Old 3rd Dec 2020, 7:00 pm   #619
Slothie
Octode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 1,287
Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
Anything else you still need?
No.... I think I have everything. I'm using a 28C16 rather than the PROMs for now, I have some PCBs coming from china to make an adaptor. This will also make it possible for me to experiment with firmware in the future, sooner or later when I get my stuff I will make a PROM programmer and make myself some proper ones!
Fortunately the displays, power connector, regulator etc I have left over from the PIC14 will be good, and a few months ago I got a set of keys that I happened across on eBay. So I think I'm OK! I'm going to try to make some documentation as I go along too.
Slothie is offline  
Old 3rd Dec 2020, 9:13 pm   #620
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: MK14 schematic revisions

I’ve just about finished a pcb layout for a pair of adapters to use 2732, in a panel of two to be separated by hacksaw to avoid paying for two separate boards. I thought it might be slightly easier to program two eproms with the full 8 bits with slightly different wiring in the adapter for high and low nibbles.

Aiming to place an order with jlcpcb next week for a set of your v1.2 boards, probably in blue, and a couple of other boards that I have had ready to go for a few months.

I have everything else on the way including another display instead of asking my mum to send the batch I had delivered to the uk from the netherlands last year. Also ordered a set of individual digits as a backup before I saw that groups of four are cheap from lcsc. Still missing the strip to mount the display but I’ll probably use header pins.

I found the 12x12 tactile switches with white caps and clear covers on amazon and nearly missed that you used a different reset switch but found a set of twenty on ebay that look similar to the switches on my MK14 IV.
Mark1960 is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 3:34 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.