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Old 21st Mar 2020, 12:38 am   #321
DeltaAlpha52
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Default Re: MK14 schematic revisions

Interesting

I have been experimenting with 28c16 chips to see if they can be used in the Nascom, and apart from the first one I got being unresponsive, the second one seems to work. Just need to finish the coding to allow it to program the whole ROM.

I'll bear in mind the power issue - don't want to blow the arduino as well.
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Old 21st Mar 2020, 12:54 am   #322
Slothie
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Default Re: MK14 schematic revisions

I bought some of those and had no problems programming thrm with my TL866 programmer. It even worked on linux with Wine and a special replacement dll i googled for.
With any new-old-stock parts unworking parts are rather an occupational hazard unfortunately.
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Old 21st Mar 2020, 1:17 pm   #323
SiriusHardware
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Default Re: MK14 schematic revisions

When using the PROM reader sketch (which requires the UNO to be connected to a PC so that the serial connection can be used) the UNO will be running on power provided by the PC through the USB connection. I understand 'normal' USB has an upper current limit of 500mA allowed, so that's the absolute limit but the connection between +5V in on the UNO USB connector and the +5V out connection on the single row IDC female connectors is switched by an Si2301DS MOSFET.

The source and drain current capability of this device is above one Amp but its maximum power rating is quite low - not a problem as long as it is switched fully on and there is no volts drop across it since (any current) times (no voltage) = no Watts.

Obviously in the real world the device will have a small amount of 'on' resistance but it should be OK, I think, to draw 200mA through the PCB. If in doubt you could always provide the PROMs with a +5V supply of their own. For example, you could just temporarily tap the power for the PROMs from the +5V pin on the USB socket, bypassing the MOSFET.
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Old 21st Mar 2020, 9:49 pm   #324
DeltaAlpha52
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Default Re: MK14 schematic revisions

It works !!

Thanks for the Prom reader sketch - I used an Arduino UNO and checked the roms and they seemed to be fine. After that I used a data probe to check the data and address lines. All were pulsing like I thought they should until I came to address A7, took a bit of time to identify it, but A7 was being held low. No wonder it was not working.

The fault was where I had soldered the power connector wires and not cut the excess of the negative wire - in too much of a hurry to power it up and see if it worked . The negative wire excess bit underneath the board was short but long enough to connect to the A7 line next to IC3. It had worked okay until I had pushed the board down and that had pushed the wire onto the A7 line. I've removed the offending excess wire and now it is working again.

Ah well I've learnt a lot about the build of the MK14 whilst trying to fix this, now to put on a keyboard and look towards the automatic key entry attachment.

Cheers
time for
David
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Old 22nd Mar 2020, 12:39 am   #325
Slothie
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Default Re: MK14 schematic revisions

You always leatn more when things don't work, so I'm glad it didnt work and you diagnosed the fault!
Shorted address and data lines are a surprisingly commin fault, especially older gear that has seen enthusiastic maintenance, and not always easy to track down. Well done!
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Old 22nd Mar 2020, 10:18 am   #326
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Default Re: MK14 schematic revisions

Glad you got it sorted! Another one re-born.

Since you are obviously au-fait with Arduino you might like to consider trying to put together a keypad-entry uploader using one of those - (download intel hex to Arduino from PC via serial, Arduino then translates the received code into code entry keypresses).

Would be a good project to occupy you, now that you have a working MK14.
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Old 22nd Mar 2020, 10:25 am   #327
Slothie
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Default Re: MK14 schematic revisions

Spotted these switches on eBay that will fit my board and have transparent caps so theyll be easy to label neatly. I searched "tact switch 12x12" so you might be able to find them in colours other than green!

https://www.ebay.co.uk/itm/5-pcs-12-...p/382852459804
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Old 22nd Mar 2020, 11:16 am   #328
SiriusHardware
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Default Re: MK14 schematic revisions

I looked at the price and thought "Hmm" and then I looked again and saw how many you get for that price and thought .."Oh!". Since they are sold in lots of five, four lots will be exactly the number required.

Good Spot, thanks.
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Old 23rd Mar 2020, 6:04 pm   #329
DeltaAlpha52
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Default Re: MK14 schematic revisions

Quote:
Originally Posted by SiriusHardware View Post
Glad you got it sorted! Another one re-born.

Since you are obviously au-fait with Arduino you might like to consider trying to put together a keypad-entry uploader using one of those - (download intel hex to Arduino from PC via serial, Arduino then translates the received code into code entry keypresses).

Would be a good project to occupy you, now that you have a working MK14.
I have seen one of these in my wanderings over the net. I think the best one used optocouplers switches so as to not directly connect the MK14 and the other system.

Does sound like an interesting project now I'm not allowed out ( Daughter says got to do "Social Distancing" )

There was a separate video where someone had programmed a robot arm to press the buttons That might be going a bit too far.

Keep Well
David
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Old 23rd Mar 2020, 6:59 pm   #330
DeltaAlpha52
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Default Re: MK14 schematic revisions

Just found the entry on Vintage Computers "MK14 programming interface - MK2" by someone called "SiriusHardware"

Thank you for that. I know you used a Pi as the controller but I could look at using a Arduino maybe

Cheers
David
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Old 23rd Mar 2020, 7:29 pm   #331
SiriusHardware
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Default Re: MK14 schematic revisions

Yes, the more variations, the merrier.

The basic principle (as originally suggested by fellow forum member TonyDuell) is to use pairs of optocouplers to join keypad rows and columns together to electronically 'press' the keys. The attached diagram #1 illustrates it from the optocoupler output point of view. You activate one row opto and one column opto together, and that presses the corresponding key.

You can easily find 12 outputs to drive the leds of these optos individually (+1, if you want the interface to be able to reset the MK14) on an UNO. The main problem I was anticipating was how to create a big enough serial receive buffer for the incoming Intel Hex file on the UNO. I didn't really solve that problem in the short time I spent thinking about it.
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Old 24th Mar 2020, 9:09 am   #332
JohnBHanson
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Default Re: MK14 schematic revisions

I have written a device driver in z80 assembler that takes an intel hex file and drives an 8250 uart at 320 baud (it is clocked at 13*16*9600Hz.). This can be fed into the tape input of the mk14 and would only require one opto

All the routines are entered with register b the unit number and c the port address of the 8250.

Could be easily built into a program or used with my xbeaver emulator. I have also a program (masmx) which is part of the distribution which is an assembler for the mk14.

To build the driver use command:-
perform drvmac rt

to install in xbeaver

device install rt
device pun rt0
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Old 24th Mar 2020, 11:40 am   #333
SiriusHardware
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Default Re: MK14 schematic revisions

Just to clarify, I think John's contribution above exploits the uploading method suggested by Karen O in this now closed thread.

https://www.vintage-radio.net/forum/...d.php?t=154725
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Old 7th Apr 2020, 8:24 pm   #334
DeltaAlpha52
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Default Re: MK14 schematic revisions

Hi all

Well the MK14 from martin is up and running.

And thanks to the information supplied about a MK14 programming interface I built an interface board and it can now program the MK14. It is in 2 sections. The optical switches to connect to the MK14 and a separate board for the Pi Zero w. The reset is solder to the underside of the board and connects via a 2 pin plug.

I did have a couple of issues with one of the optical switches not working correctly. I think the problem seems to be that using 3.3v and 330r resistors one of the them was not getting enough juice to turn on. It worked when I tested it, before building the Pi interface, and the test system was nearer 5v. Think I'll use the 5v from the Pi to power the optical switches.

The other issue was speed. as was mentioned in the MK14 programming interface thread I had to slow the interface program down a bit to get reliable results.

But it's so much faster than having to type it in

Now to look at using an Arduino for the controller - problem with the Pi is it needs to be shutdown correctly where as an Arduino can just be turned off.

David
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Old 7th Apr 2020, 9:10 pm   #335
SiriusHardware
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Default Re: MK14 schematic revisions

I wish I knew why my Pi-Programmer seems able to run faster than anyone else's, but at least it works for you with a little bit of tuning up (or down). As far as I know mine is the only one which has been tried with an original MK14, and of course that is the machine I fine tuned the timing values with.

Mine has the original 80L95 IC rather than the 74LS365 which most people are using as a substitute - who knows what difference that may be making? Also, if you've fitted a 4.00MHz crystal rather than the original 4.43MHz, that will obviously make the MK14 run a little slower.

To be honest the choice of 330R series resistors for powering the opto LEDs from 3V3 was completely arbitrary, I've always used 330R for 3V3, 470R for 5V and 1K for 12V supplies without worrying too much about it - so by all means experiment for optimum performance.

My original incarnation of the keyboard-input programmer accepted an Intel Hex file input via a serial link from anything capable of sending a file out over serial, so in that sense it was more flexible and versatile than the current version. An Arduino based version would be the modern equivalent.

The main benefit of the Pi version is that it can also run a Linux text editor and a Linux compatible SC/MP assembler as well, thus allowing you to write SC/MP assembly language, assemble it and fire it out to the MK14, all from one working environment.
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Old 7th Apr 2020, 9:31 pm   #336
SiriusHardware
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Default Re: MK14 schematic revisions

I forgot to ask: How well does that replica keypad with the dome switches work?

It obviously looks really good, closer to original than any other replica I have seen, although the version available for the JM replica PCBs looks nice as well.
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Old 7th Apr 2020, 10:28 pm   #337
DeltaAlpha52
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Default Re: MK14 schematic revisions

The dome switches are working very well. It was the ones supplied by Martin. They are a pain to get right with 3 layers - 1 to provide a guide for the domes, 1 to stick the edges of the domes down and the final layer with the legends on. I struggled with it but finally got it stuck down and I'll let you know if there are any longer term issues.
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Old 7th Apr 2020, 10:48 pm   #338
SiriusHardware
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Default Re: MK14 schematic revisions

To be honest, having experienced the horror of the original early version MK14 keypad which used a large conductive rubber mat rather than dome switches, I don't think I would ever put anything less than real switches on a replica. However there's no denying that the 'Martin' replica with that nice re-manufactured keypad overlay is by far the most authentic looking of the replicas.

Couple of other things - One, I assume (since you did not say otherwise) that the keypad edge connector connection layout is as per original MK14s, and not as per the JM PCB which has a different, (arguably more sensible) layout?

Second thing: Would you mind using the monitor to look at the contents of address 0000, 0200, 0400 and 0600 and let us know whether the contents of 0200, 0400 and 0600 are...

-The same as 0000?
-Different to 0000?

As far as we know the 'Martin' replica is an exact clone of the original issue V PCB. If it is, the 'unwanted' PROM images which are present at 0200, 0400 and 0600 on earlier MK14s should be absent on your machine. If they are absent that's good because it means the way is clear for you to map something else (memory, more I/O, etc) into the address space at 0200-07FF. On earlier issues, the PCB has to be hacked about in order to remove those unwanted PROM images before you can start mapping things into that address range.
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Old 7th Apr 2020, 11:27 pm   #339
DeltaAlpha52
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Default Re: MK14 schematic revisions

I can see the benefits of using the Pi when developing code. Which assembler as you using - is it The SB-Assembler 3?
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Old 8th Apr 2020, 12:07 am   #340
SiriusHardware
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Lightbulb Re: MK14 schematic revisions

Quote:
Originally Posted by DeltaAlpha52 View Post
Which assembler as you using - is it The SB-Assembler 3?
Yes, that's the one. As with almost any assembler, the code in the MK14 manual requires a certain amount of 'Syntax conversion' before SBA3 can assemble it.
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