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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 17th Dec 2018, 6:12 pm   #1
retrotecchie
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Default Maplin Z80 CPU card

Hi all

Just found a 2011 thread about the old Maplin Z80A single board computer.

I have just been handed a box of 'stuff' from my old employers who were throwing out some old junk and in the box was one of these Maplin Z80 CPU boards.

Now, back in 1992 or so, I did some development work and built some control equipment based on these boards. I was hoping this was one of the original boards with the original Maplin M12 EPROM, but it turns out to be a 'modified' board with the custom EPROM I burned for that particular project!

Well, I can't find a copy of the original ROM anywhere. I have plenty of blank 2716s and there was also an EPROM programmer in amongst the junk, so I have the means to blow a new ROM. Has anyone out there still got one of these with the original M12 (not the later MS12) ROM to work with the hex keypad and 7 segment display.

I'd be happy with a copy of the EPROM (I can supply a blank 2716 or even copy a chip if you don't have a programmer) or can enter it by hand from a hex dump if anyone has one?

Thanks

Mike
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Old 17th Dec 2018, 6:50 pm   #2
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Default Re: Maplin Z80 CPU card

Is this the ROM?

http://mdfs.net/Software/Z80/Cards/Maplin.zip
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Old 17th Dec 2018, 6:54 pm   #3
SiriusHardware
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Default Re: Maplin Z80 CPU card

I'm sure I have the M12 code but it won't do you much good if you don't also have the companion display / keypad PCB (either the original version with proper switches or the later version with a membrane keypad).

If you have, or if you don't mind building one (I have the diagram for the keypad / display PCB) then I'll try to dig out the code.

Edit: Maybe MrBungle has beaten me to it?
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Old 17th Dec 2018, 7:40 pm   #4
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Default Re: Maplin Z80 CPU card

I just re-read that old 2011 thread and I see that at the time I could not find my M12 eprom, which didn't matter too much as it was the MS12 eprom (for the CPU PCB + Serial PCB) which people were after at that time.

I've just found my original M12 eprom now, so if the source MrBungle pointed you to doesn't contain what you want let me know and I will read it and post the code here. I see you obviously must have a keypad / display PCB to go with the CPU, I missed that on the first read.
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Old 17th Dec 2018, 11:10 pm   #5
retrotecchie
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Default Re: Maplin Z80 CPU card

Quote:
Originally Posted by MrBungle View Post
Is this the ROM?
No, that dump is the MS12 with serial IO, not the older version for the hex keypad/display.

I have both the original article from the Maplin magazine for the Keypad/display as well as an original unit in a box in the shed (somewhere), so all I am missing is the ROM.

The 2716 EPROM I have in this card has some fun code in it...the original application was a twin 35mm slide projector controller for a military project back in the early 90's, but that setup didn't use the keypad or display - just some funky I/O stuff.

A hexdump of the original M12 rom would be fantastic, SH.
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Old 18th Dec 2018, 2:29 pm   #6
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Default Re: Maplin Z80 CPU card

OK, I'll read the contents of the original EPROM this (Tuesday) evening and upload it here as a binary or Intel Hex file, or both.
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Old 18th Dec 2018, 9:39 pm   #7
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Default Re: Maplin Z80 CPU card

OK Mike, attached, a 2048-byte .bin (raw binary) image of the content of the M12 eprom for the Maplin GB86T Z80 CPU board when used with the matching display / keypad PCB.

I had to wrap it up in a .zip because the forum doesn't allow .bin files as attachments, but does allow .zip files. I couldn't find anything off hand to convert it into a line by line hex dump, but while I had the programmer set up I copied the code into a spare 2716 and tested it in my own Maplin Z80 CPU / Keypad and display combo, which I still have.

If you want the programmed 2716, it's yours, just PM me with details and I will send it down to you as fast as the Christmas post will allow.
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Old 18th Dec 2018, 10:09 pm   #8
retrotecchie
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Default Re: Maplin Z80 CPU card

Thanks....you are a star! Not too much code in there. I opened the bin file with a hex editor, took a snapshot of it and will punch it in to my ancient EP8000 programmer after work tomorrow.

Now I can go back 30 years and revisit a few old projects.

Thanks a million.


Mike
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Old 18th Dec 2018, 10:22 pm   #9
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Default Re: Maplin Z80 CPU card

More options if you can't wait: The attached .zip contains two files, one is the M12 eprom in Intel Hex form rather than binary form in case your programmer of choice does not support raw binary files, and the other is M12.txt which is a hex dump (with line start addresses) as the code would typically look when loaded into a hex editor.

Edit: Sorry, your post #8 was delayed by new user moderation. Hope it goes OK. Interesting that the code only occupies 0000-03FF, exactly half of the 2716. Does mean there's room for your own code in there, though. I have Intel Hex serial download routines in mine, supported by a connected 8251 UART.
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Last edited by SiriusHardware; 18th Dec 2018 at 10:45 pm.
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Old 19th Dec 2018, 3:17 pm   #10
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Default Re: Maplin Z80 CPU card

Another item which may prove interesting, a commented disassembly (to source) of the M12 Eprom.

Contains a few interesting snippets of information in the comments, such as information about the (non standard) allocation of bit-weights to display segments and several lookup tables within the code.
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Old 19th Dec 2018, 9:54 pm   #11
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Default Re: Maplin Z80 CPU card

Thanks for the extra info - very informative. I think I used the blank locations in a (copy of) my original ROM while I was originally developing code. My finished application for the board I have (with an EPROM containing the final code) didn't use the keypad or the display but instead read lookup tables from the top two ROM sockets which were fitted with ribbon headers and wired to a pair of D25 plugs. Into these plugs the user connected two EEPROM modules, external to the housing which contained information used to control a pair of 35mm Kodak slide projectors for use in a target shooting range.

User input was a set of switches (start, stop, pause, auto and manual plus a couple of others) allowing a sequence of slide numbers and timings to be automated as part of a multimedia training system.

I also used the board with the original keypad and a 2x16 LCD module in the companion 'programmer' for the system.

Happy days....the Territorial Army bought a dozen of these systems back in the early 90s. The unit I have was a factory 'spare' with the original production code.

Being the sad type I was back then, all my Z80 development was done on an ancient Spectrum +128 fitted with an internal cassette drive and a Centronics interface that allowed me to take hard copy of my code. I think I still have the +128 somewhere but the cassettes and all the hard-copy of my original development is long gone.

Thirty years, or so, on from the original project, I just think that revisiting my old Z80 stuff will happily keep me entertained when there isn't much on the telly.

Thanks for the help - I really do appreciate it.

Cheers

Mike
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Old 20th Dec 2018, 1:14 am   #12
SiriusHardware
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Default Re: Maplin Z80 CPU card

You're welcome. Mine still gets a run out every now and then.

If your CPU still has the original round NiCD memory backup battery on it, it might be worth desoldering that to inspect it or just pre-emptively replace it. There are a lot of retro systems starting to be heavily damaged by leakage from old on-board batteries now.
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Old 21st Dec 2018, 11:57 am   #13
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Default Re: Maplin Z80 CPU card

Further to the above: I've just checked mine and I'm glad I did. The battery has started to go bad, causing localised corrosion around it. The pad on the topside around the battery -ve terminal looked especially bad, as though it had been etched out of existence entirely - fortunately, after removal of the battery, there still proved to be metal underneath a heavy layer of whatever the top layer had turned into.

Several component leads in the near-area had turned luminous malachite green, as had the four or so CPU socket pins nearest to the battery. One through-hole connection had almost rotted away and has been salvaged by passing a snug fitting piece of tinned copper wire through the hole and soldering it to the cleaned up pads on both sides.

Strangest of all, the screen printing in the immediate area has lifted from the PCB surface and just drifts away like confetti when touched, a pity as the PCB was previously in perfect cosmetic condition.

Needless to say I have now permanently removed the battery. Its original function (to retain user programs in memory during power down) has been rendered partly redundant by the facility to download code into the system through a serial interface.

Oddly enough the battery does not look bad at first inspection, it was only when I popped off the white plastic lid that I found the battery itself covered in white crystalline snow.

If you have one of these in storage, I would urge you to check it now. Mine dates from the early 1990s.
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Old 21st Dec 2018, 4:44 pm   #14
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Default Re: Maplin Z80 CPU card

I spotted this thread (and the earlier one) and decided to register on the forum - so this is my debut post.

I have recently dug out my old Maplin Z80 Dev Board, which I appear to remember I did very little with. Perhaps now I will be able to tinker with it.

Thanks for the advice regarding the backup battery. Mine was starting to crytalize and would have soon eaten its way through the components, board and probably the shoebox the the board was in. I've removed it and soldered a battery clip to the board so I can have two AA rechargeable cells providing data retention for the RAM chip. This appears to be working OK.

My board has the stick-on keypad and an 8 digit 7 segment LED display and I have the original build manual and I've also found an earlier build article for the version with the proper key Hex pad.

Slowly working my way through the test information - it appears to be working OK so far.

Now to 3D print a case for the beast..

---
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Old 21st Dec 2018, 11:39 pm   #15
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Default Re: Maplin Z80 CPU card

My particular board doesn't have a battery or any of the charging/RAM backup components fitted. We didn't need any NVRAM for the original application so the production boards didn't have anything they didn't actually need. We didn't use the 8279 in the production version either, but for some reason this card did have one fitted. Perhaps it was a test unit - I forget as it was almost 30 years ago now.

One of the 'tricks' with business purchases through Maplin, back in the early 90s when (MPS was still part of the offering), was that you could speak to your 'rep' and order variations of standard kits if you bought them in any sort of quantity. We had a custom version of the kit with no battery or charging components, only two 24 pin DIL sockets (one for ROM and one 2K RAM) and no 8279.

Buying in twenty at a time, we made a significant saving without the unnecessary parts. I suspect the original shop-bought kit we bought in when I first played around with the Z80 is still hiding in a desk drawer at the old office somewhere. Either that or the battery rotted and it got thrown away

Mike
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Old 28th Dec 2018, 10:22 pm   #16
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Default Re: Maplin Z80 CPU card

Quote:
Originally Posted by Mirak005 View Post
Now to 3D print a case for the beast.
Can you upload a picture of your 3D printed case when you have done it? I for one, would like to see it.

Thank you.
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Old 2nd Jan 2019, 12:29 am   #17
SiriusHardware
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Default Re: Maplin Z80 CPU card

If the 3D printed case is still on the drawing board may I suggest either an open slot or a knock-out panel where the edge connector is so that Sinclair Spectrum peripherals like the Currah Microspeech, etc, can be plugged in (The layout of the double sided edge connector on the Maplin Z80 CPU is almost the same as that of the Sinclair Spectrum, presumably intentionally so).

Unfortunately no matter how you design it, it is unlikely that my Maplin Z80 CPU system, in its current form, will fit inside it. For well over half of its life now it has been attached to an MPF-IO PCB originally intended as an add-on for the 'Microprofessor' system - I bought this when Greenweld had some for sale many years ago. The address decoding on the MFP-IO board is such that none of the memory or I/O addresses on it clash with those on the Maplin system, so it was just a simple matter of wiring all the buses together.

The 8251 UART and Z80-CTC (as baud rate generator) are used in conjuction with additional code in the M12 EPROM to provide serial download of Intel Hex code through the RS232 connection at lower left on the MFP-IO PCB.
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Old 2nd Jan 2019, 10:38 am   #18
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Default Re: Maplin Z80 CPU card

Quote:
Originally Posted by SiriusHardware View Post
For well over half of its life now it has been attached to an MPF-IO PCB originally intended as an add-on for the 'Microprofessor' system - I bought this when Greenweld had some for sale many years ago. T.
Yes, they had a lot of parts for the MPF. I had (still have actually) the main MPF, the version with the VF display. I got many accessories for it when Greeneweld sold them off, though I can't remember if I got the IO board like you have.
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Old 2nd Jan 2019, 11:24 am   #19
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Default Re: Maplin Z80 CPU card

I would have liked a Microprofessor but never had one: A friend brought the LED version home from college to do a project, which was to write a functional 'digital clock' program for it (in assembly language assembled on an Amstrad CPC and then typed into the MPF by hand). We focused on getting the basic hours / minutes / seconds to increment and decrement and display correctly: He was going to add the time setting interface and 'increment time at one second intervals' bit later.

If I did come across one I would pair the MPF-IO board with that but in the meantime it provides what Maplin never really did supply as far as I know: A decent range of general purpose I/O for the Maplin system.
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Old 14th Feb 2019, 3:56 pm   #20
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Default Re: Maplin Z80 CPU card

Sorry Guys and Girls, Been out of action with the lurgy...

As requested a picture of my 3d printed case.

In three parts with a knock out section for a bus expansion connector.

Red button is connected to the cpu reset and the 4 holes are for port select LED's as per the original article.

There's also a hole in the back to take a USB B port so I can power the beast from an iPad power block. The current power leads are a little OTT.

Cheers,
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