MK14 schematic revisions

[DeltaAlpha52]

Originally Posted by ChrisOddy

DeltaAlpha52 (Dave) contacted Trevor H to see if he still had any of his MK14 display PCBs avaliable, he doesn't but was kind enough to pass on the Gerbers so we could get some made. He was also happy for the files to be made avaliable here (attached).

I have had some boards made and have 3 spare which I can pass on to forum members, PM me with your address and I'll pop them in the in the post.

Chris

Thanks Chris - now I have a nice new display for the MK14.

I used a set of female connectors on the MK14 so I used pins on the display PCB making easy to change them when required.

Was thinking maybe the bigger displays might be even nicer. Trevor was not willing to part with those so I think maybe some Kicad work might be in order.

Cheers
David

[DeltaAlpha52]

Hi all

I've got a second MK14 PCB, version VI, that I would love to assemble, I've got a SC/MP chip and all the logic chips, and can provide suitable displays and buttons etc., but . . . . . . I've not got any memory or the proms

Can anyone suggest the best place to get the 2111's from ?

Is someone able to provide me with some proms ?

and finally the INS8154N chips - any thoughts?

Thanks for all your help in getting me a replica of my original MK14 up and working. The original was modded so much I suspect it was quite badly damaged - but I do so wish I had held onto the bits.

Stay safe
David

[Slothie]

Originally Posted by DeltaAlpha52

Hi all

I've got a second MK14 PCB, version VI, that I would love to assemble, I've got a SC/MP chip and all the logic chips, and can provide suitable displays and buttons etc., but . . . . . . I've not got any memory or the proms

Can anyone suggest the best place to get the 2111's from ?

Is someone able to provide me with some proms ?

and finally the INS8154N chips - any thoughts?

Thanks for all your help in getting me a replica of my original MK14 up and working. The original was modded so much I suspect it was quite badly damaged - but I do so wish I had held onto the bits.

Stay safe
David

The easiest to get 2111 compatible is the AMD AM9111, although be careful on eBay because some people seem to have the idea they are "rare" and "collectable" these days and want huge amounts for them. There seem to be a few chinese sellers with them, usual caveats apply.

As for the 8154... they are getting pretty rare. If you have a fat wallet then there are brokers like Littlediode that have them, they do pop up on eBay et al once in a while. I have dreams of designing a plug in replacement that are, unfortunately, still in the dream stage...

There are people on eBay who regularly advertise pre-programmed SCIOS ROMs, which is an option. There are also a couple of people on here who can program compatible PROMs if you have the correct type but I will let them volunteer themselves The different versions by different manufacturers are all compatible when in use, but have different programming requirements and procedures. As has been mentioned I am trying to build my own programmer but that project is not complete... My projects seem to get fast progress in short bursts followed by long periods of "meditation".

[Slothie]

If you get stuck with PROMs I did build a prom adapter that will allow a 2716 EPROM or 2816 EEPROM to be used in place of the 2 PROMS. The 2816 has the advantage that it is programmable with an Arduino. It plugs into the left hand PROM slot and has flying leads to got to the right hand proms data pins. I could stick one in the post to you.

If you use a turned pin IC socket and turned pin headers you won't damage the IC socket!

Ian

[SiriusHardware]

Dave, if you can source your own DM74S571, N82S131N or AM27S13 PROMs I will programme them for you, no charge but a self addressed and stamped jiffy bag is always appreciated. Be aware that buying blank PROMs can be a bit of a minefield, one Little supplier I tried to use recently sent me used (therefore useless) PROMs.

I can not currently programme the Tesla branded MH74S571. Others here can and may also have some spares they can sell to you.

I do have a small stock of 82S131, you can have a pair for what the chips cost me, but a pair of Teslas from elsewhere will most likely be cheaper.

[SiriusHardware]

The issue VI's most important unique feature, compared to all other original and replica MK14s, is that it has the address, data and control signals tracked to the contacts on the lower side of the edge connector.

You could therefore make a plug-in board containing an address decoder and a common RAM (6116?) and EPROM or EEPROM (2716 / 2816) and leave the onboard PROM and RAM sockets empty until such time as you can find something to put in those sockets.

[DeltaAlpha52]

Originally Posted by Slothie

If you get stuck with PROMs I did build a prom adapter that will allow a 2716 EPROM or 2816 EEPROM to be used in place of the 2 PROMS. The 2816 has the advantage that it is programmable with an Arduino. It plugs into the left hand PROM slot and has flying leads to got to the right hand proms data pins. I could stick one in the post to you.

If you use a turned pin IC socket and turned pin headers you won't damage the IC socket!

Ian

That sounds very useful - I've got a number of 2816 EEPROM, and a programmer, that I used for my Nascom 2 to replace the original ROMS that needed -5v.

Do you want a SAE ?

Stay safe
David

[Mark1960]

I can check on shipping costs from ABRA electronics, I think they only ship to Canada and US but I could forward a set of ram to you and I can probably also supply the 8154 at a reasonable cost. Send me a PM if interested.

I was thinking of building up a second VI to see how difficult it is to fit 2114 type ram. I’ll post pictures if I do it. Probably means a few track cuts and links.

[Slothie]

Originally Posted by DeltaAlpha52

That sounds very useful - I've got a number of 2816 EEPROM, and a programmer, that I used for my Nascom 2 to replace the original ROMS that needed -5v.

Do you want a SAE ?

Stay safe
David

I'll dig them out, if I can find them I think they will go letter post, they are really tiny and someone gave me some stamps! If not I'll PM you.

[DeltaAlpha52]

Originally Posted by Mark1960

I can check on shipping costs from ABRA electronics, I think they only ship to Canada and US but I could forward a set of ram to you and I can probably also supply the 8154 at a reasonable cost. Send me a PM if interested.

I was thinking of building up a second VI to see how difficult it is to fit 2114 type ram. I’ll post pictures if I do it. Probably means a few track cuts and links.

Thanks that sounds very interesting. Their price for 2111 chips is a lot better than elsewhere,

I'll PM you to discuss.

I've looked at the 2112 and 2114 chips - it's a pity they moved the gnd connection around, although it is more like where other chips have the gnd. It looks a bit like the 2111 was designed to be backward compatible with a 16 pin chip.

Martin did a daughter board that allowed the use of replacement chips for ram and rom but it uses GAL16V8 which I'm not sure about, and does sort of lose the original look of the mk14.

https://www.8bity.cz/2015/jednoduchy...-pro-soc-mk14/

Cheers

[Mark1960]

In addition to the two chip enables the 2111 also has separate output enable and write enable. The 2114 has a R/W and single chip enable, so we need to generate chip enable after R/W is set up. Slothie’s issue VI generates Read+Write with U17c, so we would need to qualify chip select with this and connect to pin 8. Also swap ground from pin 8 to 9. Write enable to pin 10 instead of 16.

Should be easy enough to replace two pairs of 2111 with one pair of 2114, but fitting the remaining 512 bytes in place of display/keyboard and 8154 is looking a bit more tricky.

[Slothie]

Originally Posted by Mark1960

In addition to the two chip enables the 2111 also has separate output enable and write enable. The 2114 has a R/W and single chip enable, so we need to generate chip enable after R/W is set up. Slothie’s issue VI generates Read+Write with U17c, so we would need to qualify chip select with this and connect to pin 8. Also swap ground from pin 8 to 9. Write enable to pin 10 instead of 16.

Should be easy enough to replace two pairs of 2111 with one pair of 2114, but fitting the remaining 512 bytes in place of display/keyboard and 8154 is looking a bit more tricky.

There is support for the 65X61 ram chips that have a chip enable and a R/~W signal, there is a link on the bottom, break the tiny track that is pre-connected on the "2111" side and connect the pads on the "65X61" side. Then the RAM enable goes low on read and write cycles, with the R/~W only going low on write cycles.

[SiriusHardware]

I've just read back through the entire thread - still an interesting read - in order to recall the part number of those alternative RAMs, the IM65X51s, only to return the end of the thread to find that Slothie had beaten me to it. I have a few spares of those which I acquired at very reasonable cost, PM me if interested.

The only drawback with those is that they are incompatible with the original SOC VDU due to a quirk in the way that version of the VDU drives the NRDS line, but Karen's Ortonview took that into account and so they should work with Ortonview.

The choice of 2111/9111 or 65X61 is determined via a solder blob link on the PCB underside, so is easily reversed as and when 2111s or 9111s become available.

[Mark1960]

For the 2114 in addition to qualifying chip enable with read or write, I also need to qualify it from the address lines. I think using U17C into a NAND gate is easier than using U16d.

This is more for the challenge of fitting 2114s into the MK14 than just replacing the 2111, though 65x61 might be a solution for David. I want to try and keep the keyboard and display at D00 and the 8154 at E00, also keep the low 2k free for the 6116 expansion.

[Timbucus]

I was a bit gutted I could not go along to the Computer Festival this weekend - spotted this photo that shows mk14man's collection of Machines...

https://twitter.com/HereBeDragons3/s...649091/photo/4

[SiriusHardware]

Took a bit of spotting (in photo four) as your link took me to the group of four photos. Hopefully that means that MK14man himself is still functioning as well. Is that an Acorn system 1 and a National Introkit (with optional keypad and display) that I see before me?

[Timbucus]

Yes indeed his site is back up after its outage as per a recent tweet https://twitter.com/mk14man/status/1445292287714631680

...well spotted on the Introkit Sirius I did notice but, I missed the Acorn System 1.

You all may also enjoy this Sinclair history with its detailed coverage of the MK14 written by non other than Tony Smith of the Scrumpi register article - I will try and make contact again to follow up on the Scrumpi research

https://blog.smittytone.net/2021/09/...w-it-all-began

[SiriusHardware]

Thanks for that further info, glad the site is back up and the second link is an interesting read. I wonder if any of the people who are in the fourth photo taking photos actually posted them online? Now there's a challenge for you, Tim.

[Timbucus]

Oh please give me a hard one... the thread has a closeup of the Introkit later as well.

https://twitter.com/Devilish_Design/...24112712609792

This is the fellow Triton owner and recent constructor of a SCRUMPI from Phil's PCB... I bet he has a real MK14 as well.

[SiriusHardware]

(Rueful Laugh....) I should have guessed that would be no obstacle for you.

Interested to see that one of the MK14s is a JMP, I'm surprised MK14m does not have a Czech 'Martin' replica and what.... no issue VI in the lineup? Hmph.