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Old 10th Apr 2022, 10:12 pm   #41
Mark1960
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Default Re: Yet another MK14 tape interface (ESP32).

Quote:
Originally Posted by Timbucus View Post
I actually bought a ready made expansion board from an ebay listing as well for one of my MK14's - I have not tested it on the JM Precision one but, see no reason it would not work.
Is that using a 32kx8 ram?

I made something similar on point to point wired proto board. I used an AS6C4008 but only 32k mapped into the low 2k of every 4k page. I modified it recently to an IS61C1024 128kx8 to test some devices cheap on aliexpress. The ram is battery backed using a max818.

Decoding is linked so that read from rom will also write to ram, so first excercise the monitor from prom with ram read disabled, then remove the proms and change the links to read from ram. The monitor will crash if its used to edit itself, I need to try and include some method of swapping pages.

Instead of using 2716 it might be easier to use 2816 or even sst39sf040. Just to avoid uv eprom erasing.
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Old 10th Apr 2022, 11:16 pm   #42
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Default Re: Yet another MK14 tape interface (ESP32).

I recall 28C16s being quite hard to get hold of recently - real ones, that is.

I have quite a few surplus 27E512 (EEPROMs) here, happy to let one or two go to a good cause but they are 28-pin wide bodied. I could supply one already programmed with the 'New' MK14 OS as a start-up. You would need to research how to programme them and maybe lash up an Arduino project to do it. (Or maybe you already have a USB programmer which can handle them)
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Old 11th Apr 2022, 7:07 pm   #43
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Default Re: Yet another MK14 tape interface (ESP32).

Sirius good point on the memory Hole I had forgotten that - but, it should be possible to make the mods to the JM Precision one as instruction are in the later manuals for the VDU.

Mark I don't have many details on the board as it was bought on a whim when my home made one refused to work (due to batch of faulty ram chips) - better photo attached - a nice feature is that it has the tape interface as well...

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Old 11th Apr 2022, 7:57 pm   #44
Mark1960
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Default Re: Yet another MK14 tape interface (ESP32).

Ok, so the ram is an 8kx8 and only a 74ls02 for decoding so I think it must just be filling holes in the 4k page. It might be removing some of the shadow areas, but you’d need a schematic to confirm.
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Old 12th Apr 2022, 9:11 pm   #45
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Default Re: Yet another MK14 tape interface (ESP32).

Thanks for all of the advice and information.
SiriusHardware, you are correct I would like to use a EPROM that I can program and add my fast loading routine. My original MK14 is an issue V, and the one I have ordered on EBay is the same issue, could not find issue VI currently on eBay.
I will try and contact Martin L to see if he has any of his adapter boards available.
Your suggestion of using a 4k Ram chip also makes a lot of sense and possibly a 4k Rom. I need to check to see if my fast load routine will fit into the existing Tape Interface Routines space, as mentioned previously I don't use the Store to Tape routine.
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Old 12th Apr 2022, 9:59 pm   #46
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Default Re: Yet another MK14 tape interface (ESP32).

It's good that the PCB you have coming is an issue V clone, because then the memory hole at 0200-07FF is already clear and you can map offboard memory into that space. I was thinking today about whether you could make the simplest of expansions using two fast (E)EPROMs and a large RAM, the second (E)EPROM programmed as a custom address decoder. Martin's expansion uses a GAL as the custom decoder but more people can program (E)EPROMs than can program GALs.

You might be able to find more code space by ripping out the jump offset calculator and single step routines as well, both are arguably redundant when you are developing the code off-machine.
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Old 13th Apr 2022, 5:46 pm   #47
coolsnaz2
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Default Re: Yet another MK14 tape interface (ESP32).

SiriusHardware
You are one step in front of me. My current fast load routine takes up 82 bytes. Store to tape, Load from tape and offset calculation (0052-009C) is 74 bytes. Not sure about Single Step routine, maybe you can confirm. I may have a previous version of the fast load routine that uses less memory, I will check.
If I wanted to use the existing Rom type, are they available, and are they easy to program. I have the original MK14 eprom programmer, but have never used it.
I would then leave the RAM expansion off board as you suggested, and have the standard RAM on-board. Thanks again for all your help.
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Old 13th Apr 2022, 9:47 pm   #48
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Default Re: Yet another MK14 tape interface (ESP32).

If you are considering having RAM in the onboard sockets you need to find some 2111 RAMs or alternatively AMD AM9111s, the AMD version of the same chip.

I have a small stash of blank MK14 compatible N82S131N PROMs and a programmer to program them with - I don't mind letting the occasional pair of those go at cost. Unfortunately your rather rather rare official MK14 PROM programmer is specifically intended to program the National Semiconductor DM74LS571, they come up from time to time but are usually quite expensive, about £12-£14 per chip was not unusual the last time I looked.

Don't be fooled into buying the TESLA version of the 74LS157, the MH74LS571 - they are compatible in read mode but they have a completely different programming regime so your programmer can't programme them. There are people on this forum who can program them but if you don't want to have to be dependent on other people for programming then that is not your ideal choice.

If you develop your code to the point where you consider it to be the fully working final version I can program a pair of PROMs with your patched code at that point, should you wish. You would need to be ultra sure the code was good because as I am sure you know the PROMs are one-shot, once programmed they can not be erased and programmed again.

While you are experimenting / developing your code you can always just patch a conventional EEPROM or EPROM or whatever you have the means to programme into the PROM sockets on the MK14, attached, a pic of my lashup for doing exactly that. I have both the old and new OSes programmed into the chip with the version link selectable so that I can check that my loaders work with both the old and the new OS. The chip itself is a Winbond 27E512, an EEPROM which can be erased and reprogrammed. The 'headers' which plug into the PROM sockets are just conventional IC sockets with wires soldered onto the contacts.
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Old 13th Apr 2022, 10:14 pm   #49
Mark1960
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Default Re: Yet another MK14 tape interface (ESP32).

Quote:
Originally Posted by coolsnaz2 View Post
SiriusHardware
You are one step in front of me. My current fast load routine takes up 82 bytes. Store to tape, Load from tape and offset calculation (0052-009C) is 74 bytes. Not sure about Single Step routine, maybe you can confirm. I may have a previous version of the fast load routine that uses less memory, I will check.
If I wanted to use the existing Rom type, are they available, and are they easy to program. I have the original MK14 eprom programmer, but have never used it.
I would then leave the RAM expansion off board as you suggested, and have the standard RAM on-board. Thanks again for all your help.
I think the single step code is only a couple of bytes to enable interupt and set halt flag prior to the xppc p3 that jumps to user code, probably not worth the problem of relocating all the routines that might be called from user code for display and keyboard interface.

Last edited by Mark1960; 13th Apr 2022 at 10:16 pm. Reason: Remembered it uses halt to trigger interupt.
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Old 14th Apr 2022, 10:07 pm   #50
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Default Re: Yet another MK14 tape interface (ESP32).

All
I think I am trying to run before I can walk.
I need to get a replica up and running before I look at updating the ROM, I already have 4 RAM chips I purchased to repair my original MK14. I may use SirusHardware lashup for the the ROM, this would allow me to confirm fast load routine before committing to N82S131N PROMs, SirusHardware may need your help at this stage, but maybe a few months away.
Over the next few days I will try and get fast (sync) loader down to less than 74 bytes.
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Old 15th Apr 2022, 7:26 pm   #51
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Default Re: Yet another MK14 tape interface (ESP32).

Quote:
Originally Posted by coolsnaz2 View Post
All
I think I am trying to run before I can walk.
I need to get a replica up and running before I look at updating the ROM, I already have 4 RAM chips I purchased to repair my original MK14. I may use SirusHardware lashup for the the ROM, this would allow me to confirm fast load routine before committing to N82S131N PROMs, SirusHardware may need your help at this stage, but maybe a few months away.
Over the next few days I will try and get fast (sync) loader down to less than 74 bytes.
I made a small PCB adapter to allow a 2716/2816 EPROM/EEPROM to be used to replace the 74S571's but ended up building but not needing it because I was able to get my Tesla PROMS programmed by sending them on a European tour. If you PM me you can send me a Self-adressed envelope and stamp and I can send you one if you like, I have 9 more than I need. It plugs into the left hand socket on turned pin headers with flying leads for the lower 4 data connections to the RHS PROM.

https://www.vintage-radio.net/forum/...3&d=1633785730
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Old 16th Apr 2022, 4:45 pm   #52
coolsnaz2
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Default Re: Yet another MK14 tape interface (ESP32).

Slothie
Thanks for the offer, I will PM you.
After starting with the MK14, I moved onto the Acorn Atom and BBC Computers. Both computers have long gone, but I do have the acorn memory board, 8k RAM and 8k ROM, see attached photo, and I have also been able to find manual on the web.
Most parts for my replica build have been ordered, just need to wait for them to arrive. I will keep you posted.
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Old 17th Apr 2022, 12:05 pm   #53
Slothie
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Default Re: Yet another MK14 tape interface (ESP32).

Thats fun, I have some PCBs to make an Acorn 1 that was the other computer I used at school for my nostalgia collection! I'm only building the processor/keyboard version, as that is what I had access to, and I have most of the components just they are in storage I don't have access to at the moment. The MK14 and Acorn 1 represent the beginning of computing I could get my fingers on, which is why I guess I am obsessed by them!
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Old 18th Apr 2022, 6:42 am   #54
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Default Re: Yet another MK14 tape interface (ESP32).

Quote:
Originally Posted by coolsnaz2 View Post
Slothie
Thanks for the offer, I will PM you.
After starting with the MK14, I moved onto the Acorn Atom and BBC Computers. Both computers have long gone, but I do have the acorn memory board, 8k RAM and 8k ROM, see attached photo, and I have also been able to find manual on the web.
Most parts for my replica build have been ordered, just need to wait for them to arrive. I will keep you posted.
If you need any photos of the Acorn Eurocards, feel free to ask me. I have a couple of the machines, with at least the following boards :

6502 CPU
6809 CPU
40 column teletext VDU
80 column VDU
The normal 8K ROM/RAM board
8271-based disk controller
Econet

I also have the keyboard which is in the same case as an Atom.

Oh yes, got some Atoms too, inlcuding the econet board for that machine. And I think one of my Atoms has an I/O Eurocard inside (the Atom expansion connector is the same pinout of course).
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Old 18th Apr 2022, 11:23 am   #55
Slothie
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Default Re: Yet another MK14 tape interface (ESP32).

Quote:
Originally Posted by TonyDuell View Post
If you need any photos of the Acorn Eurocards, feel free to ask me. I have a couple of the machines, with at least the following boards :

6502 CPU
6809 CPU
40 column teletext VDU
80 column VDU
The normal 8K ROM/RAM board
8271-based disk controller
Econet

I also have the keyboard which is in the same case as an Atom.

Oh yes, got some Atoms too, inlcuding the econet board for that machine. And I think one of my Atoms has an I/O Eurocard inside (the Atom expansion connector is the same pinout of course).
Thanks, I will, although it looks like it may be a while till I get access to my stuff!
I remember someone from Acorn came to out school to demo the Atom (I think it was before it was generally released, Acorn was trying hard to get into the education market), and I was blown away by the colour graphics. The best we had seen at that point was the psuedo-pixel graphics of the RML 38oZ and the atom's graphics were an order of magnitude better. We never got to "play" on it, though, and I didn't get my hands on an Acorn machine until the BBC Micro appeared.
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Old 22nd Apr 2022, 7:15 pm   #56
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Default Re: Yet another MK14 tape interface (ESP32).

For coolsnaz2, attached, the diagram for my 'lashup' EPROM-to-MK14-PROM adaptor as seen in post #48. Although it's a bit wasteful to use a 64K memory to emulate a pair of 512-byte PROMs I chose the 512 because they are abundant, available in both EPROM and EEPROM versions and both types / technologies have a relatively low VPP (programming voltage) which just about any 'modern' USB EPROM programmer in existence can handle.

As it happens, mine uses the power, address and low data nibble connections of the U2 PROM socket and only uses the high data nibble connections of the U3 PROM socket, whereas I think Slothie's ready-baked adaptor has the bulk of its connections to the U3 socket and only uses the low data nibble connections of the U2 PROM socket. It makes no difference.

Although A9 to A15 are stated to be tied low in the diagram you could make A15 switchable between 0V and a pullup to 5V so you can have two different code blocks programmed at 0000 and 8000 respectively, as I have, or make the A14 state selectable as well and choose from code blocks programmed at 0000, 4000, 8000, C000.
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Old 22nd Apr 2022, 7:50 pm   #57
Mark1960
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Default Re: Yet another MK14 tape interface (ESP32).

Or you could have 32 different 512 byte pages in the 27c512.

But don’t leave any unused address lines floating, connect to Vcc or Gnd.

Edit: Just realised Sirius has a note for that above the schematic.
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Old 22nd Apr 2022, 8:04 pm   #58
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Default Re: Yet another MK14 tape interface (ESP32).

I thought that showing the connections between the unused address pins and GND would make the diagram considerably less compact and tidy but it is true that the phrase 'connections omitted for clarity' is always something of a self-contradiction. I hoped the note would compensate for that.
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Old 7th May 2022, 10:17 pm   #59
coolsnaz2
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Default Re: Yet another MK14 tape interface (ESP32).

All, just an update on my MK14 replica build, see attached photos. I am still waiting for a keyboard overlay to arrive. Only had one problem relating to the keyboard edge connector not being the same as the original (Pin 2 is not connected to ground but is connected to reset switch).

I have decide to stay with the original ROM and RAM configuration for now. I may still develop my fast load routine to accommodate files greater than 256 bytes. The fast load procedure takes less than 30 seconds to load and subsequent loads take less than a one second.
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Old 7th May 2022, 11:43 pm   #60
Mark1960
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Default Re: Yet another MK14 tape interface (ESP32).

Not sure what type of keyswitches you are planning to use but there are a few suppliers on aliexpress that have similar switches to the ones fitted to my original mkIV. Looks like it could be an option for your replica.

These ones are lower profile, but the same supplier has the taller type similar to the P6 type.

https://www.aliexpress.com/item/4001009975677.html?mp=1

I haven’t placed an order yet, so not sure how good these are.
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