UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio 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.

Reply
 
Thread Tools
Old 20th Dec 2018, 10:13 am   #141
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,734
Default Re: MK14 schematic revisions

Quote:
Originally Posted by Slothie View Post
My concern other than availability would be that the BPROMs may not be fast enough when its access time is added to that of the RAM and Monitor ROM, but that would be something that would be easy enough to try out, and would make fully expanding the MK14 to 512b prom + 3k RAM possible, and would make many more complex VDU projects feasable (Like MK14 space invaders ??!!)
Don't get too ambitious, the dot resolution of the VDU in graphics mode is not terribly high. 'Pong' might be a more realistic aim.

BPROMs were used on the Nascoms, or at least one of them, as custom address decoders. They are actually surprisingly fast in terms of access speed - for that reason they were often used in things like video test pattern generators where the access speed of contemporary EPROMs might have been too slow.

However, as with all things that age they are becoming more expensive and difficult to get. GALs would be another option but only a small percentage of people have programmers capable of programming them. The parts would really need to be as ubiquitous as possible. A 'modern' fast EPROM might work just as well as an address decoder but it would come in a wide bodied footprint.
SiriusHardware is offline   Reply With Quote
Old 20th Dec 2018, 1:00 pm   #142
Slothie
Pentode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 110
Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
However, as with all things that age they are becoming more expensive and difficult to get. GALs would be another option but only a small percentage of people have programmers capable of programming them. The parts would really need to be as ubiquitous as possible. A 'modern' fast EPROM might work just as well as an address decoder but it would come in a wide bodied footprint.
GALs might be an option; my cheap 50 TL866CS/Minipro programmer will do Lattice GAL16V* and GAL20V* and Minipro works great on Linux under Wine with a modified DLL. Although obsolete too they seem to be far more available than BPROMS. Although I've never used GALs I have used CPLDs which are much the same. I'd have to find some logic compiler to generate the bitmap that the Minipro expects but I'm sure there's something out there for free. (Sadly the TL866 doesn't do BPROMS )

That said, if someones kitted themselves out with a programmer for Tesla PROMS for the monitor then programming an address decode PROM wont be an issue! eBay seems to be flooded with Tesla 74S571s at the moment, so perhaps I should get my act together and start looking at programming them!
Slothie is offline   Reply With Quote
Old 20th Dec 2018, 1:02 pm   #143
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,734
Default Re: MK14 schematic revisions

.... nudge.
SiriusHardware is offline   Reply With Quote
Old 25th Jan 2019, 1:34 pm   #144
Slothie
Pentode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 110
Default Re: MK14 schematic revisions

Hmm things are getting a bit tight....
Attached Thumbnails
Click image for larger version

Name:	Screenshot_2019-01-25_12-29-46.png
Views:	49
Size:	24.6 KB
ID:	177088  
Slothie is offline   Reply With Quote
Old 25th Jan 2019, 6:48 pm   #145
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,734
Default Re: MK14 schematic revisions

Project impossible? (Within the established footprint, at least). Maybe that's why S.O.C. never did it despite it being the obviously right thing to do.
SiriusHardware is offline   Reply With Quote
Old 26th Jan 2019, 6:22 am   #146
Slothie
Pentode
 
Join Date: Apr 2018
Location: Newbury, Berkshire, UK.
Posts: 110
Default Re: MK14 schematic revisions

Probably not impossible if i'm prepared to rip up and re-lay some tracks. It would have been far more difficult for SOC without modern CAD tools, the board photos I've seen show they were most likely done with tape and transfers on acetate sheets by hand, so yes that's probably why SOC didn't. I haven't quite given up yet
Slothie is offline   Reply With Quote
Old 28th Jan 2019, 8:10 pm   #147
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,734
Default Re: MK14 schematic revisions

I've just been looking around for maybe one or two pairs of spare DM74S571 PROMs to give me the option of occasionally using the MK14 for a dedicated purpose every once in a while - the price of Tesla PROMs has gone up to about 2+ 3 each and the seller I bought two 'real' (National Semiconductor) DM74S571 PROMs from for 6 each last May is now selling them for 16 each.

Elsewhere I found someone offering programmed pairs of PROMs for well in excess of 30 which I thought was ridiculous until I saw the price the DM devices are going for now (The devices being offered in that particular case are actually DM, not MH).

In the past, it was the price of original machines and the lack of availability of PCBs which held people back from building / owning MK14s. Before long it is going to become impossible for anyone to afford the parts to populate one. I can see a situation where eventually genuine MK14s in poor condition are being robbed for their parts to populate replicas or just to sell separately.
SiriusHardware is offline   Reply With Quote
Old 31st Mar 2019, 2:49 pm   #148
Timbucus
Tetrode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 51
Default Re: MK14 schematic revisions

I can certainly vouch that the cost and difficulty of sourcing parts for a replica is rising, glad I am doing it now.

Just like to say thanks to all of you for the amazing amount of discussion on here around this little device. I am in the process, with the various signposted resources in the threads, of building at least one (as often I order two of something when the postage is the significant bit) based on a JM (Issue 0) board I bought, little did I realise how much time and money completing it would cost... and how much a mistake on the first key order would add, when the needed ones are no longer produced and therefore even more expensive - they are Multimec 3FTL6 or H9 as that is not documented elsewhere - they are hidden until the red keycap and the reproduction keypad housing.

I have not yet heard back from Martin on getting some pre-programmed PROMS but, I have included 2 on my order along with the 8060 and 8154 - if they turn out to be original (and blank...) DM then I would obviously need to find someone who can program them for me. Even better a pair of the Tesla ones which I have, although I read in other threads are proving difficult to find / create a programmer for...

I attach a photograph of the board so far - there appear to be no shorts between any data or address lines etc and 5v/Gnd is correct on the sockets but, I can do little more until my CPU, RAM and programmed PROM's arrive. The connector at the top was a way to connect power and to build the Single step circuit / have dupont access to the I/O connections. I also have the parts on order to make the clever keyboard / PI programmer from SiriusHardware as I am sure I will get tired of the hex data entry...

The display is a modern one which I gave into as I did not have the heart to rip apart the Text880 I bought, as it still actually works...
Attached Thumbnails
Click image for larger version

Name:	Timbucus.jpg
Views:	36
Size:	64.5 KB
ID:	180660  
Timbucus is offline   Reply With Quote
Old 1st Apr 2019, 12:00 am   #149
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,734
Default Re: MK14 schematic revisions

Welcome Timbucus, nice to have another potential MK14 user on the forum. As you may have read elsewhere, if your PROMs turn out to be blank National Semiconductor (DM prefix) parts then I can program them for you - all I ask is a stamped, addressed jiffy bag to send them back in. PM me if / when you get to that point.

There are at least two forum members who are intending to make stand-alone, possibly Arduino based programmers to handle the Tesla versions but those projects have not, as far as I know, come to fruition yet. Unfortunately, real life tends to get in the way.

For my project to build Karen O's PIC14 hardware MK14 emulator, I bought a Texet 880 which was honestly advertised as having one broken key (and therefore very cheap), so I didn't feel too bad about removing the display from it - but I did it in a non destructive way and kept the rest, so it could be restored at some point.

As to sourcing other parts, it's possible that some forum members who have already trodden this path may already have bought more parts than their replica needed, either because they were sold as a lot or to make the postage a more reasonable fraction of the cost. If you can let us know of any outstanding parts you still need, maybe someone may have some surplus to requirements which they would like to move on to offset the cost of their own replica.
SiriusHardware is offline   Reply With Quote
Old 1st Apr 2019, 7:32 pm   #150
Timbucus
Tetrode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 51
Default Re: MK14 schematic revisions

Thank you very much for the warm welcome and the offer to blow the PROM's! Fingers crossed.

My 2111 chips arrived today - when I looked I had only one in my electronics collection (hoard from attic), which was not MM. Also didn't have most of the other 74 series either despite a fair range...

I did however have some offcuts of connectors including a single sided 15way that if I miss Pin 1 (as 2 is also 0v) will work for the Keyboard programmer... by luck Pin six was the Keyway which I don't need connected...

I will reach out if any further bits are needed.
Timbucus is offline   Reply With Quote
Old 2nd Apr 2019, 12:23 am   #151
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,734
Default Re: MK14 schematic revisions

OK, let us know how you get on. (As a new forum member your posts are currently subject to new user moderation / delay. After a few more posts that will wear off and you will be able to post in real time).

The connectors I currently have on my MK14 (rear edge and keypad connector) were bought around 2012 from RS, and are both exactly the right length, single sided with no keyway - it's almost as though they originally stocked them with the MK14 in mind and still had some stock left all that time later.

I'm not sure if they still do them now though, and even if they do, they were tremendously expensive 6-7 years ago, never mind now.

Edit: On a quick look, they still do the 32-way version - note that although it looks double sided in the illustration the upper and lower contacts are paired so there are only 32 pins sticking out of the rear of the connnector. Not so useful for those of you who have late issue MK14s which do have double sided rear edge connectors. Here they are - the keys in the outer ends (position 0 and 33) are removable.

https://uk.rs-online.com/web/p/edge-connectors/0466551

... but look at the price! They might even still do the 16 way one as well, I did not look that far.

Last edited by SiriusHardware; 2nd Apr 2019 at 12:51 am.
SiriusHardware is offline   Reply With Quote
Old 2nd Apr 2019, 7:59 pm   #152
Timbucus
Tetrode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 51
Default Re: MK14 schematic revisions

Nice looking connectors, but, not so nice on the price. I again was lucky as I had a 80 way that I cut down to make the one in the photograph. That leaves enough for another one as well - aren't junk boxes great - my Dad was a real hoarder as well so I have the benefit of over 60 years of useful electrical bits - I think I may dispose of the Capacitors though as they were cheap bags in the late 70's... Some of the bigger ones look too cool so maybe I will keep them for decorations.

Also I finally have the MK14 board fully populated and the CPU etc arrived with REAL DM chips - no idea if they are blank so I think a PM to Mr SirusHardware is in order to a) take a look and b) program them if so. If not I wonder what is on there?
Timbucus is offline   Reply With Quote
Old 2nd Apr 2019, 9:17 pm   #153
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,734
Default Re: MK14 schematic revisions

Yes, I got your PM, you have one by way of return. Let's hope those devices are both genuine and blank.
SiriusHardware is offline   Reply With Quote
Old 2nd Apr 2019, 10:08 pm   #154
Timbucus
Tetrode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 51
Default Re: MK14 schematic revisions

Indeed let's hope they are genuine and blank, they are marked (and from what seems to be a professional source) DM74S571N so will be winging their way to you. Thank you very much!
Timbucus is offline   Reply With Quote
Old 9th Apr 2019, 6:59 pm   #155
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,734
Default Re: MK14 schematic revisions

(Keeping the more general MK14 related questions in this thread).

Timbucus: regarding your suspected faulty INS8154, RAM/IO IC, how did you come to that conclusion?

The RAM/IO has three 'images' in memory at 0800 onwards, 0C00 onwards and 0E00 onwards. For the purposes of this, let's stick with the one at 0800 onwards.

The 128-byte RAM portion of the device is mapped into the upper half of the 256-byte block occupied by the RAM/IO, therefore at 0880-08FF. You should find that data entered anywhere within that address range will 'stick'.

If you tried it out by editing addresses low down in the RAM/IO block and expecting them to read back the same, 0800 - 0824 are the control / data registers etc of the I/O portion of the device, so writing to those locations and then looking at them would give unexpected results.

Addresses 0x0825-0x087F do not (officially) have any hardware associated with them, so anything written to that range would be lost.
SiriusHardware is offline   Reply With Quote
Old 9th Apr 2019, 8:12 pm   #156
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,734
Default Re: MK14 schematic revisions

A quick test for the I/O section of the INS8154 IC just using the monitor - assuming the new / improved monitor is in use.

First,

Code:
Abort
0 8 2 3
Term
F F
Mem
You won't see the data digits change, but doing this writes FF to the port 'B' data direction register to define all of the port B pins as outputs.

Then,

Code:
Abort
0 8 2 1
Term
5 5
Mem
This time, you will see the data digits change. This writes the pattern 01010101 to the port pins 0-7 of port B. You should be able to verify this with a meter, scope or logic probe.

Finally,
Code:
Abort
0 8 2 1
Term
A A
Mem
Should write the pattern 10101010 to bits 0-7 of port B.

I chose port B for this because the port pins 0 through to 4 appear in a sensible order on the edge connector. The port A pins are all over the place.
SiriusHardware is offline   Reply With Quote
Old 9th Apr 2019, 9:44 pm   #157
Timbucus
Tetrode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 51
Default Re: MK14 schematic revisions

Well I just got in from dinner and was going to slob - saw your messages and went DUH as I had tried lots of addresses in 0800 for 128 bytes- didn’t notice the 0880 thanks - works fine and I can toggle the io port B lines fine with your script according to a meter - appreciate the help can’t believe I was so dull... and I didn’t even need to turn on my PC as I had printed out lots of useful diagrams and sheets for the MK14 so had the pinout.
Timbucus is offline   Reply With Quote
Old 9th Apr 2019, 9:47 pm   #158
SiriusHardware
Nonode
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 2,734
Default Re: MK14 schematic revisions

One less problem.
SiriusHardware is offline   Reply With Quote
Old 9th Apr 2019, 10:05 pm   #159
Timbucus
Tetrode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 51
Default Re: MK14 schematic revisions

Indeed thanks again for the pointers - I also added my last two RAM chips and they seem to work so I have a full 640 bytes, almost as much as my first kit built machine the ZX81... I can try segtris now yay!
Timbucus is offline   Reply With Quote
Old 11th Apr 2019, 2:16 pm   #160
Timbucus
Tetrode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 51
Default Re: MK14 schematic revisions

I have discovered why I thought the 128 byte IO RAM is at 0800 - it seems the memory map (which I have been using) on the online emulator is wrong...

http://www.dougrice.plus.com/dev/seg_mk14.htm

I cannot get the virtual machine to respond well enough to test if it actually implements it wrong - something with the browse speed on my PC I expect.

Looking at Page 52 of the V2 manual it is of course broken down as you pointed out.
Timbucus is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 10:35 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 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.