Re: MK14 schematic revisions
 

That sounds like a good find for the price. I think the SAB prefix (Siemens?) is a prefix not as widely known as, say, the Intel devices (P2111) so you did well to come across those.

The programmer I'll be using to program your PROMs with also has a handy IC testing feature which includes once-common static and dynamic RAM ICs, so if you'd like those tested feel free to include them with the PROMs. However, I see no reason to assume that any of them will be faulty.

Unfortunately I wouldn't be able to test those in the MK14 as they are one of the few ICs which are soldered rather than socketed in my particular machine - when I built it I happened not to have any IC sockets with the right number of pins, and I was impatient to get it built and up and running.

There must, somewhere, be large old redundant PCBs full of 2111 RAM ICs just lying around waiting to be found. I used to see a lot of that sort of thing in cardboard boxes at the larger radio rallies during the nineties.

Re: MK14 schematic revisions
 

They are coming from Germany, so I expect a week or two - I will send them with the PROMs if I may as there is no rush on the build and it will be good to be sure they work!

From looking around the internet, the RAM seems to have been commonly used in old Atari arcade games - unfortunately arcade boards generally fetch high prices these days, so not really a viable option! (I did scour the internet looking for cheap boards or spares from the arcade spares suppliers, but no luck)

And yes - I understand these are Siemens.

Re: MK14 schematic revisions
 

Sounds like a bargain. I wasnt able to find a datasheet for the SAB2111A but it would be surprised if its not compatible, 2111s were used in all kinds of products so it would be bzarre to make a device rhat wasnt 100% compatible, and the MK14 hardly stresses them timing wise.

Re: MK14 schematic revisions
 

Information on these is so scarce that I was worried they might not actually be RAMs at all, just some other IC which had 2111 in the part number.

However, I did find this one page referring to the use of SAB2111s as substitute 2111 RAMs for an old development system.

https://www.***********/photos/51699638@N06/26956276139

Re: MK14 schematic revisions
 

This is the only data I could find - the actual part number of the devices I ordered is SAB2111A-D4 which is listed as static RAM 256k x 4 @ 450ns.

Re: MK14 schematic revisions
 

I have a single step circuit that can switch single step on and off, I believe. It is currently on a piece of Vero board but I could reverse engineer it if any one is interested. I last used it in the 80's you see.

Re: MK14 schematic revisions
 

No need, Pepper, that circuit is in the manual which is available from various places on the 'net'. It goes with the 'Single Step' program in the 'System' section in the original manual. The improved 'New' version of the MK14 OS has the Single Step code built in.

One word of warning, if you use the new OS and you don't add the Single Step hardware, it is necessary to tie the Sense-A input low, otherwise you'll find you can't run programs.

Re: MK14 schematic revisions
 

My circuit is not the same as the one in the manual and is switched. I am an original OS and PCB guy too.

Re: MK14 schematic revisions
 

The one in the manual is actually switched as well, so you can swap between Single Step and normal running.

If you use your MK14 from time to time (rather than just maintaining it in running order as a museum piece) the 'New' OS is a big improvement over the old, requiring fewer keypresses to enter each byte of data and also incorporates the support routines for the tape interface (easily built on a bit of veroboard) and a handy jump offset calculator.

I'm surprised to hear that an issue V MK14 would have the 'old' OS, which is distinguished by the fact that it starts up with a '---- --' prompt, rather than the '0000 00' prompt of the 'new' OS.

Re: MK14 schematic revisions
 

It is all a learning exercise for me even all these years later, it would see. When I built the kit I never knew that I had anything other than the same version as everyone else, but as my kit starts up with 0000 00 and the board says V on it I must have the later version or the ROM. Hope it works with my replica Version I board...

Re: MK14 schematic revisions
 

It does, you just need to tie Sense-A low if you do not add the optional single step hardware. Otherwise I think you will be able to enter code OK, but you won't be able to run it.

Re: MK14 schematic revisions
 

Well after some head scratching I now know what you mean. The trouble is that the Mk14 I purchased is a Rev V board with a V2 OS, but I was supplied with a manual for V1 OS. That explains why I spent lots of time correcting the manual all those years ago...:-)

Re: MK14 schematic revisions
 

There is an excellent pdf copy of the late version MK14 manual on Martin Lukasek's website here

http://www.8bity.cz/files/MK14/mk14ManualV2_OCR.pdf

That is the version of the manual you need to work with if your MK14, whether early issue or late issue, has the 'new' OS, as it correctly describes the operation of the machine with the new OS.

Re: MK14 schematic revisions
 

Thanks for that, I've been looking for a manual for the v2 rom. Update: My replica mk14 isnt working, I'm not seeing any bus activity so its either a board wiring issue, bad crystal or bad sc/mp.... I've got a spare processor on the way so may be able to report soon!

Re: MK14 schematic revisions
 

Silly question, but is your original SC/MP an SC/MP II? The original SC/MP only operates up to 1MHz as far as I know. SC/MP II is up to 4MHz, although of course Clive chose to overclock it slightly, mainly because 4.43Mhz crystals were widely used in colour TVs and therefore cheap.

If you can tolerate the delay / risk involved in posting chips back and forth - an activity I know you are no stranger to - I'd be happy to test any suspect ICs in my MK14.

The crystal you can test independently by knocking up a simple logic IC based oscillator like this one, attached, found as a web image. Alternatively just fit any crystal you can find in the range from 1MHz to 4MHz in the MK14 - if your original crystal is at fault the machine will run with any other reasonable crystal frequency, just not at the normal speed.

Also definitely check the states of CPU pins which can halt the CPU, such as RESET and other less obvious ones.

The actual SC/MP datasheet seems quite hard to find, here it is presented in unconventional one-page-at-a-time html format, which is better than nothing.

http://searle.hostei.com/grant/SCMP/index.html

SC/MP applications handbook packed with all sorts of SC/MP information here on bitsavers:

http://bitsavers.trailing-edge.com/c...book-Feb77.pdf

Re: MK14 schematic revisions
 

Yes, its a SC/MP II, I just looked at it and its marked ISP-8A/600 which is a SC/MP 2 according to wikipedia. I'll hopefully be able to give it another look with the 'scope soon, and maybe breadboard an oscillator as you suggest.I've also got some 1 mhz & 4mhz oscillator modules which I should be able to rig up as an external clock to test if required.

Re: MK14 schematic revisions
 

Update!
Well, theres good news and bad news....
Good news is the the lack of bus activity I was seeing was because I missed out a track between the SC/MP and the crystal (oops!) and with this fixed all seems to be working well.... except the display is backwards! The keys also map to the wrong functions so I suspect I have something wrong around the 7445 chip.
This does tell me however that the TI 74LS157N multiplexers I bought from Farnell seem to work fine in this application, I am using them with 1977 7408j's to drive the display, so it did occur to me that possibly the older 7408s might have higher input capacitance which holds the signal long enough for the 74LS 157s to latch it. This is pure speculation as I have never seen any plausible explanation of why some 74LS157s might work when others dont.

It also shows my PROMS that so many people got programmed correctly for me are fine, which is another relief! The '8' key seems to working as the 'mem' key and I was able to stem through the first few bytes of the ROM and reading backwards the values are the same as the monitor listing.
It looks like when I have worked out what tracks need cutting and re-wiring I might need at some point get a new board made with all the corrections as I already have 5 "bodge" wires and am l,ooking at adding at least another 10...!

With a 9v power supply the regulator is getting quite hot, so I might have to look inti getting a bigger heatsink for it at the same time.

Slothie

Re: MK14 schematic revisions
 

Well done Slothie - I'm especially glad your PROMs turned out OK since they must literally been to more different countries now than I have in my lifetime.

At first glance it seems you might get away with just cutting and reversing the order of the column / cathode driver outputs from the 7445 to the display and keypad, but I haven't really thought it through so don't take my word for it. You could try it by fitting a socket with the appropriate number of pins onto a bit of veroboard and wiring that into a header plug or another socket with the output pins rearranged in reverse order, then plug that into the original socket for the 7445.

Considering this was just a 'thing you decided to do' completely from scratch, I have been impressed by your dogged determination to succeed, and it finally seems to be paying off.

If the mystery of the 74157s so intrigues you, once you have it working you can knock yourself out trying out all sorts of different brands of 74157 and post the results in a nice table here. ;)

Re: MK14 schematic revisions
 

I've been looking and discovered the version 5 schematic has pin numbers on the 7445, display and IC11 (80L95/74LS365) whereas on the v1 schematic which I was working from they were not marked, and in some cases the labelling is a bit vague.....
It looks like I have the column drives to the display reversed and also the row lines on the keyboard connecting to the wrong data lined via ic11..... if I'd worked from the v5 schematic originally i'd not have made these mistakes. I'm not sure if that accounts for all the symptoms but I like your idea of using a header and jumper wires while I experiment, I might make a veroboard that plugs into IC11 and I can move the connections around to see what makes sense. The display i'll just cut the column drive tracks an run wires between the display and the 7445 because I'm sure why that is wrong. I will definitely be redoing the board once its working and transferring over all the components to get rid of all my bodges!

I've finally persuaded my phone to upload a picture, the flash washed out the display but I'll get a better picture once I've got the display the right way round!

Re: MK14 schematic revisions
 

It looks great for something completely scratch designed!

I suggest that chopping / reversing the 7445 outputs before they diverge towards the display and keypad may fix BOTH of your problems at the same time.

Just for fun, a short program for you to enter and run when you get it working.

With the MK14, it's always a good idea to check through entered code at least once more before running, as just one wrong byte can send the CPU out of control and trash the rest of your carefully entered code in the process.

After entering all the bytes from 0F20-0F42 as below, hit Abort, O F 2 0, GO.

0F20-C4
0F21-0D
0F22-35
0F23-C4
0F24-00
0F25-31
0F26-C4
0F27-0F
0F28-36
0F29-C4
0F2A-3B
0F2B-32
0F2C-C4
0F2D-07
0F2E-01
0F2F-C2
0F30-80
0F31-C9
0F32-80
0F33-C4
0F34-FF
0F35-02
0F36-70
0F37-94
0F38-F5
0F39-90
0F3A-F1
0F3B-00
0F3C 79
0F3D 06
0F3E 74
0F3F-78
0F40-3F
0F41-38
0F42-6D