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 24th Aug 2018, 9:51 am   #21
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Replica MK14 PCBs

I asked the same question myself and was pointed to this:

https://preview.ibb.co/ifKgZ7/mk14_v5.jpg

If your issue V is working, it would be great if you could try the following brief test:

Look at the first few bytes of the OS (0000H... onwards)

Then, see if you can also see those OS bytes at

0200H... on,
0400H... on,
and
0600H... onwards.

If you can, then the address decoding on the issue V is as it was on earlier issues, but if you can't, then the address decoding has been cleaned up to leave a 'hole' from 0200-07FF into which you can map something else, in most cases more RAM.
SiriusHardware is offline  
Old 25th Aug 2018, 12:33 pm   #22
GrahamN
Hexode
 
Join Date: Jun 2008
Location: Burnham on Crouch, Essex, UK.
Posts: 391
Default Re: Replica MK14 PCBs

Thanks to Graham (SiriusHardware) who programmed my PROMs for me, I now have a replica MK14 made with a JMP circuit board.
Attached Thumbnails
Click image for larger version

Name:	MK14.jpg
Views:	135
Size:	118.0 KB
ID:	168049  
GrahamN is offline  
Old 25th Aug 2018, 9:16 pm   #23
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Replica MK14 PCBs

The keypad looks very smart, is that something available from one of the retro outlets or did you make the overlay yourself? I assume there are tact switches underneath it?
SiriusHardware is offline  
Old 25th Aug 2018, 9:27 pm   #24
GrahamN
Hexode
 
Join Date: Jun 2008
Location: Burnham on Crouch, Essex, UK.
Posts: 391
Default Re: Replica MK14 PCBs

It came from JMP, the same as the PCB. The switches are a bit larger than tact switches and are the same as the reset switch, but without the cap. I bought the switches from Germany as they were a better price than I could find in the UK and originally I intended to use white caps similar to the cap on the reset switch, but was offered a 3D printed panel at a good price, so changed my mind at the last minute.
Attached Thumbnails
Click image for larger version

Name:	IMG_4061-1600.jpg
Views:	88
Size:	125.3 KB
ID:	168085   Click image for larger version

Name:	IMG_4062-1600.jpg
Views:	74
Size:	105.3 KB
ID:	168086  
GrahamN is offline  
Old 25th Aug 2018, 9:47 pm   #25
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Replica MK14 PCBs

Very nice, if only SOC had managed to come up with something as decent as that in the first place.

I see you've even managed to find yourself a INS8154 RAM/IO IC as well, so you now have the RAM expanded to a dizzying 640 bytes. Luxury!

Last edited by SiriusHardware; 25th Aug 2018 at 9:54 pm.
SiriusHardware is offline  
Old 26th Aug 2018, 8:06 am   #26
GrahamN
Hexode
 
Join Date: Jun 2008
Location: Burnham on Crouch, Essex, UK.
Posts: 391
Default Re: Replica MK14 PCBs

The RAM chip wasn't cheap! But it would have driven me mad looking at the empty socket if I hadn't got it.
GrahamN is offline  
Old 26th Aug 2018, 11:40 am   #27
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Replica MK14 PCBs

Looking around at images of original MK14s on the 'net, a lot of them never did get fitted with one. I bought mine from Tandy, believe it or not. Tandy sold a lot of useful ICs, always with the data sheet included, back in the day. I suspect they stocked the INS8154 specifically with MK14 owners in mind, as it was never really a mainstream / widely used parallel port IC like, say, the 8255.

If you intend to actually play with the machine rather than just own it, the extra 16 lines of I/O provided by the RAM I/O greatly increase its 'play value'. You can hook up a generic 2-line alphanumeric LCD display to one port (use the display in 4-bit data mode, using three of the remaining bits for the RS, RW and EN control lines) and that still leaves the other 8-bit port free for general use.
SiriusHardware is offline  
Old 26th Aug 2018, 1:01 pm   #28
GrahamN
Hexode
 
Join Date: Jun 2008
Location: Burnham on Crouch, Essex, UK.
Posts: 391
Default Re: Replica MK14 PCBs

Are there any good books about the MK14? As far as I can see there is the manual, an unobtainable book "understanding microprocessors", and that's about it. I would quite like to actually understand the computer rather than just let it sit on a shelf.
GrahamN is offline  
Old 26th Aug 2018, 2:01 pm   #29
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: Replica MK14 PCBs

The 'Understanding Microprocessors' book is the only one I'm aware of and I never saw a copy. As you say, it seems even harder to come by than an actual MK14.

The authors are both trustees(? heavily associated, anyway), with the Centre For Computing History near Cambridge, which has a reference copy of the book in its collection. I was considering writing to them c/o the museum to ask whether they would considering putting it into the public domain, or releasing it as an e-book via the usual sources, given the sudden increase in all things MK14 related. For anyone able to visit, I understand they also have not only a pristine example of an MK14 but also an extremely rare unbuilt kit, as well as Ian Williamson's unique original prototype of the MK14.

In 1977/78 an MK14 was the most likely 'computer' that many people were likely to possess, with 'proper' systems costing a great deal more, so despite its simplicity the MK14 was quite well supported in the hobby electronics press with articles about hardware add-ons and useful bits of code. Unfortunately I didn't have many of those to start with and have none now. I think Practical Electronics was one of the magazines which often had bits about the MK14 in it, so if you can find an archive of PE magazines circa 1977-1980 try having a look through those (and let me know if you find anything useful!).

The MK14's own manual has been criticised in some quarters as not being very good for absolute beginners, which of course we all were in those days. I muddled through because I had already had a bit of experience programming a friend's SC/MP based system (which had been a project in Elektor magazine). That system used binary switches for address and data entry and individual LEDS to indicate the address and data, so when the MK14 finally arrived (very late, as Sinclair stuff always did) it seemed like a Rolls-Royce by comparison... until I realised how bad the keypad was.

It wasn't long before the keypad was replaced with something better, and that is why so few MK14s survive with their original keypads intact.

If you want to make your life easier, try finding an SC/MP (8060) cross assembler to run on your PC platform of choice. This is an option we didn't have back in the day, but it makes writing MK14 code now much easier.

There are also various possible schemes for transferring assembled code into the MK14 rather than having to type it in. It's a good idea to try to organise something like that because the MK14, of course, forgets everything you have typed into it the moment you power it off, so you really need some way to load your already written code back into it next time you turn it back on.
SiriusHardware is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 10:45 pm.


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.